We will discuss a new way to efficiently trap, enhance and manipulate light in nanoscale structures and metamaterials, which is fundamentally different from the traditional way of designing that treats plasmonic components as nanoscale analogs of RF antennas and waveguides. The new approach draws inspiration from hydrodynamics, which studies how the flow of fluids can be manipulated by obstacles strategically positioned in the flow path, and offers a new way to route and re-circulate optical energy within plasmonic nanostructures. New insights into light nanofocusing mechanisms have been obtained by invoking a hydrodynamic analogy of the ‘photon fluid,&’ whose kinetic energy can be locally increased via convective acceleration and then converted into pressure energy to generate localized areas of high field intensity. In particular, we will show how optical energy flow can be molded into optical vortices - tornado-like areas of circular motion of energy flux - which are 'pinned' to plasmonic nanostructures and connected into transmission-like nanogear sequences. Just as mechanical gears and hydrodynamic turbines form the basis of complex machinery, vortex nanogear transmissions can be combined into complex reconfigurable networks to enable nanoscale light routing and switching. We will demonstrate plasmonic nanopatterned platforms engineered in the frame of the new approach and will discuss applications of the new design framework to thermo- and photovoltaics as well as nanoscale heat management. 1. Boriskina, S. V.; Reinhard, B. M. Molding the flow of light on the nanoscale: from vortex nanogears to phase-operated plasmonic machinery. Nanoscale 2012, 4(1), 76-90. 2. Boriskina, S. V.; Reinhard, B. M. Adaptive on-chip control of nano-optical fields with optoplasmonic vortex nanogates. Opt. Express 2011, 19(22), 22305-22315. 3. W. Ahn, S.V. Boriskina, Y. Hong, B.M. Reinhard, “Electromagnetic field enhancement and spectrum shaping through plasmonically integrated optical vortices,” Nano Lett. 2012, 12(1), 219-227.

Plasmonic nanoantennas offer many potential applications in areas as diverse as optical and quantum communications, nonlinear optics, sensing, and photovoltaics [1]. Arrayed nanoantennas like nanoscale Yagi-Uda architectures are particularly suited for these applications because they simultaneously offer high directivity and strong emission enhancement [2,3]. However, while conventional Yagi-Uda nanoantennas are intrinsically narrowband, the recently suggested tapered Yagi-Uda nanoantenna has been predicted to offer strong directionality of emission over a broad spectral range [4]. Such directional broadband nanoantennas may find important applications in high-bandwidth wireless on-chip communication and spectroscopy, multichannel sensing, and light harvesting devices [3]. Here, we experimentally demonstrate the performance of the tapered Yagi-Uda optical nanoantennas consisting of 21 equally spaced nanorods: a reflector, a principal feed element, and an array of gradually tapered directors. We confirm that such novel nanoantennas can operate over a large spectral bandwidth in the telecommunication optical range. For fabrication we have employed electron-beam lithography followed by evaporation of 50 nm of gold and a lift-off procedure. In order to allow for assessment of the optical sample quality by means of far-field spectroscopy, we have arranged a large number of nominally identical antennas in a two-dimensional array. The taper angle has been chosen to be 6.6 degrees for optimal nanoantenna performance [5]. As a reference structure, we have also fabricated nanoantennas without the tapers. We have collected normal-incidence linear-optical transmittance spectra of these two types of nanoantennas using a white-light spectroscopy setup and an optical spectrum analyzer. For the tapered nanoantennas, the measured transmittance spectra reveal a fundamentally different behaviour as compared to their untapered counterparts. Importantly, their resonances show a characteristic double-dip line shape. This line shape originates from an overlap of the resonances of the individual nanorods, and, in combination with the large FWHM of the collective response exceeding 600 nm, directly reflects the nanoantennas&’ broadband characteristics. Our results are in a good agreement with the full-vectorial numerical calculations, further demonstrating the origin of the observed spectral features. [1] P. Biagioni et al., “Nanoantennas for visible and infrared radiation,” Rep. Prog. Phys. 75, 024402 (2012). [2] A. G. Curto et al., “Unidirectional emission of a quantum dot coupled to a nanoantenna,” Science 329, 930 (2010). [3] I. S. Maksymov et al., “Optical Yagi-Uda nanoantennas,” Nanophotonics, in press (2012). [4] I. S. Maksymov et al., “Enhanced emission and light control with tapered plasmonic nanoantennas,” Appl. Phys. Lett. 99, 083304 (2011). [5] I. S. Maksymov et al., “Multifrequency tapered plasmonic nanoantennas,” Opt. Commun. 285, 821 (2012).

In this study we have investigated the performance of a meta-surface consisting of concentric plasmonic multi-material loops. The unit cell of the periodic array is plasmonic loops with dielectric in between. Finite difference time domain technique is used to obtain the performance of this complicated meta-surface. Based on the number of the plasmonic layers, given that they are engineered properly, we have shown that this meta-surface can have multi-resonances. Furthermore, each resonance, which is a null in transmission spectrum, can be fully controlled by changing the parameters of the resonating layer. Generally the aspect ratio of the loop thickness and diameter is dictating the resonant frequency. As an example we have shown that by increasing the resonating layer thickness while the outer diameter of the loop is fixed, the resonance would occur at a higher frequency. Based on the material used as the plasmonic loops, we can have the resonance in different spectrums, given that the size of the loop is in sub-wavelength limit. To have the resonance in the visible spectrum Silver or Gold can be used while ITO loops resonate in mid-infrared band. The dielectric loop in between the two concentric loops is another tool for fine-tuning the resonances. The Fano shape resonance is clearly shown when the plasmonic loops are close enough in a way that the near fields of the two adjacent resonators are interfering constructively and destructively to make the bright and dark modes, respectively. Compared to other structures that have Fano like resonance, like the concentric loop/disk design, the proposed structure has more flexibility in tuning the frequency of the super and sub-radiant modes. The multi resonance behavior is another advantage of the proposed design compared to other Fano resonators.

