Thomas M. Cooper Air Force Research Laboratory
Steven R. Flom Naval Research Laboratory
Michael Bockstaller Carnegie Mellon University
Cesar Lopes Swedish Defence Research Agency (FOI)
K1: Photonics I
Monday AM, November 28, 2011
Independence E (Sheraton)
9:00 AM - **K1.1
Degenerate and Nondegenerate Nonlinear Spectroscopy.
Eric Van Stryland 1 , David Hagan 1 , Scott Webster 1 , Dmitry Fishman 1 , Honghua Hu 1 , Trenton Ensley 1 , Markus Seidel 1 Show Abstract
1 CREOL, University of Central Florida, Orlando, Florida, United States
We will describe methods for rapidly characterizing the spectrum of nonlinear optical absorption as well as the dispersion of the nonlinear refraction in materials including semiconductors and organic dyes. A weak White-Light Continuum (WLC) can be used as the probe in pump-probe experiments and thus yield the spectrum of the nondegenerate nonlinear absorption. Kramers-Kronig integrals can then be used on the nondegenerate spectra to calculate the dispersion of the nonlinear refraction. Temporally delaying the probe gives information on the temporal dynamics of the nonlinear material. Alternatively, the WLC Z-scan relies on a spectrally intense femtosecond WLC which we have recently succeeded in making available over more than an octave bandwidth using ~150 fs pulses at 780 nm weakly focused into a ~1 m tube filled with krypton gas at ~2.5 atm. By seeding the WLC with a very weak (~0.02% of the pump beam) visible pulse we can increase the total energy in the continuum by >3x to obtain a few nJ/nm spectral energy density. Thus, WLC Z-scan experiments can simultaneously yield the nonlinear absorption spectrum and index dispersion for frequency degenerate nonlinearities. Such experiments have provided a wealth of data on the third-order nonlinear response of materials. Recently we demonstrated orders of magnitude enhancement in the two-photon absorption (2PA) coefficient of direct bandgap semiconductors when going to extremely nondegenerate photon pairs (i.e. energy ratios of ~10/1) which is in excellent agreement with a simple 2-parabolic band model. This has allowed gated detection of subgap radiation, including IR detection, using wide-gap semiconductors. Further applications, such as all-optical switching, should be possible. In addition, the inverse process of 2-photon gain should be identically enhanced, making the likelihood of a 2-photon semiconductor laser realistic. Analogous processes in organic materials are under study.Measurements of nonlinearities as a function of pulsewidth can further help determine the dynamics of the nonlinear response. Separating the bound electronic and nuclear contributions to the nonlinear refractive index, n2, is of interest to fully understand the nonlinear mechanisms in many materials but particularly for organic dyes. A detailed study of CS2 shows that measurements of n2 using pulses <50 fs are dominated by the bound-electronic response, while as the pulsewidth is increased nuclear contributions become dominant. A simple model of the kinetics shows the magnitude and temporal response of each nonlinear contribution to n2. Extending these models and measurements to organic dyes is underway.
9:30 AM - **K1.2
Chromophores for Nonlinear Absorption at TelecommunicationsWavelengths.
Chantal Andraud 1 Show Abstract
1 UMR CNRS-UCBL 5182, Ecole Normale Superieure de Lyon, Lyon Cedex France
We will present two different families of chromophores (heptamethine cyanines1 and aza-bodipy2) for two-photon absorption (TPA) based optical power limiting in the IR (particularly at telecommunications wavelengths). Spectroscopic properties of molecules will be discussed in this purpose3, 4.Optical power limiting will be presented on the basis of TPA and excited stateabsorption (ESA) properties.1 P.-A. Bouit, G. Wetzel, G. Berginc, B. Loiseaux, L. Toupet, P. Feneyrou, Y.Bretonnière, K. Kamada, O. Maury, C. Andraud Chem. Mat. 2007, 19, 5325-5335; P.-A. Bouit, R. Westlund, P. Feneyrou, O. Maury, M. Malkoch,E.Malmström, C. Andraud New J. Chem 2009, 33, 964-968.2 P.-A. Bouit, K. Kamada, P. Feneyrou, G. Berginc, L. Toupet, O. Maury,C.Andraud Adv. Mat. 2009, 21, 1151–1154.3 P.-A. Bouit, C. Aronica, L. Toupet, B. Le Guennic, C. Andraud, O. MauryJACS 2010, 132, 4328-4335.4 Q. Bellier, S. Pégaz, C. Aronica, B. Le Guennic, C. Andraud, O. Maury Org.Lett. 2011, 13, 22-25.
10:00 AM - K1.3
Principles and Applications of Small Molecule Assemblies for Organic Third-Order Nonlinear Integrated Optics.
Ivan Biaggio 1 Show Abstract
1 Physics, Lehigh University, Bethlehem, Pennsylvania, United States
For applications in third-order nonlinear integrated optics it is necessary to develop organic materials that combine a large third-order susceptibility, a high optical quality, and the ability to integrate them with existing guided wave technology. This work will discuss how this aim was achieved by developing optimized small molecules and their corresponding dense single-component supramolecular assemblies. While larger molecules can have larger third-order polarizabilities, they are generally more difficult to handle and to assemble into a dense solid state where their nonlinearity is not diluted. Small molecules, on the other hand, can be optimized (by donor-acceptor substitution around a compact conjugated system) to obtain a third-order polarizability that approaches the fundamental limit. This allows dense single-component assemblies of such molecules to have a third-order susceptibility three orders of magnitude larger than fused silica. The design principles that have enabled the developed of the individual molecules as well as of supramolecular assemblies that combine both a high third-order nonlinearity and a high optical quality will be discussed. The final result of these developments is an organic molecular material that can be assembled via molecular beam deposition from robust small-molecule constituents. In particular, the “DDMEBT” molecule combines a high third-order polarizability with a non-planar structure that leads to a very high degree of homogeneity and flatness in the vapor deposited thin films. These films are essentially amorphous, homogenous on the sub-micrometer scale, nanometer flat, and they can be deposited on a variety of substrates. One important demonstration has been their integration with the silicon photonics platform to build silicon-organic-hybrid devices where the organic molecular material could homogenously fill nano-scale gaps between silicon ridges, providing the off-resonant third-order nonlinearity for ultrafast all-optical switching.
10:15 AM - K1.4
Linear and Nonlinar Optical Properties of Vapor Deposited Organic Thin Films for All Optical Switching.
Michelle Fleischman 1 , Benjamin Breiten 2 , François Diederich 2 , Ivan Biaggio 1 Show Abstract
1 Physics, Lehigh University, Bethlehem, Pennsylvania, United States, 2 Laboratorium fur organische Chemie, ETH Zurich, Zurich Switzerland
We review the material properties of recently developed small-molecules assemblies for third-order nonlinear optics that can be vapor deposited in the form of thin films. We will first describe the molecular properties, in particular the linear and third-order polarizability, and then discuss how these molecular properties are reflected in the macroscopic material parameters of vapor deposited thin films.An important example is the the DDMEBT molecule (2-[4-(dimethylamino)phenyl]-3-([4-(dimethylamino)phenyl]ethynyl)buta-1,3-diene-1,1,4,4-tetracarbonitrile). DDMEBT has its longest wavelength absorption peak centered around 527 nm, and its third-order polarizability at 1.5 μm is real with a rotational average of 6±1 × 10E48 m5/V2, which is large both with respect to the size of the molecule and to the fundamental quantum limit. DDMEBT and related molecular designs can sublimate without decomposition at low temperatures between 100 and 200 degrees centigrade, and form high quality organic thin films upon molecular beam deposition on any substrate. The thin films are essentially amorphous, optically homogenous on the sub-wavelength scale, nanometer flat, and in general of high optical quality. We report on the linear and nonlinear optical properties of these thin films in various waveguide geometries, including refractive index, propagation losses, robustness, and shelf-life of years.
11:00 AM - K1.5
Energy Focusing Using J-Aggregate Heterostructures.
Gleb Akselrod 4 , Brian Walker 1 2 , William Tisdale 3 , Moungi Bawendi 1 , Vladimir Bulovic 3 Show Abstract
4 Physics, MIT, Cambridge, Massachusetts, United States, 1 Chemistry, MIT, Cambridge, Massachusetts, United States, 2 Physics, University of Cambridge, Cambridge United Kingdom, 3 Electrical Engineering and Computer Science, MIT, Cambridge, Massachusetts, United States
J-aggregates, which have coherently-coupled excited states and intense absorption cross sections, are also interesting due to the delocalized nature of their excitons. Although spectral control of excitons can be facilitated by energy transfer, the spatial control of excitons on length scales greater than Forter radius is an important challenge and could potentially enable photodetection and photonic signaling in biological environments.We report the focusing of J-aggregate excitation energy in both all-optical structures and optoelectronic devices. Large (20-fold) enhancement of acceptor fluorescence has been observed due to J-aggregates, which can also enhance the photocurrent in a hybrid organic/inorganic photodetector far more readily than a non-aggregated dye. We propose a model that characterizes device operation and exciton diffusion in these systems.
11:15 AM - **K1.6
Novel Two-Photon Absorbing Polymer-Nanoparticles Composites.
Paras Prasad 1 2 , Heong Sub Oh 1 , Min Ju Cho 1 , Won Jin Kim 1 , Guang He 1 Show Abstract
1 Institute for Lasers, Photonics and Biophotonics, State University of New York at Buffalo, Buffalo, New York, United States, 2 Chemistry, State University of New York at Buffalo, Buffalo, New York, United States
Highly two-photon absorbing polymer/semiconductor-nanoparticle composite materials are synthesized, which show a greater two-photon absorption (2PA) capability, a broader working wavelength range, and much better chemical/physical stability. The nonlinear transmission properties of both solution samples and solid film samples have been measured at ~800-nm wavelength in both fs- and ns-regimes. Their 2PA spectral property over broad spectral range has also been studied using femtosecond white-light continuum method, and the excited state dynamics have been investigated. Finally, their performances for optical limiting, stabilization and spatiotemporal reshaping of intense laser radiation field have been experimentally demonstrated.
11:45 AM - K1.7
Green Emitting Oligomeric Truxenes for Large Area Photonic Applications.
Colin Belton 1 , James Kirkpatrick 2 , Alexander Kanibolotsky 3 , Clara Orofino 3 , Peter Skabara 3 , Paul Stavrinou 1 , Donal D Bradley 1 Show Abstract
1 Centre for Plastic Electronics, Imperial College, London United Kingdom, 2 Mathematical Institute, University of Oxford, Oxford United Kingdom, 3 Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow United Kingdom
Star-shaped conjugated oligomers have recently attracted considerable attention as an alternative to conjugated polymers, in particular for photonic applications [1,2]. The excellent lasing performance, combined with the isotropic morphology and high photoluminescence quantum yield have been the principal reasons why this material class has been of interest . However, until now the emission of these materials has been confined to the blue part of the visible spectrum.We will present results from a new series of green emitting truxenes, incorporating the well known π-acceptor benzothiadiazole (BT). We have taken the opportunity to chemically tune the properties of the material by incorporating a single BT unit at different positions along each of the arms of a truxene molecule. We observe that the photo-physical properties of the molecule are governed primarily by the arm part of the structure and not the core. We use quantum chemical calculations, supported by suitable experimental data (PL, PLQY, Absorption and Raman) to show that the optical behaviour of the materials depends upon the degree of localisation of the hole wave-function. This is of particular importance when the BT unit is isolated on the end of the truxene arm and has important implications for the optical properties, including the gain.We will also present studies of the optical gain properties of the materials and go on to demonstrate their lasing performance. We will then speculate about the prospect of incorporating these materials in hybrid structures, where these green emitting materials are the active component of large area photonic devices, photo-pumped by blue InGaN micro-LEDs.  Tsiminis et al. Appl. Phys. Let. 94, 243304 (2009) Xia et al. Adv. Func. Mater. 19, 2844 (2009) Wang et al. Syn. Met. 160, 1397 (2010)
12:00 PM - **K1.8
Two-Photon Absorption Spectroscopy: From Nonlinear Absorbers to All-Optical Molecular Voltmeter.
Aleks Rebane 1 2 , Mikhail Drobizhev 1 Show Abstract
1 Physics, Montana State University, Bozeman, Montana, United States, 2 , National Institute of Chemical Physics and Biophysics, Tallinn Estonia
Simultaneous absorption of two photons, commonly known as two-photon absorption (2PA or TPA) is one of the most thoroughly-studied nonlinear-optical phenomena, and was also historically one the first NLO effect to be theoretically predicted and experimentally observed. Nevertheless, largely due to recent advances in femtosecond laser techniques, research interest in the 2PA and its practical applications continues to grow. We have developed a fluorescence-based measurement technique, which allows accurate absolute determination of the 2PA cross section values and their dependence on the excitation wavelength from visible to near-IR. In this paper we present some recent results where the quantitative 2PA spectroscopy is used to reveal fundamental properties of organic molecules as well as some emerging novel applications.One of the central questions is how to increase the 2PA cross section of particular functional organic chromophores. This in turn requires knowledge of quantitative relation between the 2PA properties and molecular parameters such as transition- and permanent electric dipole moments. We have performed a comprehensive study of a series of organic chromophores that are specifically designed to provide a systematic variation of intrinsic dipolar characteristics, which is achieved by chemically attaching particular electron accepting vs electron donating end group. We show that 2PA in the lowest dipole-allowed electronic transition is quantitatively described by the change of the permanent electric dipole moment in the same transition. This allows us to gain insight into the distribution of the molecular charges and also probe how the molecular charges interact with the electric field created by the surrounding solvent. It is now also conceivable to use the measurement of the 2PA as a way of determining the strength of the electric field acting at the location of the chromophore. We call this approach all-optical molecular voltmeter. We have performed experiments with fluorescent proteins, where we have determined the strength of local electric field inside beta barrel protein. We will discuss further applications of this technique to the measurement of nanometer-scale electric fields.
12:30 PM - K1.9
Optical Properties of Metal/Dielectric Multilayer for Wavelength Tunable Transparent Cathode in Top-Emitting Organic Light Emitting Diodes.
Bonhyeong Koo 1 , Kihyon Hong 1 , Sungjun Kim 1 , Kisoo Kim 1 , Illhwan Lee 1 , Juyoung Ham 1 , Jong-Lam Lee 1 Show Abstract
1 Advanced Materials Science, POSTECH, Pohang, Gyeongsangbuk-do, Korea (the Republic of)
OLED has shown potential in applications such as display and general solid-state lighting due to its steadily improved efficiency, superior color balance, and high brightness. Top-emitting organic light emitting diodes (TOLEDs) are more preferable for device integration due to the use of more complicated pixel circuits. Because the light is coupled out via the top cathode, formation of high transparency cathode is one of the most problematic processes. The most common transparent cathode materials are thermally evaporated metal or metal oxide films. Using Ag top electrode could induce the planar microcavity. However, due to the high work function of Ag, the device showed high operation voltage (>10V). Thus, the Ag is not appropriate material for transparent cathode.We investigated the optical properties of Top emitting Organic Light Emitting Diodes (TOLEDs) based on metal/dielectric wavelength tunable transparent top electrode. Different optical effects of metal such as aluminum or silver inter layer and outer dielectric layer such as tungsten oxide, silicon monoxide, gallium oxide, and magnesium oxide were identified in a joint experimental measurement and theoretical calculation. From these studies, we can optimize the suitable multilayer structure for wavelength tunable transparent top electrode in TOLEDs. We can choose diverse metal oxide which has different dielectric constant that influences surface plasmon effect between metal and metal oxide interface. Also, each dielectric material has different refractive index and extinction coefficient to achieve high optical transmittance over 80 % at characterized wavelength in terms of admittance diagram. Optimized metal/dielectric layers having high transmittance at the characterized wavelength can be employed as a transparent electrode for OLEDs with characterized emission. These led to the enhancement of light out-coupling and improvement of electroluminescent properties of TOLEDs.