We report a new technique to measure the mid-infrared photothermal response of plasmonic metamaterials that are engineered for functional studies on monolayers of proteins and other biomolecules. Heterodyne measurement is implemented to detect the thermally induced modulation of a Ti:sapphire probe laser by lock-in detection. Informed by numerical simulations, electron beam lithography is used to fabricate nanostructures that enhance selected vibrational infrared “fingerprint” modes of biomolecules. To demonstrate the photothermal heterodyne technique we use 4-cyano-4&’-pentylbiphenyl (5CB) liquid crystal, which has a large index of refraction change in the nematic phase. Tunable infrared Quantum Cascade Laser (QCL) has a spectral brightness more than 105 greater than the FTIR Globar blackbody source and >102 greater than mid-infrared synchrotron radiation. It promises to provide unprecedented sensitivity when combined with engineered plasmonic metamaterials. A home-built photothermal setup is used in combination with a tunable QCL, a plasmonic substrate, an inexpensive silicon photodetector and lock-in detection to measure the sensitivity and specificity of performing vibrational infrared spectroscopy on biomolecules. The photothermal mid-infrared response has the potential to detect ultralow concentration of absorbers using low-cost photodetectors and bright tunable QCLs.

In my group, we have been exploring the modularization and parameterization of metamaterials in order to endow metamaterials with new functionalities and characteristics. We are investigating how metamaterials, when properly designed as collections of material segments (e.g., metamaterial “bits” or “meta-bits”), can become “metasystems” that may provide us with interesting platforms for computation and information handling. From such paradigms, we may obtain “meta-functions” that can be due to proper combinations of meta-bits, meta-systems, and metastructures. We explore how such “meta-machines” and “meta-bits” can provide potentials for ease of design, and manipulation of mathematical functions and equation solving, providing us with new directions of metamaterials as discrete compact information processors. In this talk, I will present some of the concepts, features, and directions in the functionalization of metamaterials and “meta-machines” that are being studied in my group.

The optical properties tunability of plasmonic nanomaterials as a function of size and shape and the ability to localize electromagnetic fields in specific locations makes these materials promising for applications raging from sensing and biomedicine to imaging. While the nanoscale features of these materials determine their optical properties, these are typically assessed as an average at the macroscale. Consequently, theoretical calculations of idealized structures are typically used to visualize the electric field distribution in the near field. In this work the electric field enhancement of gold Asymmetric Spilt Ring Resonators (ASSR) was determined experimentally with 100 nm lateral resolution using the Photothermal Induced Resonance (PTIR) technique. PTIR, is a new technique that combines the chemical sensitivity of IR spectroscopy to the lateral resolution of Atomic Force Microscopy (AFM). PTIR uses a tunable pulsed laser for sample illumination in ATR configuration and an AFM tip in contact mode to measure the sample instantaneous thermal expansion induced by light absorption. PTIR spectra are obtained by plotting the amplitude of the tip deflection, which is proportional to the energy absorbed, with respect to the laser wavelenght. Electron Beam Lithography was used to fabricate gold ASSR, with diameters ranging from 700 nm to 2000 nm, directly on ZnSe prisms. The ASSR plamonic resonances were tuned from 2900 cm-1 (3.49 µm) to 850 cm-1 (11.77 µm) as a function of size. The PMMA coated ASSR were characterized macroscopically with a FTIR spectroscopy and at the nanoscale with the PTIR technique. PTIR images are acquired simultaneously with AFM height images by illuminating the sample at a fixed wavelength. The PTIR images recorded in correspondence of the PMMA molecular absorptions allows a direct visualization of the electric field enhancement with a lateral resolution of approximately 100 nm. PTIR images clearly show the position of hot spots as a function of exciting wavelength and allow visualizing the interaction between nearby nanostructures as a function of distance. The experimentally determined enhancement factors (100 nm resolution) vary from 2 to 200 as a function of position. We believe that our work will foster the optimization and engineering of plasmonic materials towards their technological applications.

Nanowire metamaterials are a class of materials formed by an array of aligned plasmonic nanowires embedded in a dielectric host which exhibit strongly anisotropic behavior. For a wide range of excitation frequencies, the optical properties of these systems are dominated by two waves with different polarizations. In contrast to this behavior, in the epsilon-near-zero (ENZ) frequency range, excitation of an additional wave mode has been observed in experiments. In this frequency range the contribution of spatial dispersion becomes increasingly important and a modified dispersion relationship for the anisotropic metamaterials must be used. The properties of the additional wave need to be taken into consideration during design and analysis of the properties of nanowire-based systems . Here we present analytical and computational studies of the nonlocal optical response of plasmonic nanowire metamaterials. Dispersion of photonic modes of plasmonic metamaterials have been studied using finite-element-method (FEM) simulations and 2D rigorous coupled wave analysis (RCWA) as a function of wavelength, geometry, and material parameters. The additional transverse magnetic (TM) wave has been observed in the ENZ regime using both techniques. Analytical description of the optical properties of nonlocal nanowire systems has been developed. It is shown that optical response of the system results from the coupling of conventional effective-medium-dominated oscillations of polarization in the plane perpendicular to the nanowires with plasmon-polariton-type oscillations of the polarization in the direction of nanowires. The presented model is in agreement with numerical solutions of Maxwell&’s equations.

Spontaneous emission of a dipole can be strongly modified in nanostructured systems and metamaterials due to drastic changes in radiative and non-radiative transition probabilities as well as modification of propagating modes. Significant changes in kinetics, yield, spectra and angular distribution of Eu3+ luminescence were demonstrated in Eu3+ organic films deposited on nanostructured plasmonic surfaces and multilayers in comparison with similar films placed on dielectric and metal flat substrates. In particular, a relative decrease in p-polarized light was found for electric dipole transitions of Eu3+ in opposite to what was observed in flat systems and expected from the image dipole consideration. Modification of the magnetic dipole emission at ~590 nm was found to be different than that of electric dipole-related transitions, due to different coupling of magnetic dipoles with plasmonic excitations. Spectrally-resolved near field studies confirmed the character of the effects and provided an additional insight. The results are discussed in terms of equivalent circuit consideration with taking into account coupling of dipoles, plasmonic and propagating modes.

Metamaterials, plasmonics and optical antennas have recently evolved as new research areas attracting widespread attention. Bridging the three disciplines, we theoretically conceive and experimentally demonstrate a novel magnetic antenna that can generate unidirectional surface plasmon polaritons (SPPs) very efficiently. This novel device consists of two subwavelength magnetic resonators with detuned resonant frequencies. At the magnetic resonance frequency, an incident optical wave can be efficiently channeled into SPP mode. By tailoring the relative resonance phase and the separation between two resonators, we can steer SPPs to propagate predominantly along one direction owing to the constructive and destructive interference of SPPs. The dimension of the device is smaller than the wavelength in all three dimensions. Furthermore, due to the strong magnetic resonance nature, the normalized generation efficiency of SPPs is as high as 125%, which is at least three times larger than the single slit case and six times larger than the single aperture case. We employ leakage radiation microscopy and conoscopic microscopy on single antennas to experimentally demonstrate the unidirectional excitation of SPPs at the air-gold interface. The experimental results are in good agreement with the full-wave finite element simulation and magnetic dipole approximation. Similar to conventional optical antennas in regards to free-space propagating waves, our magnetic antennas pave a new way to manipulate near field optical waves, which can be used as an efficient nanoscale plasmonic directional antenna. Such antennas may also be useful for nonlinear applications, active modulation and wireless optical interconnects based on surface plasmons.

Phononic metamaterials are artificially structured materials (at certain length scales) that provide promise in controlling the propagation of phonons in solids. However, the vector nature of the phonon makes the development of a governing framework with which to guide the design of these phononic metamaterials complicated and no coherent framework currently exists for the design of phononic structures. While most designs (to date) focus on the “meta-atom” (building block) approach, the spatial arrangement i.e. plane/space group (non-locality) is equally instrumental in dispersion engineering, in far-reaching ways. In this work, we utilize a combination of global symmetry principles, adopted from group theory, as well as “local” symmetry principles, adopted from conservation principles and directed by group theory, to formulate our generalized design framework. In particular, we demonstrate how the Wyckoff decoration of the meta-atoms and the mechanical topology of the overall structure determine the intricate details of the dispersion relation. This leads to the result that the global trajectory and topology of the dispersion bands in k-space may be dictated by the “local” design of the unit cell; it further provides a rational explanation of the role of volume fraction in the detailed dispersion relations of the metamaterial. By utilizing a single material platform throughout and with the same unit cell dimensional constraints, the design of phononic metamaterials possessing i) multiple complete in-plane spectral gaps totaling over 100% in normalized gap size; ii) a single complete in-plane spectral gap of 102% and a complete spectral gap of 88%, as well as iii) an in-plane sub-wavelength gap of 85% are demonstrated. This demonstrates the ability of the framework to mold dispersion across meso-scopic frequencies simply through geometric design. Finally, we discuss how a judicious choice of mechanical topology and Wyckoff site selection may be utilized to rationally design bands with tailored group velocity, even in the deep sub-wavelength regime (below 0.2 of the Bragg gap frequency), opening up possibilities for controlling broadband wave propagation behavior, such as negative refraction. This relaxes the need for multiple materials to create sub-wavelength metamaterials, as well as generalizes the process of designing dispersion relations and unique propagation behavior at sub-wavelength scales. This two-scale global and local approach provides new avenues for designing PM, especially with utilizing a single material platform, allowing for the extension and realization of new devices without the intrinsic reliance on different material parameters.

Evanescent wave that carries object&’s fine features decays rapidly in the near field. The loss of evanescent wave components in the imaging region is the fundamental reason of the diffraction limit of the conventional imaging system. It has been demonstrated that acoustic metamaterials with anisotropic dynamic mass are able to capture and transmit evanescent waves by preserving or enhancing their wave amplitudes, by use of anomalous dispersion and resonant transmission mechanisms. We propose a metamaterial slab lens, which is made of an array of aluminum tubes with subwavelength channels of periodically varied cross sections. Such a structured slab lens is characterized by anisotropic dynamic mass, and effective mass in the direction parallel to the lens interface is infinity due to the large impedance mismatch between the aluminum and background air. Such anisotropic effect produces the anomalous dispersion, by which propagating wave vectors are weakly dependent on the spatial frequency of evanescent waves. As a result, all evanescent waves are coupled to the subwavelength channels and propagate with the same wavenumber. Analytic solutions of evanescent waves transmitting through the structured channels are constructed, and the resonant tunneling condition that results in complete transmission of evanescent waves is derived. It is found that the resonant tunneling arises from strong oscillation of Bloch waves in the periodically corrugated channels. Such a mechanism allows the tunneling frequency tuned by geometric parameters of structured channels. Finally, the metamaterial slab lens is fabricated. The imaging experiment demonstrates that the proposed lens can clearly distinguish two sources separated in the distance below the diffraction limit at the tunneling frequencies. The research may have potential applications in achieving high resolution in medical imaging.

In the past few decades, the concepts of fractal geometry have been introduced into electromagnetic and plasmonic metamaterials. With their self-similarity different length scale, structures based on fractal geometry could achieve multi-band character or broadband structure. However, there exist few studies of phononic metamaterials based on fractal geometry. We simulate the properties of the phononic metamaterials based on fractal geometries to investigate the wave propagation in two-dimensional systems use COMSOL multiphysics package. The numerical study of these systems, guided by our recently developed general design framework, help to understand the role of geometric factor in determining the phononic properties of the structures. Given the deterministic nature of the structures studied, the proposed fractal structures can be fabricated via standard lithographic or 3D printing techniques. The wave behavior of the structures can be characterized using Brillouin Light Scattering, Scanning Acoustic Microscope and Near-field Scanning Optical Microscopy. With their unique dimensional property, compared to conventional structure, they have the potential to enable compact structures/platform, hence reduced footprint that would be beneficial for miniaturization of advanced devices.