12:45 PM - K1.10
Conicity and Depth Effects on the Optical Transmission of Lithium Niobate Photonic Crystals Patterned by Focused Ion Beam.
Ozgur Yavuzcetin 1 , Birol Ozturk 1 , Dong Xiao 1 , Sri Sridhar 1 Show Abstract
1 Physics, Northeastern University, Boston, Massachusetts, United States
We report on novel focused ion beam (FIB) fabrication techniques that can greatly improve the optical performance of photonic crystal (PC) structures in annealed proton exchange (APE) lithium niobate (LN) waveguides. The finite depth and conicity effects of holes in two dimensional LN photonic crystals have been theoretically analyzed through Finite Difference Time Domain (FDTD) and Finite Element (FE) methods. Our results indicate that conicity of holes causes refraction into the bulk sample, resulting in high transmission loss and no useful spectral features. We have used techniques such as gas assisted etching and developed pocketing for fabricating PC structures with better conicity. Although two dimensional PC structures (Bragg gratings or Fabry-Perot) have better conicity, light propagation is still effected by conicity as shown by our simulations and measurements. However, the electro-optic (EO) measurements indicate a significant amount of spectral shift showing the response of PC structure despite the conicity effects.
K2: Photonics II
Monday PM, November 28, 2011
Independence E (Sheraton)
2:30 PM - K2.1
Two-Photon Absorption, Photophysics, and Applications of a Zinc Porphyrin-Based Supermolecule.
San-Hui Chi 1 , Armand Rosenberg 2 , Animesh Nayak 3 4 , Timothy Duncan 3 , Michael Therien 4 , James Butler 5 , Steve Montgomery 6 , Guy Beadie 2 , Steve Flom 2 , James Shirk 2 Show Abstract
1 , NRL/NRC Fellow Residing at United State Naval Research Laboratory, Washington, District of Columbia, United States, 2 Optical Science Division, United States Naval Research Laboratory, Washington, District of Columbia, United States, 3 Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 4 Chemistry, Duke University, Durham, North Carolina, United States, 5 Physics, Pacific University, Forest Grove, Oregon, United States, 6 Physics, United States Naval Academy, Annapolis, Maryland, United States
The donor-π-acceptor-π-donor (D-π-A-π-D) structured bis(terpyridyl osmium)-(porphinato)zinc (OsPZnOs) in a DMSO solution was found to possess strong two-photon absorption (TPA) in the near IR. The peak of TPA is at 1100 nm and the corresponding cross section (δ) is 1300 GM, which is significantly larger than most monomeric zinc porphyrins. Such a D-π-A-π-D structure also leads to strong electronic coupling between terpyridyl osmium (donor) and zinc porphyrin (acceptor) groups and, as a result, gives greatly red-shifted and broad excited state absorption (ESA). Measurements of femtosecond time-resolved transient absorption showed that the ESA of OsPZnOs in DMSO is significant from 800 to 1200 nm with a peak near 1100 nm. The rise time of the transient excited state species is 700 fs and the lifetime is estimated to be several hundred nanoseconds. Since OsPZnOs possesses spectrally well-overlapped TPA and ESA bands and an ultrafast response it expected to be a strong nonlinear absorber useful for various photonic applications such as optical switching and noise suppression.The nonlinear absorption of OsPZnOs was investigated with nanosecond-pulsed power-dependent absorption measurements from 800-1100 nm. These measurements, performed in the free space geometry, showed strong nonlinear absorption in the near IR range of interest. Upon incorporation of an OsPZnOs solution in DMSO into microcapillary waveguides (inner diameter ~ 10 μm and path length ~ 2 cm), enhanced nonlinear absorption of OsPZnOs was observed because of the longer path length. In addition, for excitation near the TPA maximum at 1100 nm, an additional enhancement of up to 100× in the nonlinear absorption threshold was observed. The additional enhancement arises because higher local peak intensities in a waveguide enhance the efficiency of TPA pumping of the excited state. This reduces the turn-on threshold of nonlinear absorption.In summary, D-π-A-π-D structured OsPZnOs showed a strong fast ESA that overlaps a strong TPA in the Near-IR. These properties give it a promising nonlinear absorption that can be further enhanced through waveguide integration for nanosecond applications.
2:45 PM - **K2.2
Non-Linear Absorption in Organometallic Chromophores and Polymers.
Kirk Schanze 1 Show Abstract
1 Chemistry Department, University of Florida, Gainesville, Florida, United States
Platinum-containing pi-conjugated chromophores have been investigated in order to understand and optimize their non-linear absorption properties. The presentation will survey recent photophysical studies of polychromophores that contain multiple platinum-acetylide units linked together, as well studies carried out to characterize the properties of glassy polymers that contain a high concentration of chromophore units.ReferenceOrganoplatinum Chromophores for Application in High-Performance Nonlinear Absorption MaterialsChen Liao, Abigail H. Shelton, Kye-Young Kim, and Kirk S. Schanze, ACS Applied Materals & Interfaces 2011, Web ASAP, DOI: 10.1021/am200491y.
3:15 PM - K2.3
Photosensitive Epoxy-Based Polynorbornene Dielectric for MEMS and Microelectronics Packaging.
Mehrsa Raeiszadeh 1 , Paul Kohl 1 Show Abstract
1 Chemical and Biomolecular Engineering, Georgia Institute of Technolog, Atlanta, Georgia, United States
Photosensitive polymers are widely used in MEMS and microelectronics. Epoxy-based polymers are of special interest because of their excellent adhesion to substrates and modest cure temperatures. Among the most desirable attributes for photosensitive polymers is the ability to achieve high-aspect-ratio structures with excellent adhesion and high sensitivity. The acid-catalyzed activation of epoxy is an efficient way to achieve crosslinking and enhance the polymer properties, especially adhesion.Additives can be included in the polymer mixture to improve the sensitivity and photodefinability. An approach to creating higher sensitivity formulations with superior photodefinition properties without non-crosslinking additives has been found. Tetraphenylol ethane glycidyl ether (TPEGE), a tetra-functional epoxy based crosslinker, was used to enhance polymer properties.TPEGE was found to be sensitive to UV light with a high absorptivity in the range of 300 nm to 400 nm. The absorptivity of TPEGE was compared to 1-chloro-4-propoxy-9H-thioxanthen-9-one (CPTX) which is used as a photosensitizer in polymer mixtures at 365 nm. The absorptivities obtained for TPEGE and CPTX were 172,287 (L/mol.m) and 395,779 (L/mol.m), respectively. The absorptivity of TPEGE is almost half of the absorptivity of CPTX which is a significantly high value.The impact of TPEGE on the sensitivity, contrast, and aspect-ratio of Avatrel 8000P, an already photosensitive, negative-tone polymer, was evaluated. A small quantity, 3 wt% of solution, of TPEGE was added to Avatrel 8000P without any UV sensitizer. The new formulation yielded a contrast of 33.4, which is exceptionally high, compared to Avatrel 8000P (γ=7.4). This 4.5 fold improvement in contrast, was solely due to the 3 wt% addition of TPEGE. The D100 value obtained from the contrast curves was dropped from 66 mJ/cm2 to 14 mJ/cm2 by addition of TPEGE. Thus, TPEGE improved the sensitivity by a factor of 4.7.High-aspect ratio structures were fabricated with both formulations. The highest aspect-ratio obtained from Avatrel 8000P for hollow-core structures was 5:1, while the aspect-ratio was 13:1 in the new formulation. Addition of TPEGE improved the resolution, optical properties, and adhesion of the polymer and led to higher aspect-ratio features with straight side-walls and high fidelity. This example shows that using crosslinkers which have high UV sensitivity and participate in polymer crosslinking, leads to film properties which are superior to using additives which do not contribute to the polymer network.In conclusion, it has been shown that TPEGE has high UV-absorbtivity and can be used as an epoxy-based crosslinker to significantly improve the polymer’s photodefinability. Addition of TPEGE to the base polymer can result in high contrast, high sensitivity, excellent adhesion, and the ability to make high-aspect-ratio features, making the polymer suitable for MEMS and microelectronics applications.
4:00 PM - K2.4
Enhanced Extraction Efficiency of GaN-Based Light-Emitting Diodes Prepared by a Combination of Metal-Organic Chemical Vapor Deposition and Laser Interference Ablation.
Dajun Yuan 1 , Rui Guo 1 , Jeomoh Kim 2 , Mi-Hee Ji 2 , Suk Choi 2 , Jae-Hyun Ryou 2 , Russell Dean Dupuis 2 , Suman Das 1 Show Abstract
1 Woodruff School of Mechanical Engineering, Gerogia Institute of Technology, Atlanta, Georgia, United States, 2 2.Center for Compound Semiconductors and School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Gallium nitride (GaN)-based light-emitting diodes (LEDs) have been increasingly used for applications ranging from low power indicators to high power illumination due to their spectral and temporal control, longer lifetime, and robustness. However, to successfully replace conventional incandescent and fluorescent lamps, the efficiency of GaN-based LEDs has to be further improved. Here, we report on the development of a simple method for the fabrication of large area (> 3 cm2) two-dimensional periodic photonic crystal lattices on the LED surfaces that can increase the emission efficiency up to 300%. The base GaN LED wafers in this work are grown by metalorganic chemical vapor deposition using a reactor system equipped with a close-coupled showerhead growth chamber. The LED epitaxial structure consists of a 4 µm thick n-type GaN layer, an 11.8 nm thick In0.1Ga0.9N active region, and a 200 nm thick Mg-doped p-type GaN layer. Laser interference ablation of these wafers with a 10 ns pulsed Nd:YAG laser at 355 nm harmonic wavelength, and 10 Hz repetition rate creates periodic patterns. The laser irradiation causes the thermal decomposition of GaN into gaseous nitrogen and Ga droplets that remain on the surface and can be cleaned up by HCl. During laser interference ablation, the high-energy nanosecond laser selectively ablates the GaN surface. The resulting surface topography comprising a grid of flat mesas and V-shaped channels in the case of two-beam interference ablation, and hexagonal close-packed arrays of cavities in the case of three-beam interference ablation, follows the pattern of energy peaks and troughs in corresponding laser intensity distribution. Both the heights/depths and the sizes of mesas or cavities can be controlled by the input laser fluence. The flexibility of the laser interference ablation technique allows the pattern period to be varied in a relatively straightforward manner. Post-ablation characterization of the LEDs surfaces are conducted through atomic force microscopy and scanning electron microscopy. Photoluminescence results of patterned LED wafers made with different periods and laser fluences show an increase in emission efficiency of up to 300%. Thus, our novel method of rapidly producing well-defined photonic crystal patterns demonstrates high application potential for industrial fabrication of high-efficiency LEDs.
4:15 PM - K2.5
Toward Understanding Structural, Linear, and Nonlinear Optical Properties of Nanoscale Zinc and Cadmium Chalcogenide Magic-Size Quantum Dots: Insight from Computational Prediction.
Kiet Nguyen 1 2 , Paul Day 1 3 , Ruth Pachter 1 Show Abstract
1 , AFRL, Wpafb, Ohio, United States, 2 , UES, Dayton, Ohio, United States, 3 , GDIT, Dayton, Ohio, United States
Structures and energetics of small (AB)n (A = Cd, Zn; B = S, Se; up to n = 64) nanoclusters were studied using a combination of structure enumeration, Monte Carlo search, and local optimization. Binding energy calculations using density functional theory (DFT) were carried out to identify the so-called magic size quantum dots. Nanocluster growth and bonding patterns were examined and identified. Optical properties of nanoclusters as a function of size are examined using linear and nonlinear time-dependent DFT. The effects of ligands/solvent on the structure, stability, and spectra were also examined for selected clusters.
4:30 PM - **K2.6
Simulating Vibronic Effects in Two-Photon Absorption and Resonance Hyper-Raman Scattering.
Lasse Jensen 1 Show Abstract
1 Chemistry, The Pennsylvania State University, University Park, Pennsylvania, United States
Materials with strong two-photon absorption (TPA) are of interest for photodynamic therapy, optical data storage, two-photon fluorescence microscopy, and two-photon lithographic microfabrication. Vibronic effect due to electron-phonon coupling can be significant in large conjugated molecules that exhibit large TPA cross sections and needs to be included to correctly simulate the spectra. We have implemented an approach to calculate TPA vibronic profiles and resonance hyper-Raman spectra including both Franck-Condon and Herzberg-Teller terms based on the time-dependent theory of Heller. Here we will present our latest results focusing on the performance of this approach for describing vibronic effects in TPA and resonance hyper-Raman spectra.
5:00 PM - **K2.7
A TDDFT Investigation of One and Two Photon Absorption in Multibranched Chromophores.
Sergei Tretiak 1 Show Abstract
1 , Los Alamos Natl Lab, Los Alamos, New Mexico, United States
The nature of one- and two-photon absorption properties in several families of multibranched chromophores has been investigated using hybrid time-dependent density functional theory (TD-DFT) in parallel to experimental studies. We use recent extensions of TD-DFT to determine nonlinear optical responses and natural transition orbitals to analyze the underlying electronic processes. Our results are also interpreted in the framework of the Frenkel exciton model. In oligothiophene dendrimers the cooperative enhancement in absorption two-photon cross sections is explained by (i) an increase in the excited-state density for larger molecules and (ii) delocalization of the low-lying excited states over extended thiophene chains. Our joint experimental and theoretical studies demonstrate that combined spatial tuning of fluorescence and two-photon absorption (TPA) properties of multipolar chromophores can be achieved by introduction of slight electronic chemical dissymmetry. In agreement with experimental data, we found that introducing a triazole moiety into multibranched chromophores substantially modifies their optical behavior due to changes in electronic delocalization and charge-transfer properties between donating end groups and the branching center that can be controlled by the triazole ring.
5:30 PM - K2.8
Single Quantum Dot Spectroelectrochemistry Reveals the Role of Charging in Photoluminescence Blinking.
Christophe Galland 1 2 , Yagnaseni Ghosh 1 3 , Andrea Steinbrueck 1 3 , Milan Sykora 1 , Jennifer Hollingsworth 1 3 , Victor Klimov 1 2 , Han Htoon 1 2 3 Show Abstract
1 Chemistry, Los Alamos National Lab, Los Alamos, New Mexico, United States, 2 Center for Advanced Solar Photophysics, Los ALamos National Lab, Los Alamos, New Mexico, United States, 3 Center for Integrated Nanotechnologies, Los ALamos National Lab, Los Alamos, New Mexico, United States
Photoluminescence (PL) intermittency (blinking) is a universal property of molecular emitters. It has been observed for fluorescent molecules and artificial nanostructures such as nanocrystal quantum dots, carbon nanotubes, and nanowires. The occurrence of OFF periods in nanocrystal emission has been commonly attributed to the presence of an additional charge, which leads to PL quenching by non-radiative Auger recombination. However, the "charging" model was recently challenged in several reports. Here, to clarify the role of charging in PL intermittency, we perform time-resolved PL studies of individual nanocrystals while controlling electrochemically the degree of their charging . We find that two distinct mechanisms can lead to PL intermittency. We identify conventional blinking (A-type) due to charging/discharging of the nanocrystal core when lower PL intensities correlate with shorter PL lifetimes. Importantly, we observe a different blinking (B-type), when large changes in the PL intensity are not accompanied by significant changes in PL dynamics. We attribute this blinking behavior to charge fluctuations in the electron-accepting surface sites. When unoccupied, these sites intercept hot electrons before they relax into emitting core states. Both blinking mechanisms can be controlled electrochemically and under appropriate potential blinking can be completely suppressed. These results offer an explanation to recent controversial observations on PL intermittency and should assist in the development of nanocrystals with stable, blinking-free emission for applications from quantum information to high-sensitivity detection of chemical reagents and tracking of biological molecules.References:  C. Galland, et al., under consideration, Nature, (2011).
5:45 PM - K2.9
Two-Dimensional Colloidal Photonic Crystals for Visual Sensing Applications.