Development of ideas in classical wave propagation has generally followed the trend whereby new concepts such as photonic crystals and metamaterials initially appearing in optics / electromagnetism subsequently get extended to acoustic waves. On the other hand, phenomena such as negative refraction and negative group velocity have been known in acoustics well before the advent of metamaterials. For example, negative curvature of acoustic slowness surface encountered in anisotropic media permits negative refraction at an interface and “backward reflection” at a free surface. The fact that a straight interface between two anisotropic media can serve as a lens was noted by Mason as early as in 1973 [1]. More recently, the Veselago lens effect was observed with Lamb modes in an elastically isotropic plate with a thickness step [2]. In this case, negative refraction is made possible by the existence of “backward propagating” waveguide modes, a phenomenon well known in acoustics [3] that has also been predicted to exist in optics [4]. Negative refraction occurs whenever a backward propagating mode is converted into a forward propagating mode at an interface. In this presentation, we provide an overview of negative refraction without metamaterials, describe recent results demonstrating this phenomenon in two-dimensional elastic waveguides and discuss the possibility of its occurrence in optical slab waveguides. [1] I. M. Mason, J. Acoust. Soc. Am. 53, 1123 (1973). [2] S. Bramhavar, C. Prada, A.A. Maznev, A.G. Every, T.B. Norris, and T.W. Murray, Phys. Rev. B 83, 014106 (2011). [3] A. Viktorov, Rayleigh and Lamb Waves (Plenum, New York, 1967). [4] M. Ibanescu, S.G. Johnson, D. Roundy, C. Luo, Y. Fink, and J.D. Joannopoulos, Phys. Rev. Lett. 92, 063903 (2004).

In this talk I will show how the use of time dependent and broadband wavefields, in conjunction with metamaterials, permits to beat the diffraction limit from the far field for imaging or focusing purposes. I will introduce the idea of resonant metalens, first demonstrated in the microwave domain, and explain its principles. In particular, I will show how the concept of time reversal can be utilized to focus in this metamaterial based lens and from the far field, onto focal spots much smaller than the diffraction limit. I will then prove the generality of the approach by demonstrating its transposition to the acoustic domain thanks to a very simple setup: an array of soda cans. Then I will present our latest theoretical and numerical results obtained using a resonant metalens made out of plasmonic nanorods in the visible part of the spectrum. I will show that this lens allows, using polychromatic light, to focus light using far field time reversal onto spots as small as 1/30 th of the wavelength in the visible. Finally I will prove that our approach can also be used in order to image from the far field and with a subwavelength resolution and could lead to real time sub-diffraction imaging systems.

Recent advances in manufacturing using microlattice structures [1] have enabled the realization of ultra-light yet ultra-stiff elastic materials not found in nature. Due to their high elastic moduli, these materials have the potential to be used as components in coordinate transformation-based guided wave applications where large sound speeds are required. We present evidence that sonic crystals composed of air-filled elastic shells result in an acoustic analogue of these hollow microlattice materials [2]. Each air-filled elastic shell behaves as an effective fluid scatterer at wavelengths longer than the shell&’s diameter, with a high effective fluid bulk modulus but low effective fluid density compared to dense liquids such as water. When combined into a regular lattice, the material composition, thickness and diameter of the constituent elastic shells can be tuned to attain a wide range of effective material properties. We also demonstrate that for a specific shell thickness each individual elastic shell becomes impedance matched to the background fluid, which in turn guarantees acoustic transparency when these shells are combined into a lattice. We emphasize that the scattering properties of the shells are based on a homogenized effective medium description and therefore the transparency will be a broadband phenomenon in the homogenization limit. We present examples of metamaterial applications using transparent sonic crystal lattices. Work supported by the Office of Naval Research. [1] T. A. Schaedler, A. J. Jacobsen, A. Torrents, A. E. Sorensen, J. Lian, J. R. Greer, L. Valdevit, and W. B. Carter, Science 334, 962 (2011). [2] T. P. Martin, C. N. Layman, K. M. Moore, and G. J. Orris, Phys. Rev. B 85, 161103(R) (2012).

Recent advances of silicon devices along with high integration and miniaturization demand precise evaluation and control of atomic vacancy on silicon wafers surface. The surface-acoustic wave (SAW) is a promising candidate for detecting such atomic-level defects. However, the visualization technology of a SAW on crystalline surface is developed only recently.[1] On the other hand, negative refraction and a lens effect of acoustic wave in two dimensional isotropic media like phononic crystal[2] has been attracting much attention as a new route for artificial control of acoustic wave. If these effects are realized on semiconductor crystal surfaces, the aforementioned application, a non-destructive detection of the atomic-level defects, can become possible. Using a large-scale molecular dynamics simulation, the present study explores behavior of SAW in Si surface, the influence of anisotropy of a crystal, an interaction of the wave with a surface defect, and possibility to realize a filter or a lens effect by an artificial nanostructure formed on the surface. We employ a molecular dynamics simulation for investigating the acoustic-wave propagation on Si surface of 5.3-nm-thick slab. The Stillinger-Weber potential[3] was adopted for interatomic potential of the Si system. For efficient calculation of a large-scale system, the parallel computing technique based on the domain-decomposition method was used with the standard MPI library for internode communications. A nanostructure consisting of a periodic array of holes was adopted for modulating the SAW on Si slab. We estimated hole size and lattice spacing so that the band gap frequency by Bragg reflection in the periodic structure is near 3THz. (Radius of the hole is 0.58 nm and the lattice spacing is 1.6 nm.) We also calculated phonon density of state by the molecular dynamics method for estimating phonon dispersion in the structure. It is shown that band gap frequency was controllable via changing the interval between holes, i.e., the hole density. Moreover, the gap width tends to be wider as the density of a periodic array of holes be higher. Based on these analyses, we designed the waveguide structure surrounded by a periodic array of holes. When a lattice vibration with frequency of 1THz is induced at the center of the waveguide, an acoustic wave propagates into the periodic structure. On the other hand, when the induced wave is at 3THz, an acoustic wave is confined and propagates only within the waveguide, as accordingly designed. The details of the design strategies and attempts toward a realization of lens effect by the nanostructure will also be discussed in the presentation. References : [1] Y. Sugawara et al., Phys. Rev. Lett. 88, 185504(2002). [2] Y. Kasai et al., Jpn. J. Appl. Phys.50. 067301 (2011). [3] F. H.Stillinger and T. A. Weber, Phys.Rev.B.31,8(1985).