Jiantao Zhang 1 , Sanford Asher 1 Show Abstract
1 Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
We developed high diffraction efficiency two-dimensional (2-D) colloidal photonic crystals for molecular recognition and chemical sensing applications. We developed a convenient approach to prepare close packed 2-D colloidal crystal arrays (CCA) on mercury and water. Additions of co-solvents, such as alcohols to aqueous colloidal particle suspensions allowed the spreading and self-assembly of the particle arrays on top of mercury and water due to the lowered surface tension. We were able to fabricate large close-packed 2-D arrays with area of >70 cm2 within 30 sec on mercury and >280 cm2 within 2 min on water surface. We transferred the 2-D arrays onto various substrates. When the 2-D particle arrays were on reflective mirror surfaces, they diffracted >50% of the incident light. We then transferred the 2-D arrays onto functional three-dimensional (3-D) hydrogel films that show hydrogel volume changes in response to chemical stimuli. We altered the 2-D array spacing by controlling the swelling of the hydrogel films. We used these 2-D array hydrogel materials for chemical sensing applications. We tailored the hydrogels that embedded the 2-D arrays by introducing recognition groups. The binding of detected analyte molecules onto hydrogels resulted in the 2-D array spacing changes, which shifted the wavelength of the intense 2-D array diffraction. The diffracted wavelengths reported with high sensitivity on the analyte concentrations by changing color. We visually detected analytes, such as, pH, ions, etc. Reference:1.Zhang, J. T.; Wang, L. L.; Luo, J.; Tikhonov, A.; Kornienko, N.; Asher, S. A. J. Am. Chem. Soc. 2011, 133, 9152.
K3: Poster Session: High Performance Photonics
Monday PM, November 28, 2011
Exhibition Hall C (Hynes)
9:00 PM - K3.10
Light Splitting Function of Branched Chains of Microspheres Fabricated by Self-Assembly Process.
Tadashi Mitsui 1 , Yutaka Wakayama 2 , Tsunenobu Onodera 3 , Takeru Hayashi 3 , Naoki Ikeda 4 , Yoshimasa Sugimoto 4 , Tadashi Takamasu 1 , Hidetoshi Oikawa 3 Show Abstract
1 Surface Physics and Structure Unit, National Institute for Materials Science, Tsukuba Japan, 2 Nano-Electronics Materials Unit, National Institute for Materials Science, Tsukuba Japan, 3 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan, 4 Nanotechnology Innovation Station, National Institute for Materials Science, Tsukuba Japan
We fabricated ordered chains of transparent polystyrene microspheres that have 30°- and 60°-branched structures on a lithographically patterned Si substrate using a self-assembly process. The ordered chains act as coupled-resonator optical waveguides (CROWs), and we observed optical properties of propagation light through it. The spectra of propagation light within the chains were directly measured by guide-collection-mode near-field scanning optical microscopy (NSOM) techniques. Moreover, we observed detail structure of the CROWs by high-resolution scanning electron microscopy (HR-SEM), and performed a finite-difference time domain (FDTD) simulation to explain the NSOM spectra with including the results of HR-SEM observation. The HR-SEM images show that the neighboring microspheres are connected by a micro-joint which should be formed by swelling effect of polystyrene. We have found that the long-range light propagation of WGMs components is attributed to this micro-joint. The spectrum of light propagating to the 60°-branch shows some sharp peaks, which seem to be associated with whispering gallery modes (WGMs). On the other hand, the spectrum of light propagating to the 30°-branch shows rather broad peaks. The FDTD simulation suggests that the WGM component propagates to both of the 30°- and 60°-branches, and also suggests that almost all of the nanojet-induced mode (NIM) component propagates to the 30°-branch and little propagates to the 60°-branch. Therefore, the most plausible cause of the difference in the NSOM spectra is that the difference in propagation efficiency of the NIM component between the 30°- and 60°-branches. These results suggest that the microspheres’ branching chain itself has a splitting function, which is a kind of wavelength-selective filters. This microsphere branching chain can be applicable to fabricate smaller demultiplexers in integrated optical circuits than those of the photonic crystal waveguide since the microsphere chain has no cladding region. T. Mitsui, Y. Wakayama, T. Onodera, Y. Takaya and H. Oikawa, Nano Letters, Vol.8, (2008) pp.853-858. T. Mitsui, Y. Wakayama, T. Onodera, Y. Takaya and H. Oikawa, Optics Letters, Vol.33, (2008) pp.1189-1191. T. Mitsui, Y. Wakayama, T. Onodera, T. Hayashi, N. Ikeda, Y. Sugimoto, T. Takamasu and H. Oikawa, Advanced Materials, Vol.22, (2010) pp.3022–3026.
9:00 PM - K3.11
Strong Enhancement of 420~425nm Optical Wavelength of Blue LED by Using CaF2 Scintillating Crystals as a Cap.
Suzuka Nishimura 1 2 , Muneyuki Hirai 2 , Kazutaka Terashima 1 Show Abstract
1 , Shonan Institute of Technology, Fujisawa Japan, 2 , Solartes Lab, Fujisawa Japan
High power blue light emitting diodes have been attracting much attention for many uses around us. But, the output power does not always increase as the applied power increases, due to the piezoelectric effect of wurtzit structure.We worked on increasing the output power of blue LEDs by using scintillating crystals.It has been found that the strength of the light emitted by a blue LED was markedly enhanced by using crystal doped with Eu2O3 as a cap. The FWHM value of emitted light became 30% smaller due to the scintillating cap. The size of caps is around 5mm in diameter and 3mm in thickness.As an experiment we have measured the light emitted by a conventional LED with 3.0 V bias. This LED’s optical peak was 420nm, but emitted light was remarkably wide, from 350nm to 550nm. This includes a UV component. It means the LED structure contains GaN and In poor areas. Meanwhile the doped CaF2 crystals showed a scintillating effect. CaF2 crystals doped with Eu2O3 strongly absorb UV light of 330~420nm optical wavelength like a cutting filter. Also, crystals emit 420~425nm wavelength light. As a result, the UV light shifts to a light of around 420~425nm wavelength, and the LED light emission intensity markedly increases. In our experiments, the UV component was absorbed, while the light emitted around 420 nm strengthened by more than 30%. The FWHM value is improved by around 30%. It means the light emitted by GaN related devices can be enhanced by the use of Eu2O3 doped CaF2 crystals. These absorb shorter wavelength, resulting in a shift in wavelength to around 420~425nm. It can be seen that the blue light increases with a CaF2 disk. The shape of the window, Eu2O3 doping amount, and window thickness have not yet been optimized. Anyway, it should be noted that this window was able to enhance the power of the light in the 420~425 nm wavelength emitted by LED. At the meeting, we are going to describe the enhancement mechanism and the growth of the crystals.
9:00 PM - K3.12
Liquid π-Expanded Porphyrins as Optical Limiters
Daniel Gryko 1 2 , Agnieszka Nowak-Król 1 , Dominik Koszelewski 1 , Jan Lewtak 1 , Aleksander Rebane 3 , Mikhail Drobizhev 3 , Erich Beuerman 3 Show Abstract
1 Institute of Organic Chemistry, Polish Academy of Sciences, Warsaw Poland, 2 Faculty of Chemistry, Warsaw University of Technology, Warsaw Poland, 3 Department of Physics, Montana State University, Bozeman, Montana, United States
Optical limiting is a nonlinear effect consisting of a decrease in the transmittance of the NLO material under high-intensity illumination. Among different functions optical limiting devices can perform, the most useful one is the protection of optical elements, sensors and human eye against damage by exposure to a sudden high-intensity light. Dipolar or quadrupolar aromatic molecules have been shown to be of particular interest since they allow combining very fast (femtoseconds) intrinsic two-photon absorption (2PA) with somewhat slower reversed saturable absorption (RSA). We have developed the general principle to design porphyrins possessing low melting-point and we synthesized first liquid porphyrins: 5,10,15,20-tetrakis[3,4,5-tris(decyloxy)phenyl]porphyrin and 5,10,15,20-tetrakis[3,4,5-tris(undecyloxy)phenyl]porphyrin. We also developed new strategy towards π-expansion of porphyrin ring. Very recently we discovered the superior reagent for carrying out intramolecular oxidative coupling of porphyrins which avoids formation of troublesome side-products. All these developments combined with liquid porphyrin principle allowed us to produce first liquid porphyrin possessing reasonable two-photon absorption cross-section – suitable for optical limiting.
9:00 PM - K3.2
Microstructuring of Optical Quality Single Crystal Diamond by Two Photon Laser Induced Desorption.
Richard Mildren 1 , James Downes 1 , Josh Brown 1 , Benjamin Johnston 1 , Eduardo Granados 1 , David Spence 1 , Andrew Lehmann 1 , Leigh Weston 1 , Adam Bramble 1 Show Abstract
1 Department of Physics and Astronomy, MQ Photonics Research Centre, Macquarie University, New South Wales, Australia
There is currently intense interest in diamond micro- and nano-structured devices for use in applications as diverse as quantum information science, and nano-electromechanical systems, and diamond Raman lasers. Diamond’s hardness, mechanical anisotropy and chemical inertness present substantial challenges for engineering surface structures and currently a variety of methods have been investigated including combinations of plasma, ion implantation, chemical etching and laser ablation. To date, etching of the surface using laser induced desorption has received little attention and yet is a promising method for providing greater flexibility. Laser induced desorption (LID) is distinguished from laser ablation by a mechanism of mass removal that involves bond breaking and ejection of surface atoms or molecules via the decay of electronically or vibrationally excited quanta rather than via thermal or electrostatic forces (see eg. ). Material removal rates can be less than an atomic layer per pulse and achieved without substantial heating of the substrate. For diamond, LID has been observed only recently by using pulsed near band-gap laser irradiation [2,3]. Kononenko et al  showed that diamond was etched in air at rates 0.1-1x10-3 nm/pulse, orders of magnitude slower than rates typical of ablation (> 1 nm/pulse), when using sub-ablation threshold laser pulses of wavelength 248 nm. In our own studies into UV pumped diamond Raman lasers we have observed etching of pits approximately 50 nm deep by repeated exposure to 266 nm laser pulses of duration 30 ps, with etch rates as low as tens of carbon atoms per pulse . Here we show that graphite-free laser etching of microstructures in diamond is readily achieved with ultraviolet laser pulses of duration approximately 10 ns using a wide range of incident fluences below the threshold for ablation. For optical quality single crystal diamond, the etching rate is proportional to the fluence to the power 1.88±0.16 over the range 10-6 – 10-2 nm per pulse for incident pulse fluences 1 – 60 J/cm2. We show that the mechanism, which appears to have no threshold, is consistent with bond breaking and desorption of carbon species such as CO due most likely to the decay of two-photon excited excitons near the surface. The absence of a threshold heralds promise for creating a wide range of high resolution structures using direct write, near-field, masking and interferometric illumination techniques. A. Piqué, D. B. Chrisey in Direct-write technologies for rapid prototyping applications: Sensor, Electronics, and Integrated Power Devices, Academic Press, San Diego, USA, Ch. 14. (2002). V.V. Kononenko, M.S. Komlenok, S.M. Pimenov. V.I. Konov, Quantum Electron. 37, 1043, (2007).  E. Granados, D.J. Spence, R.P. Mildren, Optics Express, 19, 20422 (2011).
9:00 PM - K3.4
Development of Multicolor-Tunable Photoluminescent Ionic Liquid Crystals.
Kana Tanabe 1 , Yuko Suzui 2 , Miki Hasegawa 2 , Takashi Kato 1 Show Abstract
1 Department of Chemistry and Biotechnology, School of Engeneering, The University of Tokyo, Tokyo Japan, 2 Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin Univertisty, Kanagawa Japan
Ionic liquid crystals have attracted much attention because of their potentials to act as organized reaction media, anisotropic ion-conductive materials, and redox-active materials. In spite of their potential applications, there are only a few photoluminescent ionic liquid crystals reported. The limited number of luminescent ionic liquid crystals is partially due to the smallness of the π-conjugation of ionic liquid-crystalline molecules. Moreover, their small π-conjugation restricts the variety of the emission color. In this presentation, we will demonstrate syntheses, characterization, self-assembled properties and photoluminescent properties of a new series of color-tunable luminescent ionic liquid crystals. To achieve tuning of emission colors, intramolecular charge transfer character has been incorporated into tripodal molecules. These compounds have three chromophores in each molecule, incorporated with both electron donating moieties such as alkylaminobenzene and alkoxybenzene, and electron accepting moieties such as pyridinium, pyrimidinium, and quinolinium parts. These C3-symmetrical molecules self-assemble into liquid-crystalline columnar structures over wide temperature ranges through nanosegregation between ionic and non-ionic aliphatic parts. Photoluminescent emissions of these tripodal molecules are observed in the visible region both in the self-assembled condensed states and in solutions. For example, a pyrimidinium salt with didodecylaminobenzene moieties exhibits yellowish orange emission (λem = 586 nm in a thin film). Multicolor photoluminescent emissions are successfully achieved only by changing electron donating and electron accepting moieties of the compounds, covering the visible region from blue to red. For most of the compound, the fluorescent quantum yields are higher in the liquid-crystalline states than those in solutions probably due to the suppression of intramolecular rotation and/or vibration. It has been revealed that intramolecular charge transfer processes in the excited states and weak intermolecular interactions play important roles in the determination of the photoluminescent properties of the materials, by the measurements of UV–vis absorption and emission spectra, fluorescence lifetimes, and photoluminescent quantumn yields.  T. Kato, N. Mizoshita, K. Kishimoto, Angew. Chem. Int. Ed. 2006, 45, 38. K. Tanabe, T. Yasuda, T. Kato, Chem. Lett. 2008, 37, 1208.
9:00 PM - K3.5
Photonic Luminescent Structures of Porous Silicon.
Rocio Nava Lara 1 , Julia Taguena-Martinez 1 , Jesus Antonio del Rio 1 Show Abstract
1 , Universidad Nacional Autonoma de Mexico, Temixco, Morelos, Mexico
Porous silicon is a nanostructured material with a sponge like morphology that shows visible luminescence when the skeleton thickness is of a few nanometers, usually < 5 nm. At the same time, porous silicon multilayers are known by its photonic quality due to its large refractive index contrast between layers, but they does no show visible luminescence. Due to this fact, it is difficult to produce photonic luminescent multilayers of porous silicon to control its luminescence. In this work, it is shown that electrochemical etching of p+ substrates in an HF solution with polyoxometalate and H2O2 can be used to produce luminescent photonic multilayers that control the emission propagation and open the possibility for optoelectronic applications .
9:00 PM - K3.6
Effect of Silicon Nanowires on Photovoltaic Cell Performance.
Seung-Wook Baek 1 , In-Ji Lee 1 , Jae-Hyoung Shim 1 , Hyun-Ki Yoon 1 , Min-Ha Choi 1 , Gon-Sub Lee 2 , Jea-Gun Park 3 Show Abstract
1 Advanced Semiconductor Materials and Devices Development Center, Hanyang University, Seoul, 11, Korea (the Republic of), 2 National Program Center for Terabit-level Nonvolatile Memory Development, Hanyang University, Seoul, 11, Korea (the Republic of), 3 Department of Electronic Engineering, Hanyang University, Seoul, 11, Korea (the Republic of)
In recent years, silicon with various structural morphologies is widely used for solar cells and the minimization of reflection losses has received extensive interest for high efficiency solar cells. Alkaline etchants such as potassium hydroxide, sodium hydroxide, and sodium hypochlorite aqueous solutions are widely used for texturing mono-crystalline silicon surfaces. They result in the formation of surface pyramids due to the etching-rate differences between the <100> and <111>. In this paper, we present the single-crystalline Si nanowire on pyramid with extremely low reflectivity in depending on light incident angle to reduce the optical losses by wet chemical etching.The Cz Si had a resistivity of 1~3 Ω*cm, dimensions 1*1cm2 and a thickness of 200 μm. The wafers taken from an as-cut were subject to saw-damage removal, texturization applying standard alkaline etchant KOH/IPA, electroless metal deposition, and electroless selective etching with various etching time(0, 1, 2, 3, 4, 5, 7 and 10min). After the etching, wafers were diffused in a POCl3 furnace to obtain a doping layer with an emitter sheet resistance of 58 Ω/sq. Then, the Al paste (Ferro FX 53-112) and Ag paste (NS 33-501) were screen-printed on the back and front, respectively. After screen printing, the samples fired in a RTP system. The effective recombination lifetime were measured by using quasi-steady-state photoconductance (QSSPC). Then, an illuminated current–voltage characteristics and performance parameters of the solar cells were determined under one sun global solar spectrum of air mass (AM) 1.5 at 25 oC.The power conversion efficiency increased with electroless etching time up to 2 min from 10.87 to 11.73 %. Then, the power conversion efficiency rapidly decreased with electroless etching time from 11.73 to 7.6%. The trend of power conversion efficiency depending on electroless etching time was well correlated with that of the effective recombination lifetime depending on electroless etching time, i.e., the higher recombination lifetime led to the higher power conversion efficiency. In addition, The trend of power conversion efficiency depending on electroless etching time was well correlated with that of the surface reflectance depending on electroless etching time. Our study result demonstrated that Si nanowires improved the power conversion efficiency ~ 0.84% at a specific electroless etching time. Acknowledgement* This work was supported by New & Renewable Energy R&D program (2009-3030010090) under the Ministry of Knowledge Economy and the Brain Korea 21 Project in 2010.
9:00 PM - K3.7
Spectroscopic Ellipsometry Study of the Erbium Alloyed Aluminum Nitride Films.
Vishal Narang 1 , Dimitris Korakakis 2 Show Abstract
1 Department of Physics, West Virginia University, Morgantown, West Virginia, United States, 2 Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, West Virginia, United States
Rare earth alloyed semiconductors are always of interest to the scientific community due to their potential for providing thin film electroluminescent devices in visible and optical-telecommunication range [1, 2]. In case of erbium alloyed semiconductors, it has been shown that thermal quenching of electroluminescence decreases with increasing bandgap of semiconductors . This makes aluminum nitride (with a bandgap of 6.2 eV) a promising host for erbium doping. The atomic concentration of Er in AlN thin films and refractive indices of the films has been shown to influence the electroluminescence intensity . Also for piezoelectric applications, AlN films with 0.5 to 1.5% Er concentrations have shown the higher piezoelectric coefficients as compared to similar Er free AlN films .In this work, thin (250-800nm) AlN:Er films have been reactively sputtered using Er/Al alloyed targets. To understand the influence of Er on the optical and piezoelectric properties, optical response of the films is studied using the spectroscopic ellipsometry (SE) and SE data is used to determine the refractive indices of the thin films and atomic concentration of Er in the thin films. Atomic concentration of Er obtained from SE data is compared with the concentration obtained using X-ray photoelectron spectroscopy (XPS).. R.G. Wilson, R.N. Schwartz, C.R. Abernathy, S.J. Pearton, N. Newman, M. Rubin, T. Fu, J.M. Zavada, Appl. Phys. Lett. 65, (1994) 992.. K. Gurumurugan, H. Chen, G.R. Harp, W.M. Jadwisienczak, H.J. Lozykowski, Appl. Phys. Lett. 74, (1999) 3008.. P.N. Favennec, H. L’Haridon, D. Moutonnet, Y.L. Guillo, Electron. Lett 25, (1989) 718.. J.C. Oliveira, A. Cavaleiro, M.T. Vieira, L. Bigot, C. Garapon, J. Mugnier, B. Jacquier, Thin Solid Films 446, (2004) 264.. A. Kabulski, V. Pagan, D. Korakakis, Materials Research Society Symposium Proceedings, 1129 1129-V09-02 (2009).
9:00 PM - K3.8
Photonic Crystals on Erbium Doped Tellurite Thin Films for Broadband Enhanced Photoluminescence at near Infrared.
Pao Lin 1 , M. Vanhoutte 1 , J. Ho 1 , N. Patel 1 , V. Singh 1 , Y. Cai 1 , R. Camacho 1 , J. Michel 1 , L. Kimerling 1 , A. Agarwal 1 Show Abstract
1 Materials Processing Center, Microphotonics Center, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Two dimensional Er3+-TeO2 thin film photonics crystals (PhCs) are fabricated. These PhCs demonstrate broadband enhancement of PL emission at 1.55 um. The PhC structures are written by dual beam focused ion beam (FIB). Highly uniformed patterns with smooth surfaces are observed. A pattern resolution better than hundred nanometers is achieved. PhCs arrays with photonic lattice constants from 350 nm to 1700 nm are examined in order to optimize the PL extraction efficiency. Strong photoluminescence around 1530 nm is observed by 488-532 nm lasers pumping. A confocal microscopy with spectrometer is used to capture the broadband PL signals from individual PhC array. The emission enhancement factor and spectral dependent extraction ratio are analyzed to find the interaction between PL lightwave and PhC structures. By optimize the PhC structures, 1500 um-1560 um broadband PL is successfully converted between the PL emission layer and the external cavity. A 60 % enhancement of surface extraction efficiency is achieved when PhC with periodicity a=800 nm is applied. When photonic lattice constants a are smaller than the critical periodicity 600 nm, the PL light becomes confined inside the thin film layer. Simulation is also performed by two dimensional finite difference time domain (FDTD) calculation in order to explain the experimental observed anisotropic PL enhancements. The broadband PL enhancement enables Er3+-TeO2 PhCs thin film as a potential light source for three dimensional integrated photonic circuits.
9:00 PM - K3.9
Fabrication of Low-Loss Optical Waveguide Structures in Single-Crystal Sapphire Fibers for High-Temperature Sensing Applications.
William Spratt 1 , Mengbing Huang 1 , Chuanlei Jia 2 , Hua Xia 3 Show Abstract
1 College of Nanoscale Science and Engineering, Univeristy at Albany, Albany, New York, United States, 2 College of Physics Science and Technology, Shandong University, Dongying, Shandong, China, 3 RF and Photonics Laboratory, General Electric Global Research Center, Niskayuna, New York, United States
Single-crystal sapphire fibers possess superb chemical and thermal stability, making them an ideal candidate for optical sensing in extreme environments involving high temperatures (>1000 °C) and high corrosion. However, their sensing performance is hindered by a lack of effective methods to form waveguiding/cladding structures in sapphire fibers, which not only contributes to considerable optical loss, but also makes sensing difficult due to the highly multimode nature inherent in large diameter sapphire fibers. The core of this work focuses on the creation of internal cladding structures in sapphire fibers with excellent thermal stability up to 1700 °C and with a reduced number of optical wave guiding modes, through the use of ion beam modification. Single crystal fibers were uniformly implanted with MeV hydrogen ions to doses 1017cm-2, and subsequent thermal annealing at temperatures up to 1700 °C was performed in ambient. The resultant fiber structure consists of two regions: one within ~ 20 μm from the fiber surface serving as the cladding with a reduced refractive index due to ion beam processing, and the other as a core region below the cladding. The fiber exhibits strong waveguide effects even following annealing at 1700 °C, for example, about 80% of the incident light being confined within the fiber core with an optical loss of less than 0.3 dB/cm in the near-infrared spectral range. To gain insight into the physical processes affected by the implantation and annealing, planar sapphire wafers were processed in the similar way as the sapphire fiber. This allows for the determination of material properties and their evolution with processing conditions using a variety of analytic techniques such as Rutherford backscattering/ion channeling, nuclear reaction analysis, spectroscopic ellipsometry, and prism-coupling measurements. Furthermore, fabrication of multiple optical barriers within sapphire fibers is also demonstrated to create a novel fiber structure in which only a few optical modes are guiding through. Our work suggests that ion beam methods can be very effective for fabrication of waveguiding structures and potentially fiber grating structures within single-crystal sapphire fibers, to enable their applications in harsh-condition sensing.
Thomas M. Cooper Air Force Research Laboratory
Steven R. Flom Naval Research Laboratory
Michael Bockstaller Carnegie Mellon University
Cesar Lopes Swedish Defence Research Agency (FOI)
K4: Photonics III
Tuesday AM, November 29, 2011
Independence E (Sheraton)
9:30 AM - **K4.1
Development of Materials for Third-Order Nonlinear Optics.
Seth Marder 1 , Stephen Barlow 1 , Jean-Luc Bredas 1 , San-Hui Chi 1 , David Hagan 2 , Joel Hales 1 , Yesudas Kada 1 , Hsin-Chieh Li 1 , Jon Matichak 1 , Shino Ohira 1 , Lazaro Padilha 2 , Joseph Perry 1 , Eric Van Stryland 2 , Scott Webster 2 Show Abstract
1 Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 College of Optics and Photonics and Department of Physics, University of Central Florida, Orlando, Florida, United States
In this presentation we will discuss recent advances in the design, synthesis, characterization and application of molecules with large real and imaginary third-order optical nonlinearities, focusing on how variation in chemical structure relates to the observed nonlinearities.
10:00 AM - K4.2
Effects of High Concentration on Photophysical Properties of a Series of Nonlinear Dyes.
Joy Haley 1 , Jonathan Flikkema 1 2 , Matthew Dalton 1 3 , Douglas Krein 1 3 , Weijie Su 1 3 , Jonathan Slagle 1 4 , Daniel McLean 1 4 , Loon-Seng Tan 1 , Thomas Cooper 1 Show Abstract
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, Ohio, United States, 2 , SOCHE Student Research Program, Dayton, Ohio, United States, 3 , General Dynamics Information Technology, Dayton, Ohio, United States, 4 , Science Applications International Corporation, Dayton, Ohio, United States
The effects of high concentration on the photophysical properties of a nonlinear material have been of interest for some time in our group. It is well known in the literature that for a nonlinear absorbing dye to be the most effective, high concentrations are needed. The problem is that most photophysical studies in solution are done at low concentration. These low concentration studies are important for understanding inherent materials properties but it is also important to understand what happens in a material at high concentration. In addition to this, efforts have been made to study the effects of incorporating a dye into a solid matrix environment to better understand the constraints this environment has to a given material. To effectively make these measurements many of our traditional experiments were modified to accept either a thin cuvette of high concentration or a solid sample with a different geometry. Preliminary results reveal the formation of excimers (excited state dimers) with an increase in concentration. Excimers may form from either the singlet excited state or the triplet excited state depending on the molecule and provide a competitive pathway for deactivation of the excited state back to the ground state. Determining the rate of formation of the excimers has been done for several of our dye systems including an all organic two photon dye and a platinum containing organic dye. These results will be presented along with possible strategies for minimizing excimer formation in the future.
10:15 AM - K4.3
Nonlinear Light Propagation in Photopolymers: From Self-Trapped Beams to 3-D Optical Lattices.
Kalaichelvi Saravanamuttu 1 Show Abstract
1 Chemistry and Chemical Biology, McMaster University, Hamilton, Ontario, Canada
While liquid crystals, surfactants and colloidal crystal systems assemble into ordered phases to attain free energy minima, strikingly complex patterns can also emerge when condensed matter systems are perturbed away from equilibria. This talk will be an overview of research in our group into the dynamics of light beams that propagate while simultaneously initiating free-radical polymerisation in photopolymers. The consequent nonlinear and reciprocal interactions between the optical field and self-induced refractive index changes in the medium elicit a rich assortment of three-dimensional spatial patterns. These include self-trapping bright and dark beams, beam filamentation due to modulation instability, diffraction rings due to self-phase modulation and the formation of 2-D and 3-D bright and dark optical lattices. The potential of these optical phenomena to spontaneously inscribe complex 3-D polymer architectures that are inaccessible through conventional lithographic techniques and that would have advanced optical applications such as nonlinear photonic crystals will also be described.
11:00 AM - **K4.4
Design of Efficient Monolithic Hybrid Materials for Optical Protection.
Stephane Parola 1 , Denis Chateau 1 , Frederic Chaput 1 , Mikael Lindgren 2 1 , Cesar Lopes 3 Show Abstract
1 Chemistry Laboratory UMR ENS-UCBL-CNRS 5182 , University of Lyon - ENS Lyon, Lyon France, 2 Dept. of Physics, Norwegian University of science and Technology, Trondheim Norway, 3 , Swedish Defence Research Agency, Linköping Sweden
Nonlinear optical materials for optical attenuation and other applications have been studied for more than 2 decades. The studies have been, in most cases, performed on solutions. There has been a demand for high performance solid-state materials for different applications.1,2 In this perspective, the synthesis of monolithic siloxane-based hybrid materials highly doped by various platinum (II) acetylides derivatives was achieved with a new protocol based on a quick gelation reaction.3 Measurements of luminescence and optical power limiting for these hybrid materials showed efficient behaviour in the visible wavelengths for concentrations of chromophores as high as 400mM.In this communication, we will present the impact of the structure and the chemical composition of the matrix, spectroscopic properties, as well as the oxygen influence on the linear and nonlinear optical properties. Furthermore, the possibility of using the plasmon effect of metal nanoparticles to magnify the optical nonlinear properties of the chromophores will be discussed.1 R. Zieba, C. Desroches, F. Chaput, M. Carlsson, B. Eliasson, C. Lopes, M. Lindgren, S. Parola, Adv. Funct. Mater., 2009, 19, 235-241.2 R. Westlund, E. Malmstrom, C. Lopes, J. Ohgren, T. Rodgers, Y. Saito, S. Kawata, E. Glimsdal, M. Lindgren, Adv. Funct. Mater. 2008, 18, 1939-1948.3 D. Chateau, F. Chaput, C. Lopes, S. Parola, 2010, EP 10305377.3-2111 (2010).
11:30 AM - **K4.5
QM/MM Modeling of Two-Photon Absorption of Chromophores in Solvent and Solid Environments.
Hans Agren 1 , Arul Murugan 1 , Zilvinas Rinkevicius 1 Show Abstract
1 , Royal Institute of Technology, Stockholm Sweden
In recent time, we have devoted efforts on the quantum mechanics - molecular dynamics response approach, originally introduced by Mikkelsen, Kongsted and coworkers  and developed it for calculations of non-linear optical properties, like hyperpolarizability and two-photon absorption [2,3,4,5]. In this methodology, the full QM and MM interactions are accounted for in the evaluation of a given property. Underlying structures and trajectories are obtained by molecular dynamics or Car-Parinello-MM methods. In the talk I also highlight recent results on solvatochromatic effects and discuss some first results for solid or protein environments , and a discussion on the proper MM parametrization of such environments . A few highlights from our hybrid QM/MM based calculations are: (i) The well-celebrated structure-property relationship associated with the bond-length alternation and hyperpolarizability has been shown to break down in more polar solvents [2,3,4]; (ii) Two photon absorption cross sections for molecules in solvents have been computed free from any empirical parameters for the first time allowing for a quantitative comparison with experimental results; (iii) The optical probes have shown to exhibit significant structural variation depending upon the dielectric nature of the environment which in turn is responsible for their solvatochromic and enzymechromic shift in solvent and protein environments.  C.B. Nielsen, O. Christiansen, K.V. Mikkelsen, J. Kongsted, J. Chem. Phys., 126, 154112 (2007).  N.A. Murugan, J. Kongsted, Z. Rinkevicius, and H. Agren, Proc. Acad. Nat. Science (USA), 107, 16453 (2010). N. A. Murugan, J. Kongsted, Z. Rinkevicius, K. Aidas, and H. Agren J. Phys. Chem. B, 114, 13349(2010) N.A. Murugan, J. Kongsted, Z. Rinkevicius, and H. Agren, Phys. Chem. Chem. Phys. 13, 1290 (2011). N.A. Murugan, J. Kongsted, Z. Rinkevicius, K. Aidas, K. Mikkelsen, and H. Agren, Phys. Chem. Chem. Phys. 00, 000 (2011). (DOI: 10.1039/c1cp20611g) N.A. Murugan, J. Kongsted, Z. Rinkevicius and H. Agren, (Submitted to JACS) O. Vahtras, Z. Rinkevicius, N.A. Murugan, and H. Agren, (Manuscript under preparation).