We present an experimental demonstration of a reconfigurable acoustic metafluid having anisotropic, actively controllable speed of sound for ultrasonic waves. The acoustic metamaterial is based upon suspensions of subwavelength discoid particles whose orientation and interparticle interactions are manipulated by external magnetic fields. Measured sound speeds are direction- and frequency- dependent, changing in a nonlinear fashion with particle concentration when an external magnetic field is applied. The observed changes in sound speed are significantly greater than that expected for suspensions of oriented but non-interacting oblate-spheroidal particles, suggesting that interactions between particles are important even for particle volume fractions below 0.5%.

We present an experimental realization of a nonlinear phased array to focus highly compact waves in solid media. The phased array consists of parallel chains of spherical particles in contact. When the chains are excited by an impulse, the nonlinear Hertzian force between elastic spheres allows for the formation and propagation of a solitary wave: a localized collective motion of the spheres, which maintains its shape over a long length of travel and carries a significant quantity of mechanical energy. Unlike in linear media, the speed of these solitary waves can be tuned by applying a compressive force to the chain. The different pre-strain applied to the chains induces a signal delay in the system. When the phased array is placed adjacent to a medium of interest, it can focus the transmitted pulses of energy to a chosen location in the medium, creating a “sound bullet”. In our experimental setup, the chains are composed of hardened stainless steel spheres, which are struck using piezo-stacks. This approach allows for timing to be controlled using both pre-compression applied by a system of springs and set-screws or by the timing of the piezo-stacks. The formation and properties of the sound bullets are measured in a bulk solid by use of a laser-dopplometer system. We investigate the ability of this system to change its focal point by changing the applied pre-compression. Experimental results are compared to numerical predictions.

Central to the idea of metamaterials is the concept of dynamic homogenization which seeks to define frequency dependent effective properties for Bloch wave propagation. Recent advances in the theory of dynamic homogenization have established the coupled form of the constitutive relation (Willis constitutive relation). This coupled form of the constitutive relation naturally emerges from ensemble averaging of the dynamic fields and automatically satisfies the dispersion relation in the case of periodic composites. Its importance is also notable due to its invariance under transformational acoustics. Here we discuss the explicit form of the effective dynamic constitutive equations. We elaborate upon the existence and emergence of coupling in the dynamic constitutive relation and further symmetries of the effective tensors. Finally we elaborate upon the dependence of the constitutive relation on the architecture of the unit cell by way of explicit calculations for a full 3-D periodic composite.

Fabrication of Structured Nanocomposite Materials for Three-Dimensional Metamaterial Applications We present a technique that combines top-down and bottom-up nanofabrication approaches to create a structured nanocomposite material. The structured nanocomposite material consists of three-dimensional (3D) silver nanostructures embedded inside a doped polymer matrix. The positioning of silver structures within the matrix is controlled via femtosecond laser irradiation. The key is to use a material combination that yields a stable background dielectric matrix while allowing nanostructure growth inside the laser irradiated volume. We prepare samples that contain Ag+ ions inside a transparent polymer matrix. Femtosecond laser pulses are focused inside the matrix, inducing multiphoton photoreduction reactions. These reactions are localized to the focal volume of the laser and lead to the nucleation and growth of silver nanoparticles. Since the silver growth process is limited to volumes irradiated by the laser pulses, we can precisely control the location of silver nanostructures inside the polymer matrix and create 3D patterns. The nonlinear nature of the absorption process allows us to modify the transparent material in three-dimensions and obtain resolutions higher than the linear diffraction limit of the laser. We show sub-300 nm resolution silver structures. We create, for example, 3D arrays of disconnected silver nanostructures that are not feasible using other techniques. Samples are characterized using scanning electron microscopy, transmission electron microscopy, as well as optical techniques. 3D nanofabrication techniques are increasingly important for nanophotonics and metamaterials. Many applications in these fields also require the precise integration of multiple materials, such as metals with dielectrics. The presented technique is well suited for nanophotonic and metamaterial applications and can produce structures not feasible using other methods. The technique can also be applied to alternative material combinations, including other metals or semiconductors.

Metamaterials are engineered metallic structures to tailor the optical response. One of the most known metamaterials are metal-insulator-metal structures where metallic nanostructure array is separated from a continuous metallic surface with a dielectric layer[1-3]. Such surfaces are used for energy and sensing applications where the wide angle and perfect absorption is possible[4-5]. On the other hand, for energy and spectroscopy applications broadband metamaterials are desired. Multispectral nanostructures are designed recently by coupling of localized surface plasmon and grating coupled surface plasmons modes[6]. Here we report the design, fabrication, characterization and modelling of plasmonic meta-surfaces with broad spectral response. The proposed structures are ultra thin(~160nm) and have subwavelength periods(~250-300nm) and have wide angle spectral response. The structures are fabricated on silicon wafer. The fabrication is started with e-beam evaporation of germanium, silver and aluminum oxide on silicon wafer where the germanium layer acts as adhesion and wetting layer. Then the nanodisc structures are defined using e-ebeam lithography system. The diameter of the discs are simply tuned by the dose of electron beam. Then the final structures are defined with e-beam evaporation of silver and subsequent liftoff. The optical response of final structures are characterized by normal illumination reflectance setup. The measured spectral response of these structures are broad and tuned by changing the diameter of the nanodiscs for TM and TE polarizations. Also, we also mapped the optical response of these metasurfaces with a computer controlled focused illumination setup with different objectives(20x, 50x,100x) with submicrometer resolution. The obtained multispectral and broad spectral characteristics of these structures are verified with FDTD and FEM simulations. Finally, we extended our understanding of coupling of localized surface plasmon modes by using a simple lumped circuit model.1.N. I. Landy et.al. ,Phys. Rev.Let., 100, 207402 (2008) 2.X. Liu et.al, Phys. Rev. Let. 104, 207403 (2010) 3.J. Hao et.al.,App.Phys. Let., 96, 251104(2010)4. D. Chanda et. al. ,Nature Communications,2,479(2011) 5.Na Liu et. al, Nano Letters,10,7(2010) 6.Y. Chu et. al., ACS nano VOL. 5,NO. 1(2011)

We propose a full description of the behaviour of amplifying waveguides based on an insulating matrix doped with silicon nanoclusters (Si-nc) and rare-earth ions (Nd3+). A pumping electromagnetic field creates excitons in the Si-ncs that, in turn, efficiently excite the rare earth ions to achieve level population inversion necessary for a positive net gain of a typical signal at 1060nm corresponding to a Nd3+ transition. We describe the electromagnetic field using an FDTD algorithm to solve the Maxwell equations coupled to auxiliary differential equations (ADE) that rule the levels populations evolutions. One of the major issues of such a numerical solution lies in the difference between two characteristic times: the electromagnetic field period (~10^-15s) and the levels lifetimes (microseconds). Since, for numerical stability, the time step must be lower than the shortest characteristic time of the system, 10^11 time iterations would be required to describe the population evolution over 1microsecond. To overcome this problem, we propose an iterative algorithm based on the ADE-FDTD method. In a first step, the electromagnetic field is propagated along the structure using constant level populations.A stedy state is reached after which, in a second step, we compute the population evolution with a larger time step. Once the population steady state is reached, we again perform step 1 and step 2 until an overall steady state is reached. In this frame work we present for several waveguiding geometries the spectral gain as a function of pumping mode (co-propogation with signal, top-pumping) and all physical parameters (Si-nc and rare earth ion concentrations, geometry of the waveguide, refractive indices, energy transfer efficiency between Si-nc and rare earth ions).

Molecular spin devices (MSD) are capable of harnessing the controllable transport and magnetic properties of molecular device elements and are highly promising candidates for revolutionizing computer logic and memory. A MSD is typically produced by placing magnetic molecule(s) between the two ferromagnetic electrodes. Recent experimental studies show that the molecules produced unprecedented strong exchange couplings between the two ferromagnets, leading to intriguing magnetic and transport properties in a MSD. Future development of MSDs will critically depend on obtaining an in-depth understanding of the molecule induced exchange coupling and its impact on MSD&’s switchability and temperature stability. However, large size of MSD systems and unsuitable device designs are the two biggest hurdles in theoretical and experimental studies of magnetic attributes produced by molecules in a MSD. This research theoretically studies the MSDs by performing Monte Carlo Simulations (MCS), which have the capability to tackle large systems. Our 1-3D MCS shows that a molecular magnet, with net spin state, can produce transformative effect when producing ferromagnetic exchange coupling with one electrode and antiferromagnetic exchange coupling with the other electrode. 2D-MCS showed that existence of three different regimes with increasing temperature: for the low temperature, two ferromagnetic electrodes aligned in the same direction; for the middle temperature, range molecular magnet forced the magnetization of the two electrodes in the opposite direction leading to a total zero magnetization; for the higher temperature, MSD was thermally unstable. Effect of dimensionality, system size, temperature and magnitude of the exchange coupling strength between molecular magnets and ferromagnetic electrodes was studied. This study not only provides a practical route to define the operational temperature ranges for the futuristic MSDs but also provide crucial guidelines for designing novel MSDs. Molecule couplers between ferromagnetic electrodes are capable of producing novel form of magnetic metamaterials.

Fundamental shortcomings of ferroelectrics are the low induced strain and high electric field required for practical applications in actuation, sensing and acoustics. Although relaxor ferroelectrics deliver significant improvements, fatigue remains a drawback in achieving reliable switching. We have recently demonstrated domain-engineered relaxor ferroics exhibiting low field-induced, reversible and sustainable strain associated with the rhombohedral (FR) - orthorhombic (FO) phase transition in Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT). Poled [011] single crystals with compositions close to the morphotropic phase boundary (MPB) were investigated under stress and electrical bias. The elastic response of PIN-PMN-PT displays a strong and sharp discontinuity associated with a stress induced (FR- FO) phase transition that can be tuned by electric field. For states poised at the FR-FO phase boundary we have obtained bulk strain of ~ 0.5%. (Finkel, et al, Appl Phys Lett 98, 192902 (2011)) at a drive field more than an order of magnitude smaller than that required using the linear (d33~ 2000 pm/V) piezoelectric mode. We also find lack of fatigue after several millions cycles due to strain accommodation that allows for sustainable phase switching. Polarized light microscopy and X-ray diffraction are in very good agreement with macroscopic observations and a phenomenological model confirming the proposed transformational path. We present our results on giant electro-mechanical energy conversion under the FR-FO phase transformation. It is demonstrated that under mechanical pre-stress, a relatively small oscillatory stress drives the material reversibly between FR and FO phases with remarkably high polarization and strain jumps induced at zero bias electric field and room temperature (Dong , et al, Appl Phys Lett 100, 042903 (2012)). The measured electrical output per cycle is more than an order of magnitude larger than that reported for linear piezoelectric materials. Variable multiferroic and magnetoelectric devices based on this phase transition- related giant coupling in relaxors will be discussed.