12:00 PM - **K4.6
Ab Initio Study of Cyanine Dyes with Large Optical Nonlinearities.
Thomas Koerzdoerfer 1 , Sukrit Mukhopadhyaya 1 , Jean-Luc Bredas 1 Show Abstract
1 Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, United States
All-optical switching applications require materials with large third-order nonlinearities and low nonlinear optical losses. Recently, it was shown that a class of organic cyanine dyes exhibit favorable non-linear optical properties in solution, thus making these systems promising candidates for organic-based all-optical switches. Along with synthesis and experiment, ab-initio calculations can help to identify suitable materials, to gain a deeper understanding of the ongoing processes, and to study the influences of aggregation on the linear and nonlinear optical properties. However, due to the large size of the involved chromophores and the need to take electron correlation effects properly into account, a sufficiently accurate analysis of the nonlinear response of cyanines is a challenging task for modern computational chemistry. In this talk, I will discuss our recent results for several promising cyanines using a combined approach of density-functional theory and configuration interaction methods. In particular, I will discuss the influence of solvents and counterions as well as the impact of aggregation on the ground- and excited-state electronic properties of cyanine molecules.
12:30 PM - K4.7
Nanoimprinted Hybrid Silica Coatings: A Versatile Tool for Light Manipulation.
Alban Letailleur 1 2 3 , Cedric Boissiere 2 , Francois Ribot 2 , Clement Sanchez 2 , Jeremie Teisseire 1 , Etienne Barthel 1 , Elin Sondergard 1 , Christophe Couteau 3 , Gilles Lerondel 3 , Nicolas Chemin 4 Show Abstract
1 Surface du Verre et Interfaces, Saint-Gobain Recherche, Aubervilliers Cedex France, 2 Laboratoire de Chimie de La Matière Condensée de Paris, Collège de France - Université Pierre et Marie Curie, Paris France, 3 ICD - Laboratoire de Nanotechnologies et d'Instrumentation Optique, Université de Technologie de Troyes, Troyes France, 4 Composites and Coatings, Saint-Gobain Recherche, Aubervilliers France
In light emitting devices, a large amount of the light produced by the active layer is trapped inside the device because of internal reflection. Patterning the different interfaces induces an index gradient and light scattering and can therefore lead to an increase of the light output. Among the existing methods, Nanoimprint Lithography (NIL) emerges as a simple route for surface patterning at the sub-micrometer scale over large areas. To avoid multiple step processing and the poor stability of polymers resins, imprint of functional materials is required.Hybrid sol-gel materials form an innovative class of resists for NIL. They are based on the solution processing of organic precursors to obtain metal oxide. For instance we previously demonstrated the replication of patterns with sub-100 nm lateral size and aspect ratio greater than 1 into hybrids sol-gel silica (1). A combination of low viscosity and high reactivity enables fast and conformal imprint over several tens of cm2. (2) Furthermore, we demonstrate how the elaboration chemistry of the materials can be modified to adjust the process.(3) Due to their low dielectric constant, nanopatterned silica coatings are very suitable for direct applications in photonics, and integration in displays.Finally, tanks to the versatility of the sol-gel processing, other functionalities have been added to obtain multifunctional coatings. For instance, it was possible to graft NLO chromophores such as 2,4-dinitrophenylamine into the silica network and to successfully imprint the resulting layer. In the context of displays and lighting, we developed the introduction of colloidal quantum dots inside the patterned silica layer.(4) This last system is suitable for light conversion and extraction. As it absorbs around 400 nm and emits light in the visible range, such a layer can act as a conversion layer in LED devices. Moreover, the light output in the patterned area increased 60 % compared to the flat surfaces.References: 1) Peroz, C.; Chauveau, V.; Barthel, E.; Sondergard, E. Advanced materials 2009, 21, 5552) Letailleur, A.; Teisseire, J.; Chemin, N.; Barthel, E.; Sondergard, E. Chem. Mater. 2010, 22, 31433) A. A. Letailleur, F. Ribot,, C. Boissière, C. Sanchez, J. Teisseire , E. Barthel, N. Chemin, J Am Chem Soc, submitted.4) A. A. Letailleur, Th. Richardot, C. Boissière, C. Sanchez, C. Couteau, G. Lérondel, E. Barthel, E. Søndergård, N. Chemin, and François Ribot, Advanced materials, submitted.
12:45 PM - K4.8
Hybrid Silicon Nitride and Colloidal Nanocrystal Waveguides and Microdisks: A Highly Versatile Test Bed for Visible to near-Infrared Active Integrated Photonics.
Bram De Geyter 1 2 3 , Katarzyna Komorowska 1 3 , Zeger Hens 2 3 , Dries Van Thourhout 1 3 Show Abstract
1 Photonics Research Group, INTEC, Ghent University IMEC, Gent Belgium, 2 Physics and Chemistry of Nanostructures, Inorganic and Physical Chemistry Departement, Ghent University, Gent Belgium, 3 Center for Nano- and Biophotonics (NB-Photonics), Ghent University, Gent Belgium
Recent advances in colloidal nanocrystal synthesis have extended the material’s library greatly to more complex colloidal heterostructures. These new heterostructures are engineered to solve intrinsic problems of colloidal quantum materials, such as ultrafast multiexciton Auger recombination and overall material stability. These new properties, together with their ease of production and processing, and the tunability of their optical properties, make them excellent candidates to render passive integrated photonic devices on silicon-on-insulator, silica and silicon nitride, active. In this work, we present an extensive study of hybrid silicon nitride colloidal nanocrystal device integration. We report on the process optimization for fabricating hybrid waveguides and microdisks and prove the versatility by applying visibly-emitting ‘giant’ dot-in-dot CdSe/CdS/ZnS, CdSe/CdS dot-in-rod and near-infrared emitting PbSe/CdSe and PbS/CdS dot-in-dot. We report on the optical and chemical stability of these materials throughout the processing and investigate the optical performance of the hybrid waveguides and resonators.
K5: Photonics IV
Tuesday PM, November 29, 2011
Independence E (Sheraton)
2:30 PM - K5.1
Strong Multimode Photonic Microresonator and Nanoparticle Interactions.
Yasha Yi 1 2 , Patricia Pignalosa 1 Show Abstract
1 , NYU and CUNY, New York City, New York, United States, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
We have demonstrated strong multimode photonic microresonator and nanoparticle interactions by using an integrated micro disk resonator from through port of the laser coupling bus waveguide. In addition to the fundamental resonance mode, disk resonator has higher order resonance modes. The excited higher order mode has a node at the position where the electromagnetic energy of the fundamental mode is close to a maximum. Here we report that a self referencing mechanism can be achieved by simultaneous excitation of both fundamental and 2nd order micro disk optical resonance modes. Additionally, we are able to measure the area around the maximum of the fundamental resonance mode and the node of the higher order mode, which have overlaps in the disk. In this work, we used on chip disk microresonator as the example, as a variety of types of optical microresonators have been investigated; we used nanoparticle to interact with the two optical resonance modes excited by the coupling bus waveguide, where the nanoparticle can be either dielectric materials or metallic materials. The strong photonic microresonator and nanoparticle interactions has variety of applications for optical switches, waveguides and detection. The self-referencing characteristics of the two optical resonance modes have potential to achieve photonic functions independent of external perturbation, such as temperature change.
2:45 PM - K5.2
Highly Efficient Double-Doped Solid-State White Light-Emitting Electrochemical Cells.
Chih-Teng Liao 1 , Yu-Chun Shen 1 , Hsiao-Fan Chen 2 , Hai-Ching Su 1 , Ken-Tsung Wong 2 Show Abstract
1 Institute of Lighting and Energy Photonics, National Chiao Tung University, Tainan Taiwan, 2 Department of Chemistry, National Taiwan University, Taipei Taiwan
White organic light-emitting diodes (OLEDs) based on polymers and small-molecule materials have attracted intense attention due to their potential applications in flat-panel displays and solid-state lighting. Compared with conventional white OLEDs, solid-state white light-emitting electrochemical cells (LECs) possess several promising advantages. LECs generally require only a single emissive layer, which can be easily processed from solutions, and can conveniently use air-stable electrodes. The emissive layer of LECs contains mobile ions, which can drift toward electrodes under an applied bias. The spatially separated ions induce electrochemical doping (oxidation and reduction) of the emissive materials near the electrodes, i.e. p-type doping near the anode and n-type doping near the cathode. The doped regions induce ohmic contacts with the electrodes and consequently facilitate the injection of both holes and electrons, which recombine at the junction between p- and n-type regions. As a result, a single-layered LEC device can be operated at very low voltages (close to Eg/e, where Eg is the energy gap of the emissive material and e is elementary charge) with balanced carrier injection, giving high power efficiencies. Furthermore, air-stable metals, e.g. Au and Ag, can be used since carrier injection in LECs is relatively insensitive to work functions of electrodes.In this work, we report highly efficient solid-state white LECs based on a double-doped strategy, which judiciously introduces an orange-emitting guest, [Ir(ppy)2(dasb)]+(PF6-) (where ppy is 2-phenylpyridine and dasb is 4,5-diaza-9,9’-spirobifluorene) into a single-doped emissive layer comprising of an efficient blue-green emitting host, [Ir(dfppz)2(dtb-bpy)]+(PF6-)(where dfppz is 1-(2,4-difluorophenyl)pyrazole and dtb-bpy is [4,4′-di(tert-butyl)-2,2′-bipyridine]) and a red-emitting guest, [Ir(ppy)2(biq)]+(PF6-)(where biq is 2,2′-biquinoline) to improve carrier balance and thus to enhance the device efficiency. Photoluminescence (PL) measurements show that the single-doped (red guest) and the double-doped (red and orange guests) host-guest films exhibit similar white PL spectra and comparable photoluminescence quantum yields while device efficiencies of the double-doped white LECs are twofold higher than those of the single-doped white LECs. Therefore, such enhancement of device efficiency is rationally attributed to improved carrier balance of the double-doped emissive layer. Peak external quantum efficiency and peak power efficiency of the double-doped white LECs reach 7.4 % and 15 lm/W, respectively. These efficiencies are among the highest reported for solid-state white LECs and thus confirm that the double-doping strategy is useful for achieving highly efficient white LECs.
3:00 PM - K5.3
Control of Self-Assembly of Erbium Silicates and Erbium Oxides on Si Wafers for Silicon Photonics.
Hiroo Omi 1 , Takehiko Tawara 1 , Yuji Ueda 1 , Toshiki Makimoto 1 Show Abstract
1 Materials Science Research Labs, NTT Basic Research Labs, Atsugi, Kanagawa, Japan
Erbium-doped nano-scale materials have received much attention due to their great potentials as light emitting materials and for optical light amplifiers on silicon wafers at the telecommunications wavelength. In their application to silicon photonics, it is desirable to locate these materials only on specific areas of silicon wafers. However, previous studies have investigated the fabrication of light-emitting diodes or optical waveguides on a macro scale by using a top-down technology. In order to align the nanostructures only on the desired area, however, it is better to combine self-formation techniques and the top-down technique to attain low-cost throughput. On the other hand, recent progress in the research of rare-earth-doped materials has shown that erbium silicates and erbium oxides and erbium-doped yttrium silicates are good candidates for application as light amplifiers on silicon wafers . In this presentation, we will demonstrate that the self-assembly formation of erbium silicates and erbium oxides can be controlled by lithographical patterning of silicon substrates. Erbium oxides were deposited on intentionally patterned Si substrates by rf-sputtering at room temperature and then annealed in Ar gas ambience at the temperatures below 1200 degrees C. Real-time synchrotron X-ray diffraction, atomic force microscopy, cross-sectional transmission electron microscopy, and micro photoluminescence revealed that crystalline erbium oxides several hundred nanometers in size are preferentially aligned on the area of the line and space mesa and trench patterns and that islands of erbium silicates with nanoscale size are self-assembled on the region of non-patterned Si(111) wafers. The presence of erbium silicates on the non-patterned Si indicates that the thermal annealing produces erbium silicates as a result of the reaction Er2O3 + Si + O2 = Er2SiO5. We also observed 1.5-micrometers photoluminescence of Er3+ ions with clear Stark splits from the self-assembled erbium oxides and erbium silicates, indicating that the crystalline quality is good enough for the applications. Time-resolved PL measurements indicate that the lifetimes of the PL from the transition between 4I(15/2)-4I(13/2) in the erbium oxide and erbium silicate are on the order of 10 micro sec. From the fitting of the decay curves of the erbium oxides with the Burshtein model , we derived the energy transfer interaction parameter γ and the energy migration interaction parameter K to be 188 s^-(1/2) and 1.13×10^4 1/s, which indicate energy migration by hopping plays a very important role in the self-assembled crystals. Additionally, we will also present a method for obtaining single-phase of erbium monosilicates on the planar Si wafers without erbium oxide formation.  S. Sani, K. Chen, X. Duan, J. Michel, L. Kimerling, M. Lipson, J. Elect. Mat. 33, 809 (2004). A. I. Burshtein, Sov. Phys. JETP 35, 882 (1972).
3:15 PM - K5.4
Rabi Splitting of G-Center Emission in Silicon Microdisks.
Lyuba Kuznetsova 1 , Gustavo Fernandes 1 , Jimmy Xu 1 2 Show Abstract
1 , Brown University, Providence, Rhode Island, United States, 2 WCU program, Seoul National University, Seoul Korea (the Republic of)
Microcavity control of Si emissive centers represents a new approach toward turning Si into an optical gain medium. Though G-centers stimulated emission in nanopatterned Si has been demonstrated , but the luminescence in bulk structures is quenched above 80K. The rate of spontaneous emission (SE) can be modified by placing emissive centers inside a microcavity with high quality factor Q. In the weak coupling regime, the Purcell effect can enhance the rate of SE by Fp~ Q , which could potentially enable emission at higher temperatures than presented in . The SE rate could also be enhanced in a subwavength cavity to enable ultrafast modulation at a rate greatly exceeding that of a laser diode. But, in the strong coupling regime, if the coupling strength between emitter and optical cavity exceeds the mean of their decay rates, the coupled system has two eigenenergies—that is, their states split. Here we present a study of coupling the Si G-center emission with a microcavity mode, in an attempt to find conditions for enhancing the emission.The microdisks were fabricated from the carbon enriched nanopatterned SOI (annealed at 650–900°C for 20s-10min) using e-beam lithography (XR-1541 resist) and dry etching (ICP RIE using SF6 and C4F8). Tapered-fiber spectroscopy results show that the free spectral range for the microdisk modes is increased (~ 12%) due to effective refractive index change associated with nano-patterning but the resonances preserve relatively high Q (Q~2500 for the TM1 mode). The temperature dependence of the effective refractive index is used to shift a nearby cavity-mode (TM1,13) into and then away from the G-center line.The PL measurements for the bulk control samples show that the intensity of the G-line (1278 nm) is stronger for samples with shorter annealing times but it still decreases with the temperature as expected . Direct optical pumping of the microdisk (using Ar laser at 514 nm) shows that as the cavity mode wavelength shifts with increasing temperature, the coupling between the G-line and the cavity mode could be strong enough to give rise to a prominent spectral splitting (Rabi splitting). The splitting, twice the emitter-field coupling strength, is estimated 2g ~ 0.92THz (~5nm) (G-center radiative decay time ~8µs ). From this estimate, g satisfies the strong coupling condition g>κ/4 for the cavity decay rate κ = 0.094 THz.It is both interesting and revealing that Rabi splitting could occur before the benefit of Purcell enhancement is realized in the presence of strong coupling between a point (molecular) emitter and a high Q microdisk mode. Although the experiment is specific to the zero-phonon G-center emission in Si, its finding is generally relevant to molecular emitters in a cavity.  S.Cloutier, P.Kossyrev, J.Xu, Nature Materials 4, 887 (2005) E.M. Purcell, Phys. Rev.69, 681 (1946) G.Davies, H.Brian, E.Lightowlers, K.Barraclough, and M.Thomaz, Semicond. Sci. Technol.4, 200 (1989)
4:00 PM - K5.5
Heat Conduction and Photoluminescence in Silicon Nitride Films.