Materials are central to realisation of new ideas, whether as experiments or as commercial devices. This is especially true when electromagnetic radiation is concerned as the material properties available from nature are somewhat limited. The concept of metamaterials has enormously expanded horizons in this respect, creating for the first time not only materials with negative refractive indices, but a host of other properties that would otherwise be difficult or impossible to find. The concept is a simple one: structuring a material on a scale much less than the wavelength changes its properties, but enables a description in terms of electrical permittivity and magnetic permeability to be retained. A dramatic example is the metal silver which in solid form highly reflecting surfaces, but in colloidal form, as in photographic film, is a black absorbing material. The richness of choice offered by the metamaterial concept is matched by a new design technology referred to as transformation optics. Macroscopic optical devices much larger than the wavelength of light are designed by tracing rays of light using Snell's law. However on the nanoscale at which much of the modern developments in optics take place, rays are no longer a meaningful concept. Instead transformation optics is precise at the level of Maxwell's equations and operates on the magnetic and electric fields lines giving prescriptions for controlling their flow which can then be realised using metamaterials. I shall describe recent developments in the fields and future prospects.

The strong optical field confinement in optical micro-/nano-cavities leads to many fundamental studies and exciting applications in nanophotonics. The sizes of these conventional dielectric cavities cannot be smaller than wavelength scale for efficient photon confinement, which is limited by the low refractive indices of nature materials. We have investigated theoretically indefinite medium with hyperbolic dispersion can be used to miniaturize optical cavities due to the supported unbounded large wave vectors. Here, by incorporating multilayer indefinite metamaterials, we experimentally demonstrate deep-subwavelength optical cavities with sizes down to ~lambda;/12. The metamaterial structure consists of alternating thin layers of silver(Ag) and germanium(Ge). These cavities are highly anisotropic, resulting in a hyperbolic iso-frequency contour(IFC). The hyperbolic dispersion permits the access to wave vectors much larger than that in air and the tremendous momentum mismatch between the metamaterial and the air causes the total internal reflection at the interface. By cutting the metamaterial into a nanoscale cube, 3D optical Fabry-Pérot cavity can be formed with a high effective refractive index equals to k/k_0. Since arbitrary large wave vectors can be reached along the unbound IFC hyperbolic curve, the cavity size can be arbitrarily small. Multilayered metamaterial with 20nm Ag and 30nm Ge is fabricated in experiments Cavities with different sizes are aligned at the identical resonant frequency of 191 THz for the (1, 1, 1) modes, which exemplifies one of the unique features of indefinite cavities. For the same cavity, the (1, 1, 2) mode has a lower frequency compared to the (1, 1, 1) mode, showing the anomalous mode dispersion. Also, the transmission depth is different for each cavity mode, indicating the coupling between the excitation plane wave and the cavity mode strongly depends on the cavity size and the mode order, which is related to the resonating wave vector supported inside the cavity. The retrieved radiation quality factor extracted from the measured transmission spectra, based on the coupled mode theory, shows vertical and total radiation quality factor is proportional to the fourth power of effective index. Also, the indefinite metamaterial cavities allows unnaturally high effective refractive index and a maximum value of 17.4 is demonstrated for the (1, 1, 2) modes. The demonstrated nanoscale metamaterial optical cavities significantly differ from the conventional dielectric cavities, showing anomalous mode dispersion and unique universal fourth power law between the radiation quality factor and the resonating wave vector. This new type of optical cavities will greatly extend the ability to manipulate light at deep-subwavelength scale for potential applications including light-matter interactions. References: "Experimental Realization of 3D Indefinite Cavities at Nanoscale with Anomalous Scaling Law", Nature Photonics (in press)

Control of spontaneous emission properties is crucial for a broad range of applications such as single-photon sources, efficient lasers, displays, solar energy harvesting, and biological markers. Quantum dot (QD) emission can be efficiently controlled by coupling to photonic structures such as microcavities and photonic crystals [1,2]. It was also shown that nanostructured plasmonic materials can be superior for emission enhancement due to their high local-field enhancement and good coupling to free space [3,4]. However, experimental demonstrations of controlling QD emission via coupling to magnetic metamaterials have not been reported so far. Here we couple QD emission to the resonances of magnetic metamaterials. We compare the emission enhancement for the zero-order electric and the first-order magnetic resonances (matched spectrally to the QD emission, with the same strength but orthogonal polarisations). We observe three-fold enhancement of the QD emission into the magnetic mode in comparison to the electric one. The system investigated here is a planar magnetic metamaterial composed of split-ring resonators (SRRs) covered by a 200nm-thick layer of polyvinyl alcohol (PVA) containing core-shell QDs emitting at 790nm. In order to investigate how the QD PL is influenced by coupling to the different modes of the magnetic metamaterial we have performed QD micro-photoluminescence (PL) spectroscopy and micro-PL spatial mapping on the SRR metamaterial. We observe broadening of the QD PL spectrum for the electric resonance, while for the magnetic resonance a narrowing of the QD PL emission spectrum is observed. In addition, while the PL intensity doesn't change when coupling to the electric resonance, a three-fold enhancement is observed in the magnetic resonance. Furthermore, we have measured lifetimes of QD PL for both metamaterial resonances and have found out that the decrease in lifetime (compared to the unstructured reference areas) is more pronounced in the case of the magnetic resonance. Thus, remarkably, the magnetic mode, which exhibits weaker coupling to the far-field (deducted from transmittance measurements) and can be considered as a darker mode, becomes the brighter mode in QD emission due to its higher Purcell enhancement. Our experimental results are in good qualitative agreement with theoretical expectations, paving the way towards an ultimate control of emission by magnetic metamaterials. [1] M. Bayer et al., “Inhibition and enhancement of the spontaneous emission of quantum dots in structured microresonators”, Phys. Rev. Lett. 86, 3168 (2001) [2] P. Lodahl et al., “Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals”, Nature 430, 654 (2004) [3] K. Tanaka et al., “Multifold enhancement of quantum dot luminescence in plasmonic metamaterials”, Phys. Rev. Lett. 105, 227403 (2010) [4] H.N.S. Krishnamoorthy et al., Science 336, 205 (2012)