Amy Marconnet 1 , Matthew Panzer 1 3 , Selcuk Yerci 2 , Luca Dal Negro 2 , Kenneth Goodson 1 Show Abstract
1 Mechanical Engineering, Stanford University, Stanford, California, United States, 3 , KLA-Tencor, Milpitas, California, United States, 2 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States
Silicon-rich silicon nitride is a promising candidate for silicon-compatible active and passive photonic devices due to its light emitting properties and relatively high refractive index. However, the variation of optical, electrical, and thermal properties and the trades-off between them with the amount of excess silicon and annealing conditions have not been comprehensively studied. In this study, the thermal conductivity and photoluminescence lifetime of silicon-rich silicon nitride films are measured across a range of silicon concentrations and annealing conditions using time-domain picosecond thermoreflectance and time-resolved photoluminescence. A significant correlation between these properties suggests that the microstructure of the amorphous silicon nitride film strongly influences both properties. The samples with long photoluminescence lifetimes also possess the high thermal conductivities. We show that low excess silicon concentrations and high annealing temperatures are required to obtain the highest thermal conductivity and the best emission efficiency at the same time. This work explores the idea that controlling the microstructure is the key to yielding effective CMOS-compatible light sources from this class of materials.
4:15 PM - K5.6
Optical Coatings Utilizing Nanoporous Thin Films Fabricated on Flexible Polymer Substrates.
David Poxson 1 4 5 , Frank Mont 6 , Jaehee Cho 3 5 , E. Fred Schubert 3 4 5 , Richard Siegel 2 4 Show Abstract
1 Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 4 Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute, Troy, New York, United States, 5 Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, New York, United States, 6 , Raydex Technology, Inc, Cambridge, Massachusetts, United States, 3 Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Nanoporous thin films have been reported on for over a century and have been studied extensively. One reason for this considerable interest is that nanoporous coatings have been shown to have novel physical properties that can depart greatly from their dense counterparts. In addition, such coatings are particularly promising owing to their optical property tailorability. By controlling the detailed structural characteristics of such nanoporous films, their optical properties may be arbitrarily tailored and customized within a range of desired values to be responsive to application-specific requirements, and are capable of excellent optical performance. Examples of such tailorability include: density, refractive index, electrical and thermal conductivity, absorption, and polarization. However, due to the challenges of fabricating nanoporous optical coatings, such coatings have been almost solely fabricated on rigid planar substrates. By limiting the fabrication of nanoporous optical coatings to rigid and flat surfaces, the list of potential applications is greatly reduced. Here we report on the design and fabrication of high performance optical coatings utilizing nanoporous thin films on flexible polymer substrates. These optical coatings utilize both single- and multi-layer tailored nanoporous thin films and are fabricated using oblique-angle electron-beam deposition. Anti-reflection and high-reflection optical coatings have been fabricated on planar polymer substrates and subsequently bent or molded into various three dimensional shapes. We demonstrate that these nanoporous SiO2 and TiO2 optical coatings have good adhesion characteristics on a variety of polymer substrates, and can be molded, bent, shrunk and stretched while closely maintaining their designed structural and optical properties. The ability to fabricate nanostructured coatings on flexible and three dimensional surfaces significantly expands the list of available applications that can benefit from such coatings. Applications can include: flexible solar cells and displays, optical sensors, fiber-optic communication devices, as well as high performance lenses, mirrors and spectral filters. Additionally, the ability to design and fabricate nanoporous coatings on flexible, mold-able, elastic polymer substrates potentially introduces important new functionalities previously unavailable to nanoporous coatings on traditional flat and/or rigid substrates. As an example, it is possible to tune the optical properties of a nanostructure, in real-time, by controlled stretching, shrinking, or bending of the flexible substrate. The broader range of applications for nanoporous coatings, as well as their new functionalities has the potential to open up entirely new areas of nanostructured coating research.
4:30 PM - K5.7
Efficient Host-Guest Solid-State Light-Emitting Electrochemical Cells with Improved Balance of Carrier Mobilities.
Chih-Teng Liao 1 , Hsiao-Fan Chen 2 , Hai-Ching Su 1 , Ken-Tsung Wong 2 Show Abstract
1 Institute of Lighting and Energy Photonics, National Chiao Tung University, Tainan Taiwan, 2 Department of Chemistry, National Taiwan University, Taipei Taiwan
Solid-state light-emitting electrochemical cells (LECs) possess several advantages over conventional organic light emitting diodes (OLEDs). In LECs, electrochemically doped regions induced by spatially separated ions under a bias form Ohmic contacts with electrodes, giving balanced carrier injection, low operating voltages, and consequently high power efficiencies. As such, LECs generally require only a single emissive layer, which can be easily processed from solutions and can conveniently use air-stable electrodes, while OLEDs typically require more sophisticated multilayer structures and low-work-function cathodes. Compared with conventional polymer LECs composed of an emissive conjugated polymer, a salt and an ion-conducting polymer, LECs based on cationic transition metal complexes (CTMCs) show several further advantages. In such devices, no ion-conducting material is needed since these CTMCs are intrinsically ionic. Furthermore, higher electroluminescent (EL) efficiencies are expected due to the phosphorescent nature of CTMCs.In general, CTMC-based LECs are composed of neat films of emissive materials, which often suffer self-quenching induced by interactions between closely packed molecules. Therefore, to further reduce self-quenching and increase EL efficiency, we report efficient host-guest solid-state LECs utilizing a blue-emitting ionic small-molecule fluorene derivative (Fan13) as the host and a red-emitting CTMC (Fan7) as the guest. Carrier trapping induced by the offset in the lowest unoccupied molecular orbital (LUMO) levels between the host and the guest impedes electron transport in the host-guest films and thus improves balance of carrier mobilities of the host films intrinsically exhibiting electron preferred transporting characteristics. Photoluminescence measurements show efficient energy transfer in this host-guest system and thus ensure predominant guest emission at low guest concentrations, rendering significantly reduced self-quenching of guest molecules. EL measurements show that the peak EQE (power efficiency) of the host-guest LECs reaches 3.62% (7.36 lm/W), which approaches the upper limit that one would expect from the photoluminescence quantum yield of the emissive layer (~0.2) and an optical outcoupling efficiency of ~20% from typical layered structure and consequently indicates superior balance of carrier mobilities in such host-guest emissive layer. These results are among the highest reported for red-emitting LECs and thus confirm that in addition to reducing self-quenching of guest molecules, the strategy of utilizing a carrier transporting host doped with a proper carrier trapping guest would improve balance of carrier mobilities in the host-guest emissive layer, offering an effective approach for optimizing device efficiencies of LECs.
4:45 PM - K5.8
High Performance Quasi-Solid-State Dye-Sensitized Solar Cells with a Light Trapping Polymer Gel Electrolyte.
Woosung Kwon 1 , Shi-Woo Rhee 1 Show Abstract
1 Chem. Eng., Pohang University of Science and Technology, Pohang Korea (the Republic of)
Dye-sensitized solar cells (DSCs) have received much attention as promising candidates for low-cost and large-area photovoltaic applications. In order to achieve efficiencies over 10%, light scattering layers have been used conventionally for efficient light harvesting. They ascertain recapture of unabsorbed light, which otherwise will be lost due to transparency of the TiO2 layer. In pursuit of practical application, however, DSCs are moving for compactness and flexibility. In most cases, light scattering layers require several time and cost consuming steps additionally. Also, they result in thicker photoanodes and poor adhesion to the transparent TiO2 layer of different particle radii, where both cause cracks during sintering or under bending. In this research, light trapping polymer gel electrolytes (LT-PGEs) were prepared in order to avoid the problems stemming from the light scattering layer without sacrificing the light harvesting efficiency. For the purpose, hierarchically structured TiO2 microspheres were synthesized and incorporated into PGEs based on poly(lactic acid-co-glycolic acid) (PLGA). These microspheres exhibit strong scattering properties in the visible light region and possess nanometer-sized pores to facilitate the ion diffusion in the electrolyte. Also, PLGA is a linear amphiphilic copolymer and widely used to deliver biomedical drugs due to its good mechanical properties, low toxicity, and structural amorphousness. The polymer chains help the TiO2 microspheres disperse in the electrolyte without precipitation, and further retain a solvent to prevent evaporation. The LT-PGE renders more efficient light harvesting than conventional scattering layers so that can show high efficiencies of 8.2% in comparison with the liquid electrolyte of 7.7%. In view of long-term stability, the efficiencies lie in ±10% of the initial value during 1500 h under ambient conditions. The LT-PGE can realize a compact photoanode excluding conventional light scattering layers, and grant dye-sensitized solar cells (DSCs) compactness, flexibility, and long-term stability. Thus, the LT-PGE would foster large scale production such as a roll-to-roll process and practical application of DSCs.
5:00 PM - K5.9
Metallic Trench Resonator for Enhanced Spontaneous Emission of Nano-Crystals.
Tsung-li Liu 1 , Kasey Russell 1 , Evelyn Hu 1 Show Abstract
1 School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, United States
Microcavities with high quality factor (Q) and small mode volume (V) have been used to enhance interaction between light and matter. Recently, it has been reported that metal-based optical cavities can show high values of Q/V and therefore achieve strong light-matter interaction. This result is somewhat counter-intuitive because metal-based optical cavities have inherently low values of Q because of resistive losses in the metal. High values of Q/V can nevertheless be achieved through the design of cavities with very small mode volume. Despite the promise of metal-based optical cavities, experimental realization of such cavities is difficult because of their extreme sensitivity to fabrication imperfections such as surface roughness. Here we present the fabrication and characterization of one-dimensional photonic crystal nanocavities formed using metallic slot waveguides in a silver film. Using focused ion beam (FIB), trenches were etched onto a template-stripped silver surface. Periodic modulations of the trench width act as Bragg reflectors for confinement along the cavity axis. Finite difference time domain (FDTD) simulations of the structure show distinct resonating modes. After cavity fabrication, fluorescent colloidal nanocrystals are deposited into the trench and couple strongly with the cavity modes. An important feature of our cavities is that optical emitters can be coupled to the maximum of the cavity mode after the cavity fabrication is complete. This prevents fabrication-induced damage of the optical emitters and makes it possible to couple a wide range of optical emitters to the cavity. Photoluminescence results show that the emitter fluorescence is strongly modified by the cavity modes and that the mode wavelength varies deterministically with the pitch of the photonic crystal. Confocal fluorescence microscopy maps show the mode is strongly localized in the cavity, as expected from FDTD simulations. Finally, we present time-resolved fluorescence measurements of the effect of the cavity modes on the spontaneous emission lifetime of the nanocrystals.
5:15 PM - K5.10
Level Set Photonic Quasicrystals with Phase Parameters.
Lin Jia 1 , Ion Bita 2 , Edwin Thomas 1 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 , Qualcomm MEMS Technologies, San Jose, California, United States
We report the first systematic study of the photonic band gap (PBG) properties of 10- and 12-fold rotational symmetric quasicrystals (QCs) defined by level set equations with various phase parameters. The optimized filling ratios corresponding to the largest transverse magnetic (TM) PBGs for 18 types of QCs are found, which are useful for photonic QC fabrication design. The impact of filling ratio, rotational symmetry, and experimental fabrication parameters on the resultant TM PBGs are explored via PBG maps. We also demonstrate large area, high quality 8-, 10-, and 12-fold quasicrystalline pattern fabrication using multiple exposure interference lithography (MEIL).
5:30 PM - K5.11
Polymeric Concave Bragg Reflectors Fabricated Using Optical Lithography.
Ke Liu 1 , Huina Xu 1 , Qiaoqiang Gan 1 , Alexander Cartwright 1 Show Abstract
1 Department of Electrical Engineering, State University of New York, University at Buffalo, Amherst, New York, United States
Polymeric distributed Bragg reflectors are of interest in microscopic biosensing, cell trapping, micro-electro-mechanical-systems (MEMS) and optoelectronics because of its ability to selectively reflect and focus a parallel beam of incident light matching its photonic bandgap. Here, we report the fabrication of polymeric concave Bragg reflectors that can be assembled into a large area concave micro Bragg reflector array. These structures are produced by using self-assembly of colloidal spheres in an optical lithography technique that results in a rapid low-cost process. We will present simulations that show that a concave microscale Bragg reflector can be well formed around the colloidal spheres. The self-assembly of microspheres forms a well-aligned microsphere array on a pre-cleaned glass slide. The microspheres are then capped with a 100nm silver layer to form a convex shaped reflector array. Subsequently, a pre-polymer syrup containing a volatile solvent, monomer, a photoinitiator, and co-initiator is sandwiched between the microsphere array and a glass slide. Photopolymerization is initiated using reflection holography with a 532nm laser light. Subsequent UV curing results in well-defined lamellae of the polymer separated by porous polymer regions that create a high quality concave shaped polymer Bragg reflector array. The light profile in free space is characterized and demonstrates the ability to reflect and focus selective bands of wavelengths. Combined with florescent agents, the Bragg reflector arrays can greatly enhance the collection efficiency of fluorescence by directing collected signals to a detector. Compared to porous silicon multilayered reflector using standard photolithography, the holography lithography is a simple and inexpensive way to fabricate large area Bragg reflectors. Development of such microstructures opens up new applications in optical sensing and spectroscopic imaging.
5:45 PM - K5.12
Annealing Enhanced Photoluminescence in Er-Doped TeO2.
Michiel Vanhoutte 1 , Pao-Tai Lin 1 , Vivek Singh 1 , Anu Agarwal 1 , Lionel Kimerling 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Erbium doped tellurite (Er-TeO2) is an especially promising material system for Si-CMOS-compatible microphotonics because of the high solubility of erbium in TeO2. Due to the heavy ions Te4+ and O2-, the refractive index is higher (n = 1.9-2.2) and the maximum phonon energy is lower (<800cm-1) than in Si-O based materials. This allows for the design of compact microphotonic devices and yields a larger emission cross-section, a faster radiative decay and a less efficient non-radiative decay than traditional materials doped with erbium. Additionally, Er-TeO2 thin films are transparent from the visible to mid-IR spectrum, which makes them suitable for ultra-broad band integrated photonics.We demonstrate the successful deposition of transparent Er-TeO2 thin films deposited on Si by room temperature reactive RF-magnetron co-sputtering of Er and TeO2 in Ar/O2 plasma. After deposition, the films are for 1h in O2, at temperatures between 300C and 900C. The films show strong photoluminescence (PL) around 1.54μm when the Er ions are excited with 488 nm argon laser light. We observe an enhancement of the PL intensity by annealing at 300C and 600C. In fact, the PL intensity increases with a factor 98 between the as-deposited film and the film annealed at 600C. This observation is in line with the expectation that an annealing step will cause optical activation of the Er3+ ions and will reduce defects causing non-radiative de-excitation paths. As a consequence, the internal quantum efficiency for photoluminescence increases with annealing temperature. The tremendous enhancement can also be attributed to crystallization of the film at 600C. Whereas the film annealed at 300C is amorphous, the film at 600C crystallizes into a tetragonal TeO2 phase with space group P41212 (pdf reference card 8-0484). The relation between PL and crystallinity is in line with the observation that several sharp peaks develop in the PL spectra of the films annealed at temperatures above 600C. This indicates a reduction in inhomogeneous broadening of the Er3+ PL, due to a homogenization of the Er3+ environment. The PL intensity of the film annealed at 900C is comparable to the PL intensity of the as-deposited film. We attribute this decrease in PL to clustering of Er ions, which quenches luminescence efficiency.The influence of oxide composition on crystallization temperature and on photoluminescence properties is investigated. Application of Er-TeO2 in CMOS compatible photonic devices is demonstrated.
Thomas M. Cooper Air Force Research Laboratory
Steven R. Flom Naval Research Laboratory
Michael Bockstaller Carnegie Mellon University
Cesar Lopes Swedish Defence Research Agency (FOI)
K6/CC7: Joint Session
Wednesday AM, November 30, 2011
Room 207 (Hynes)
9:30 AM - K6.1/CC7.1
ENZ-Enhanced Transmission through a Subwavelength Slit.
Sandeep Inampudi 1 , David Slocum 1 , David Adams 1 , Shiva Vangala 1 , Nicholas Kuhta 2 , William Goodhue 1 , Daniel Wasserman 1 , Viktor Podolskiy 1 Show Abstract
1 Physics and Applied Physics, University Of Massachusetts Lowell, Lowell, Massachusetts, United States, 2 Department of Physics, Oregon State University, Corvallis, Oregon, United States
Efficient transmission of light through device structures with subwavelength openings has numerous practical applications in the fields of optical communication, subwavelength imaging and lithography. One approach to enhance the transmission efficiency through subwavelength structures relies on periodically modulated plasmonic systems on composite-based structures, which is often accompanied with substantial fabrication challenges. A promising alternative mechanism to achieve enhanced transmission through subwavelength regions involves materials with vanishingly small dielectric permittivity, also known as epsilon-near-zero (ENZ) materials. A single flat layer of ENZ-material is expected to provide efficient coupling between free-space radiation and sub-wavelength guiding structures. In this work we performed a comprehensive analysis of the role of ENZ materials in the enhancement of light transmission through a subwavelength slit. We have experimentally verified the enhanced transmission through the bulk ENZ material at optical frequencies and developed an analytical model capable of calculating the field distribution throughout the system. Our results show that the transmission enhancement is dominated by the plasma resonance of ENZ coupling layer. In the limit of extremely small material absorption, the overall transmission can be further enhanced by filling the inside of the slit with ENZ medium. In realistic plasmonic systems, however, transmission enhancement due to ENZ filling of the slit needs to be weighed against material absorption accompanying the plasma resonance.
9:45 AM - K6.2/CC7.2
Vertical and Lateral Gap Mode Plasmonic Cavities with Coupled Organic Gain Medium.
Shanying Cui 1 , Kasey Russell 1 , Tsung-li Liu 1 , Evelyn Hu 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Surface plasmon polaritons concentrate optical energy to sub-wavelength length scales, leading to considerable interest in nanoscale metal devices. Metal-based cavities that concentrate electromagnetic fields in the vicinity of optical emitters are of particular interest for investigations into quantum electrodynamics. Although metal losses limit the maximum cavity quality (Q) factors in metal-based cavities, the much smaller mode volumes (V) in these structures provide a Q/V comparable to that of dielectric cavities. We have tested the limits of small mode volumes with two different plasmonic nanocavity geometries: a vertical and horizontal one. The vertical cavity consists of a silver nanowire lying parallel to a silver substrate. The lateral cavity is a narrow trench milled into a silver substrate. In this report, we explore the use of use organic emitters in both geometries. An important advantage of these metal cavities is the wide choice of optically active layers that may be incorporated into the device. Our group has recently demonstrated colloidal PbS nanocrystal coupled to the vertical cavity. Quantum dots, however, are typically several nanometers in diameter, and their incorporation within cavities requires care to achieve thin layers with uniform thicknesses that can effectively couple to the cavity modes. Fluorophores, a class of organic dyes, can be covalently bound as a thin, conformal monolayer to fit in small gaps. They are ubiquitous, versatile and easily functionalizable for further applications, such as single-molecule detection or biosensing. In order to have ultrathin gaps in the cavities with controlled modes and maximized electromagnetic fields, it is imperative to have ultrasmooth silver surfaces. Silver substrates with sub-nanometer roughness is achieved through a ‘template stripping’ method. A thin film of silver is deposited onto an atomically-smooth Si wafer and subsequently transferred to another substrate. In the lateral gap mode cavities, the smooth surfaces are a result of careful optimization of the focused ion beam milling used to form the trenches. In both the vertical and lateral cavity geometries, the coupled gain medium is a self-assembled monolayer of fluorophore dye in the gap, either between the nanowire and the substrate, or within the trench between two metal surfaces. A thin layer of dielectric is deposited through atomic layer deposition between the metal surfaces and the dye to prevent metal quenching of the dye emission. We have observed clear peaks on the dye emission spectrum, evidence of fluorescence coupled to the modes of the cavity, in both cavity geometries. The gap size and trench depth are essential variables to understanding the limits to our system. Organic dyes give us the capability to explore these limits by controlling the gap thicknesses with layer-by-layer growth or by binding it to molecules self-assembled on thickness controlled atomic layer deposition of dielectrics.
10:00 AM - K6.3/CC7.3
Demonstration of a SPASER Mechanism by the Coupling of Diamond and Plasmonic Au Nanoparticles.
Silvia Orlanducci 1 , Ilaria Cianchetta 1 , Emanuela Tamburri 1 , Valeria Guglielmotti 1 , Francesco Toschi 1 , Massimiliano Lucci 2 , Maria Letizia Terranova 1 Show Abstract
1 Dip. di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Roma Italy, 2 Dip. di Fisica, Università di Roma Tor Vergata, Roma Italy
The coupling of diamond color centers with surface plasmons (SP) and/or structures represents an interesting field of research in solid state physics, material science, and nanophotonics.The basic idea underlying the present research is the coupling of Si optical centers of various diamond systems with plasmonic Au nanoparticles in a SPASER (short for Surface Plasmon Amplification by Stimulated Emission of Radiation) configurations. SPASER, one of the most attractive and recent concept in nanophotonic, it is a synergic process occurring when a resonance between SP and the emission from an active medium (named gain) is achieved. The emission properties of the gain and the SP modes define the SPASER’s working frequency, which are completely unrelated to the used excitation field energy . SPASER was theoretically introduced for the first time by Bergman & Stockman in 2003 , whereas first experimental demonstration was only found in 2009 with the work of Noginov’s group . In the frame of Stockman’s theory, in our labs the issue of producing systems suitable for the spasing mechanism has been addressed by coupling diamond Si color centers with properly designed plasmonic Au nanoparticles. A high concentration of Si defects in the diamond lattice is achieved by inserting Si nanoparticles during the CVD growth of diamond , whereas size-controlled Au nanoparticles are produced using chemical routes. In our experiments the excitation of the diamond photoluminescence (PL) Si defects (emission at 738 nm) is provided by a laser line at 514 nm, whereas the Au surface plasmons have a maximum in the absorption spectrum at 740 nm perfectly coupled with the 738 nm PL band.The resonant energy transfer from the excited diamond defects to the gold plasmonic modes able to locally enhance the Si photoluminescence (PL), the threshold behavior of the PL enhancement vs pumping energy, the decrease of the FWHM of PL with increasing the pumping laser energy, represent as a whole the first experimental evidence of an efficient SPASER mechanism provided by a diamond-based system .The relevant spasing performance demonstrated by our diamond-Au samples, characterized by the stability and the chemical inertness of an all solid-state source, opens an exciting prospective for the development of novel nanophotonic devices .Bergman, D. J. & Stockman M., Phys. Rev. Lett. 90, 027402, (2003) Noginov, M. A., Nature, 460, 1110-1112, (2009) Orlanducci, S. et al., Surface & Coatings Technology 201, 9389–9394, (2007) Orlanducci, S., Cianchetta, I., Tamburri, E., Guglielmotti, V., Terranova, M.L., Nature Photonics, under consideration
10:15 AM - K6.4/CC7.4
Correlated Optical Measurements and Plasmon Mapping of Metallic Nanostructures.
Beth Guiton 1 2 , Vighter Iberi 3 , Shuzhou Li 4 , Donovan Leonard 2 5 , Chad Parish 2 , Paul Kotula 6 , George Schatz 7 , Stephen Pennycook 2 8 , Jon Camden 3 Show Abstract
1 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Chemistry, University of Tennessee, Knoxville, Tennessee, United States, 4 Division of Materials Science, Nanyang Technological University, Singapore Singapore, 5 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 6 Materials Characterization Department, Sandia National Laboratories, Albuquerque, New Mexico, United States, 7 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 8 Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, United States
Plasmonics is a rapidly growing field with applications spanning communications, computing, photovoltaics, sensors and medical diagnosis. The continuing trend toward increasing complexity and reduced size makes imaging of the plasmonic modes extremely challenging. We will show how spatial maps of the localized surface plasmon (LSP) modes of high-aspect-ratio silver nanorods can be directly obtained using electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM), and correlated for the first time to optical data from the exact same particles. Multivariate statistical analysis (MVSA) enables the extraction of both dark and light modes, which show excellent agreement with classical electrodynamics calculations of the near-electric-field enhancements obtained from planewave excitation. EELS mapping is thus demonstrated to be an invaluable technique for elucidating complex and overlapping plasmon modes. As such this result should have a powerful impact on the growing nano-plasmonics and related energy research communities.
11:00 AM - K6.5/CC7.5
Surface Plasmon and Photonic Mode Propagation in Gold Nanotubes with Wall Thickness on the Order of the Electron Mean Free Path.
Jesse Kohl 1 , Deirdre O'Carroll 2 Show Abstract
1 Materials Science and Engineering, Rutgers University, Piscataway , New Jersey, United States, 2 2.Department of Chemistry and Chemical Biology and IAMDN, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States
Large inner diameter (ID, 200 nm) gold nanotubes (AuNT’s) were synthesized to study the optical properties and surface plasmon polariton (SPP) mode propagation as function of wall thickness (WT), excitation angle and polarization direction. Fabrication was carried out using nanoporous alumina templates which yield ~30 mm2 arrays with ~108 AuNTs with WT tuned from 30 nm to > 140 nm. Dark-field spectroscopy of nanotube arrays and single nanowire/nanotube heterostructures show a red shift (> 100 eV) over this WT range. Finite-difference-time-domain simulations of AuNT’s of constant 200 nm ID and WT of 30, 60 and 140 nm exhibit red shifts of 63 and 128 eV under axial and normal excitation, while exhibiting SPP propagation lengths of 0.40, 1.15 and 1.30 µm under 660 nm excitation and 1.1, 2.2 and 2.0 µm under 770 nm excitation for the three WT’s, respectively. The AuNT’s also exhibit photonic mode propagation which increases with increasing WT and longer excitation wavelengths (2 µm under 660 nm excitation and 4.7 µm under 770 nm excitation for ID = 140 nm). Increasing SPP and photonic mode propagation length is attributed to the WT becoming greater than the bulk electron mean free path for gold (38 nm), resulting in sufficient electron density to confine and propagate higher energy modes. Thinner structures can only support lower energy modes excited by longer wavelengths which results in the apparent red shift. Electric-field intensity profiles show inter-wall coupling, analogous to insulator-metal-insulator waveguides only under normal excitation. Axial excitation results in SPP mode propagation on the outer surface but no inter-wall coupling. With suitable choice of WT, AuNT’s may be employed for anisotropic light confinement and large-area arrays of vertically aligned waveguides or optical cavities.
11:15 AM - K6.6/CC7.6
Hybrid Optoplasmonic Elements and Materials for High-Performance Optical Information Processing and Sensing.
Svetlana Boriskina 1 , Wonmi Ahn 1 , Yan Hong 1 , Bjoern Reinhard 1 Show Abstract
1 Chemistry Department, Boston University, Boston, Massachusetts, United States
Noble-metal nanostructures that support localized surface plasmon (SP) resonances offer unsurpassed capabilities for sub-wavelength light focusing and high sensitivity to environmental changes, which explains their rapidly expanding role in nanoimaging and biomedical research. While spectral positioning of the localized SP resonances can be achieved by varying nanoparticles morphology, dissipative losses in metals hinder efficient control over SP resonances linewidths. These losses also limit the use of propagating SP polaritons as the long-distance signal carriers and challenge the construction of extended functional plasmonic nanocircuits. Finally, development of robust schemes for active nanoscale field modulation, frequency switching, and reversible energy transfer between photons, SPs and nanoscale emitters is stifled by fundamental restrictions on scaling existing tuning mechanisms to nanoscale dimensions.To address these challenges, we have recently proposed hybrid optoplasmonic structures that combine the capability of optical microcavities to insulate emitter-photon systems from decohering environmental effects with the superior nanofocusing properties of SP nanostructures . Efficient photon trapping and re-cycling in photonic microcavities provides mechanisms of strong spectral selectivity in the proposed optoplasmonic elements and strong resonant modification of radiative rates of embedded emitters . We will show that novel classes of optoplasmonic amplifiers and frequency (de)multiplexers can be realized through tailored coupling of optoplasmonic elements into discrete networks . We will demonstrate the capability of optoplasmonic circuits to enable adaptive light switching on nanoscale and active control over cascaded photon-emitter interactions over both short (nanometers) and long (hundreds of microns) length scales [1,2]. Finally, we will highlight the opportunities of hybrid optoplasmonic structures as biosensing platforms that combine high sensitivity of plasmonic elements with high spectral resolution of high-Q microcavities and thus can feature improved detection limits as compared to individual photonic and plasmonic sensors . While this paper focuses on theoretical concepts of optoplasmonic elements and networks, recent advances in nanofabrication technologies put the fabrication of these structures within reach, and we will briefly discuss the available fabrication strategies for practical realization of hybrid resonant optoplasmonic structures developed in our group  and elsewhere.  S.V. Boriskina & B.M. Reinhard, Proc. Natl. Acad. Sci. USA 108(8), 3147-3151 (2011). S.V. Boriskina & B.M. Reinhard, Opt. Express, Focus Issue Collective Phenomena in Photonic, Plasmonic and Hybrid Structures (S.V. Boriskina et al Eds.) (2011). M.A. Santiago-Cordoba, S.V. Boriskina, F. Vollmer & M.C. Demirel, Appl. Phys. Lett. Aug (2011). W. Ahn, S.V. Boriskina, Y. Hong & B.M. Reinhard, submitted to Symposium CC
11:30 AM - K6.7/CC7.7
Epsilon near Zero Material with Ag/TiO2 Composite.
Ganapathi Subramania 1 , Arthur Fischer 1 Show Abstract
1 , Sandia National Laboratory, Albuquerque, New Mexico, United States
Epsilon near zero (ENZ) materials are metamaterials whose effective dielectric permittivity (epsilon) is close to zero for a wavelength range of interest. This results in unique electromagnetic properties such as unusually large effective wavelength inside the medium even at optical frequencies, important for nanoscale optical circuits. Such materials can be achieved utilizing metal-dielectric multilayer composites which provide the negative and positive components of the dielectric permittivity respectively, needed to achieve an effective near zero value. The small values of epsilon near the ENZ wavelength also makes them attractive for enhancing non-linear behavior by utilizing the non-linearity of metals. Large changes in transmission with low power inputs have been predicted for such systems[2, 3] leading to interesting optical bistability behaviors. Silver (Ag) is an attractive option as it has high non-linear coefficient (3.16 × 10−16 m2/V2) while having a high plasma frequency. We will describe a metal-dielectric multilayer composite consisting of Ag and titanium dioxide (TiO2) fabricated using electron beam evaporation to achieve an ENZ behavior near 630nm wavelength . The typical thicknesses of Ag and TiO2 are kept around 15-20nm and 45-55nm respectively. High dielectric constant of TiO2 enables keeping the layer thicknesses small in order to minimize non-local effects that can adversely affect effective medium behavior. We will discuss the optical transmission and effective dispersion response of the composite structure obtained through spectroscopic and interference measurements. We will also discuss the effective non-linearity of the Ag/ TiO2 composite as well as the role of metal losses.Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.References:N. Engheta, Science 2007, 317, 1698.A. Husakou, J. Herrmann, Phys. Rev. Lett. 2007, 99, 127402.N. N. Lepeshkin, A. Schweinsberg, G. Piredda, R. S. Bennink, R. W. Boyd, Phys. Rev. Lett. 2004, 93, 123902.A. Ciattoni, C. Rizza, E. Palange, Physical Review A 2011, 83, 043813.
11:45 AM - K6.8/CC7.8
Third-Order Nonlinear Optical Properties of Uniaxial Metal-Dielectric Composites.
Joseph Geddes 1 2 , Erik Nelson 3 , Paul Braun 1 2 Show Abstract
1 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
We show how uniaxial composites comprising alternating thin planar subwavelength layers of metal and dielectric materials can exhibit third-order optical nonlinearities greater than those of the already large intrinsic nonlinearities of the metal, when the appropriate volume fraction of metal is chosen. The enhancement occurs in the direction perpendicular to the plane of the layers. Furthermore, the absorption in these materials could be limited or even less than that of the bulk metal component in some cases. We report z-scan measurements of the nonlinear refractive index of several such composites.
12:00 PM - K6.9/CC7.9
Mode Matching Analysis for Negative Refraction in a Two Dimensional Plasmonic Metamaterial.
Sandeep Inampudi 1 , Igor I Smolyaninov 2 , Viktor Podolskiy 1 Show Abstract
1 Physics and Applied Physics, University Of Massachusetts Lowell, Lowell, Massachusetts, United States, 2 Department of Electrical and Computer Engineering, University of Maryland, College Park, Maryland, United States
The phenomenon of negative refraction, well understood in homogeneous magnetic or anisotropic systems remains a mystery in planar plasmonic metamaterials formed by periodic arrays of thin PMMA ridges deposited on metal substrate. Up to date there exists at least two different theoretical explanations for this phenomenon, one based on the energy-momentum directions of the SPP at the single metal-dielectric interface, and the other based on Dyakonov waves. However, neither of these explanations accounts for the complex three-dimensional geometry of the system and the non-trivial coupling between SPPs and free-space modes associated with this geometry. Here we present a theoretical analysis of this phenomenon of negative refraction of surface plasmons in planar plasmonic metamaterials. We use mode matching technique to analyze the dynamics of the plasmonic mode and its non-trivial coupling to the free space waves and to the other guided modes of the system, taking into account the extended 3D-geometry and the finite thickness of the PMMA ridges. The eigen states of the periodic system dominated by the surface waves are identified and their dispersion is analyzed via generalization of mode-matching formalism and Bloch-periodic approach.
12:15 PM - K6.10/CC7.10
Mode Engineering with Organic Microcavities Using Thin Metal Layers.
Susanne Hintschich 1 , Alexander Zakhidov 1 , Robert Brueckner 1 , Markas Sudzius 1 , Hartmut Froeb 1 , Vadim Lyssenko 1 , Karl Leo 1 Show Abstract
1 , Institut für Angewandte Photophysik, Dresden Germany
Microcavities are widely used systems for studying the non-linear interactions of light and matter. Recently polariton lasing  and photon condensation  were demonstrated at room temperature in organic microcavities. Such observations are made possible by the large oscillator strengths and exciton binding energies provided by organic semiconductors. In our work, we fabricate a high quality organic microcavity (OMC), where an active λ/2 layer of the organic host:guest system Alq(3):DCM (2 wt.%) is embedded between two dielectric mirrors (DBRs). The resonance wavelength of this structure is chosen slightly detuned from the peak of the wide emission spectrum of DCM. Between the active layer and the bottom DBR, we incorporate a 40 nm silver layer. This structure is then excited off-resonantly, with a tightly focused laser beam. Via far-field emission spectroscopy, we demonstrate the formation of hybrid Tamm plasmon-polariton states in the OMC. We are further able to pattern the metal layer using a lift-off process to create elliptical defects or photo-lithography to fabricate gratings. As a consequence, the resonances discretise due to optical confinement. In the case of the grating, linear dispersion branches of are observed near the bottom of the cavity mode by angle-resolved photoluminescence. The above, discrete Tamm states are observed to couple to the cavity resonance to form a macroscopically coherent state: Above an optical excitation threshold, we experimentally observe coherent emission at room temperature, comparable to those observed by Lai et al.  We estimate a coherence length spanning at least four periods of the grating. This is larger than the quasimode radius in a comparable unpatterned microcavity. Using numerical simulations, we are able to reproduce the experimental data for the E(k) dispersion of the cavity emission. This procedure provides fundamental insights into the physical mechanisms of phase coupling between cavity and Tamm polaritons. Thereby, we demonstrate how an absorptive metal pattern is employed for mode engineering in an organic microcavity at room temperature.  Kena-Cohen, S. and Forrest, S.R.; Room-temperature polariton lasing in an organic single-crystal microcavity. Nature Photonics, 4, 371-375 (2010).  Klaers, J., Schmitt, J., Vewinger, F. and Weitz, M.; Bose-Einstein condensation of photons in an optical microcavity. Nature, 468, 545-548, (2010).  Lai, C.W. et al.; Coherent zero-state and p-state in an exciton-polariton condensate array. Nature 450, 529-U8, (2007).
K7/CC9: Joint Session
Wednesday PM, November 30, 2011
Room 207 (Hynes)
2:30 PM - K7.1/CC9.1
The Use of Gold Clusters to Enhance Nonlinear Optical Absorption.
Paul Day 1 2 , Kiet Nguyen 1 3 , Ruth Pachter 1 Show Abstract
1 Materials & Manufacturing Directorate, Air Force Research Lab, Wright-Patterson AFB, Ohio, United States, 2 , General Dynamics Information Technology, Inc., Dayton, Ohio, United States, 3 , UES, Inc., Dayton, Ohio, United States
Gold clusters have been studied for their potential as nonlinear optical materials, and indications are that they can compete successfully as two-photon absorbing (TPA) materials with organic compounds. In particular, a TPA cross-section of over 400000 GM has been measured for the thiolated gold cluster Au25(SR)18-1. Another possibility involves combining gold clusters with organic TPA chromophores to obtain TPA materials for specific requirements. In this work, time-dependent density functional theory (TDDFT) has been used to calculate the linear absorption and TPA spectra for a compound where the Au25(SR)18-1 cluster has been coordinated to the donor amino group in the “donor-π-acceptor” compound dimethylamino nitrostilbene (DANS). Challenges for modeling the hybrid material are in finding a level of theory that can successfully model both parts of the system, for example in using an exchange-correlation functional that is also accurate in the asympototic regions, shown to be necessary in modeling chromophores with significant charge transfer such as DANS, and in including relativistic effects, imperative for gold compounds. Other proposed gold clusters and conjugated organic chromophores have been combined in various ways, as will be discussed. The calculated results can aid in the design of new TPA materials.
2:45 PM - K7.2/CC9.2
Plasmonic Nanotubes Analogous to Graphene: Dynamic Control of Three-Dimensional Plasmonic Swiss Rolls.
Jeremy Baumberg 1 , Fumin Huang 1 , Jatin Sinha 2 , Nick Gibbons 1 , Phil Bartlett 2 Show Abstract
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 Department of Chemistry, University of Southampton, Southampton United Kingdom
Three dimensional plasmonic nanostructures and metamaterials exhibit unusual optical properties such as negative refraction, superlensing, and optical cloaking. While recent approaches for fabricating 3D plasmonic nanostructures include electron beam lithography, laser writing, or atomic layer deposition, all of these are compromised in terms of sub-wavelength feature size, scalability of manufacture and cost. Here we report a new class of 3D metamaterials which are the photonic analogue of graphene rolled up into nanotubes.Plasmonic swiss-rolls are fabricated through strain-induced self-rolling from two-dimensional metallic nanopore films. Rolls with lengths up to a several millimetres and core diameters of a few microns are produced displaying strong and striking colours. Their optical properties are readily tuneable across a broad spectral range by simply varying the hole size and thickness of the base nanopore films (an approach not available for the atomic-lattice of graphene). More interestingly they can be dynamically driven by light irradiation, rolling or unrolling with increasing or decreasing light intensity, providing a first demonstration of active tuning of 3D plasmonic nanostructures in the optical frequency range. Such 3D plasmonic metamaterials based on rolling up planar plasmonic structures offer a new general route to 3D construction, and deliver a new set of tuneable plasmonic modes from the quantization around the cylinder axis. The orientation of the roll-up vectors define the symmetry and properties of the plasmonic swiss rolls in an analagous fashion to the chiral indices of carbon nanotubes.The extra degree of freedom in modifying the base properties of the planar films provides a host of new functionalities for these meta-structurs. Various potential interesting applications are opened up, including nano-actuators, nano-motors, and nano-generators.References: Scalable Cylindrical Metallodielectric Metamaterials, N. Gibbons, J.J. Baumberg, et al., Advanced Materials 21, 3933 (2009). Fu Min Huang et al, submitted to Nature Nanotechnology (2011).
3:00 PM - K7.3/CC9.3
Experimental Determination of the Confinement of a Plasmonic Nanocavity.
Kasey Russell 1 , Kitty Yeung 1 , Evelyn Hu 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Optical cavities can tightly confine electromagnetic energy and couple it to optically-active material. Although in the visible and near-IR part of the spectrum this has conventionally been done in dielectric material systems, progress has recently been made in fabricating all-metal optical cavities with coupled emitters. These cavities are designed to have sufficiently small mode volume to enable cavity electrodynamical effects despite their metal-loss limited cavity quality. At such extreme levels of confinement, however, imperfections such as nm-scale roughness of the metal surfaces can lead to significant deviations from ideal behavior, making it imperative to have a method to experimentally measure the degree of optical confinement.Here we present direct measurements of the confinement of a metal-based optical cavity. Our method is based on the observation that the high field confinement of the cavity makes the cavity resonances sensitive probes of the local environment surrounding the cavity. By coating the cavity in a conformal dielectric layer of known thickness and dielectric constant, the frequency of the cavity resonances are shifted. The magnitude of this shift and the thickness of dielectric coating at which the shift saturates provide quantitative measurements of both the mode volume of the cavity (~10-5 μm3) and the exponential decay length of the evanescent fields escaping from the cavity (~10 nm). These measurements are in excellent agreement with finite-difference time-domain simulations.
3:15 PM - K7.4/CC9.4
Angularly Independent Structural Color of Nanostructured Metal Surfaces.
Sylvanus Lee 1 2 , Alyssa Pasquale 2 , Gary Walsh 2 , Marco Romagnoli 3 , Luca Dal Negro 2 Show Abstract
1 Mechanical Engineering, Boston University, Boston, Massachusetts, United States, 2 Electrical and Computer Engineering & Photonics Center, Boston University, Boston, Massachusetts, United States, 3 , MIT/Photonic Corp, Culver City, California, United States
The color of metal surfaces is defined by the absorption and reflection properties of the materials. Although the color of metal surfaces can be drastically modified by engineering resonant phenomena in periodic nanostructures, the incorporation of aperiodic elements is needed in order to demonstrate angularly-insensitive structural colors. Unlike periodic grating arrays, it has been shown that two-dimensional (2D) deterministic aperiodic nanostructures feature broadband frequency responses with wide angular intensity distributions. In particular, the proposed plasmonic Pinwheel and hyper-uniform patterns featuring full rotational invariance in Fourier space are statistically homogeneous and isotropic structures. Therefore, designing nanostructures based on these aperiodic, though deterministic, patterns is ideally suited as a robust approach to generate structural color of artificial metal surfaces. We first experimentally measure dark-field scattering and reflection spectra of periodic and Pinwheel arrays using dark-field scattering spectroscopy and angle-resolved reflection spectroscopy under white light illumination. By measuring the peak wavelength of the dark-field scattering spectra in response to increasing objective magnification, which corresponds to an increase in the angle of light collection, we see that the scattering peaks of the pinwheel gold nanostructured metal surfaces are largely independent on the observation angle and feature a scattering peak at approximately 500 nm. Reflection spectra taken at angles spanning from 30 to 60 degrees demonstrate that periodic arrays red-shift with an increase in detection angle, while the Pinwheel patterns are insensitive to changes in the detection angle. Three-dimensional finite-difference time-domain (3D FDTD) simulations were performed to model the far-field scattering properties of single particles, periodic arrays and aperiodic Pinwheels on gold films. We calculate that gold nanoparticles can support far-field scattering in the green (500-550 nm) when they are on gold films. Simulations of periodic arrays and Pinwheel arrays with N=337 particles demonstrate that pinwheel arrays support isotropic far-field scattering properties, as well as resonances around 550 nm. Our results demonstrate for the first time that, without the incorporation of extrinsic materials and pigments, angularly independent structural color can be observed and detected in nanostructured metal surfaces by dark-field scattering spectroscopy and angle-resolved reflection spectroscopy in deterministic aperiodic Pinwheel arrays under white light illumination. Such nanostructured metal surfaces can be produced in large scale by nano-imprint technology. Hence the coloration mechanism and the insensitivity of observation angle of the proposed device can potentially advance plasmon enhanced optical filters, displays, decorative, sensing and security applications.
4:00 PM - K7.5/CC9.5
High Reflectivity of Nanoporous GaN Distributed Bragg Reflector Made by Doping Dependent Electrochemical Etching.
Sang-Wan Ryu 1 , Joonmo Park 1 2 , Yoon-Han Lee 1 , Sang-Mook Kim 2 , Seung-Jae Lee 2 , Jong Hyeob Baek 2 Show Abstract
1 Department of Physics, Chonnam National University, Gwangju Korea (the Republic of), 2 , Korea Photonics Technology Institute, Gwangju Korea (the Republic of)
A distributed Bragg reflector (DBR) is an essential structure for resonant-cavity light-emitting diodes and vertical-cavity surface emitting lasers. For nitride materials, it is very difficult to fabricate epitaxial DBR so novel structures such as air-gap DBR was investigated. In this work, we fabricated nanoporous GaN DBR using doping selective electrochemical etching. Ten pairs of n-GaN/undoped-GaN were grown first, then periodic circular patterns (diameter= 20 μm, separation= 40 μm) were formed by reactive ion etching. The nanoporous etching was conducted from the etched sidewall at controlled voltage. Only n-GaN was converted into nanoporous layer because of the selectivity of the etching. The nanoporous DBR showed better structural stability than the completely etched air-gap DBR. Reflection spectra were measured and compared with simulation.The fabricated nanoporous DBR was characterized by reflectance spectrum measurement. For the sample etched at 17.5 V, clear stopband was observed and the maximum reflectivity of DBR region was about 85%. The reflection spectrum matched well with the simulation and the refractive index of nanoporous GaN was estimated to be 1.8.
4:15 PM - K7.6/CC9.6
Loss Optimization in Dielectric/Metal Coated Flexible Terahertz Waveguides.
Pallavi Doradla 1 , Cecil Joseph 1 , Jayant Kumar 1 , Robert Giles 1 Show Abstract
1 Physics and Applied Physics, University Of Massachusetts Lowell, Lowell, Massachusetts, United States
The Terahertz (THz) frequency range, located midway between the microwave and infrared region, is a rapidly developing area for source and detection technologies that has shown a promise in biomedical imaging, remote sensing and security screening. For many applications like invivo medical imaging it is necessary to transport and guide THz radiation with minimal transmission loss. A flexible THz waveguide is an essential tool for these applications.Low loss, hollow, flexible waveguides have been designed and fabricated for the maximal transmission of Terahertz (THz) radiation. Polycarbonate (PC) was chosen to be the base material due to its lowest surface roughness. THz radiation can be guided by coating the inner surface of PC tubing with a high reflective metal like Silver (Ag) or Gold (Au). Attenuation characteristics of Terahertz radiation in Ag and Au coated waveguides with bore diameters 4.1mm, 3.2mm, 2 mm were studied at 215μm wavelength. Minimal Propagation loss of 2dB/m was obtained by coupling the lowest loss TE11 mode from an optically pumped terahertz laser into Ag coated waveguide. Transmission loss can be reduced substantially by creating corrugation in metal coated waveguides and by coupling linearly polarized Hybrid mode into it. Corrugation can be achieved in waveguides by the addition of a dielectric layer to the metal coating. Polystyrene (PS) was chosen to be the dielectric, due to its lowest extinction coefficient, which enhances the transmission through the waveguide. By coupling HE11 mode into PS/Ag coated waveguides a minimal propagation loss of less than 1dB/m was achieved. The results will be presented during MRS meeting.