Metamaterials are capable of realizing exotic electromagnetic phenomena that are either extremely difficult or impossible to accomplish by using naturally occurring materials. In order to develop high performance metamaterials and devices towards many practical applications, a few severe issues have to be resolved, including the strong frequency dispersion and high losses. However, one may also take advantage of the frequency dispersion and losses to realize novel electromagnetic functionalities. A good example is the development metamaterial perfect absorbers where the loss is beneficial. Although the impedance matching to free space has been believed to involve and rely on magnetic resonant response, recently we developed an alternative theoretical model based on cavity resonance and interference. The theory treats a planar metamaterial as a meta-surface that dramatically modifies the transmission and reflection properties at the interface of two neighboring media. We found that the near-field interaction between the metallic layers is largely negligible, and they are only linked by multiple reflections forming a Fabry-Perot-like cavity. This theory successfully explains almost all of the experimental and numerical observations including the thickness dependent of absorption as well as the anti-parallel surface currents. Based on this theory we have demonstrated metamaterial antireflection coatings that are capable of completely eliminating the reflection and significantly enhancing the transmission. We also investigated the impact of resonator geometry and its weak coupling with the ground plane on the performance of metamaterial absorbers, and found that the thickness of ultrathin metamaterial perfect absorbers can be further reduced through modifying the geometric dimensions of the resonators. When the coupling between the resonator array and ground plane is taken into account, the theoretical results from the interference theory are in excellent agreement with experiments and numerical simulations. Finally, we explore the additional application of such metamaterial cavities for polarization control. We demonstrated, both numerically and experimentally, very high efficiency and broad band polarization converters.

The threading dislocation in GaN/InGaN MQWs grown under controlled conditions can result in inverted hexagonal pits (IHP) of 50-70 nm at the surface of the semiconductor, which can be backfilled with 15-30 nm metal nanoparticles [1] to realize a novel class of nanoscale meta-material. The metal nanocrystals (MNC) of Au, Ag, or Pd embedded within the two-dimensional electron gas of strained InGaN MQWs using novel surface engineering has been used to realize a new class of nano-capacitors and nano-acoustic device. Unlike most plasmonic or metal-optic photonic system with the metal nanoparticles at the surface, in the designed structures, the localized field due to the metal nanoparticle interact with the 2D excitons [2] and zone-folded coherent acoustic phonons (ZFLAP) generated within the MQW. The size of the MNCs are designed to avoid any resonant localized surface plasmon interaction due to femtosecond laser excitation. The MQWs were grown using metal oxide chemical vapor deposition, and the surface polarity of the GaN surface was utilized to localize the MNCs within the IHPs. Time-resolved femtosecond pump-probe spectroscopy using a Ti:Sappire laser oscillator and regenerative amplifier was utilized to generate ZFLAP within the MQW InGaN semiconductor structures. [3] Nano-acoustic waves are generated due to the modulation of the piezoelectric field generated to the lattice mismatch in InGaN MQWs in the THz domain. The frequency of the ZFLAP oscillations reduces from 0.8 THz in InGaN MQWs to ~ 0.22 THz in the presence of Au nanoparticles in the MQWs. This change is due to the change in the piezoelectric field in the presence the metal nanoparticles induced by electrostatic image charge effect. The metal nanoparticles embedded within the IHPs also act as nanocapacitors and results in charge storage within the InGaN MQWs. A significant shift in the emission and absorption band-edge of the MQWs is also observed due to the presence of the MNCs. The shift can be controlled with either resonant plasmonic or off-resonant image charge effect [2]. The quantum-confinement stark effect (QCSE) due to presence of the image charge effect is observed which offers the potential to develop novel metal-optic light modulators. In conclusion a novel hybrid semiconductor quantum well based nanoscale meta-material system with multifunctional properties has been realized that can be used to control the flow of electron, photons and phonons in the subwavelength limit. 1. S. Pereira, M. A. Martins, T. Trindade, I. M. Watson, D. Zhu,and C. J. Humphreys, Adv.Mater. 20, 1038 (2008). 2. A. A. Krokhin, A. Llopis, J. Lin, S. M. S. Pereira, M. A. Martins, I. M. Watson and A. Neogi 4th Int. Congress on Adv. Electromagnetic Materials in Microwave & Optics, Karlsruhe, Germany, (2010). 3. M. Mahat, A. Llopis, R. D. Schaller, I. Watson, S. Periera and A. Neogi MRS Communications, 2 , 55, 2012,

We describe circuit level integration of nano-optomechanical systems that comprise of on-chip grating couplers, waveguide, and optomechanical cavities. This photonic circuit platform allows large scale co-integration of nanomechanical resonators with low modal volume, high Q optical cavities. In this talk, we will present extreme scaling of two types of mechanical resonators: the first type has circular symmetry and couples to whisper-gallery cavities; the second type takes beam shape and couples to nanophotonic defect cavities. We have advanced both types of optomechanical resonators to above GHz frequencies with high quality factors and high transduction sensitivities of 6.4am/Hz^1/2. The resonator mass has been simultaneously reduced to below 20fg.

By embedding appropriately designed resonators in the host, two dimensional (2D) chiral elastic solids have been proved to be able to achieve elastic metamaterials with simultaneously double negative properties. Owing to the unique mechanism of coupled translational and rotational resonances specific to the 2D chirality, elastic metamaterial made of pure solid material can be expected which contains only one type of resonator[APL,98,251907]. However, some characteristics of the chiral elastic metamaterial are found outside the classical elasticity. In this work, a 2D ideal discrete model for the chiral elastic metamaterial is constructed to analytically clarify this problem. The discrete dynamic equation is derived and then homogenized to give the continuous description of the metamaterial. The homogenization procedure is validated by the agreement of the dispersion curve of the discrete and homogenized formulations. The form of homogenized governing equations agrees exactly with that of the 2D chiral micropolar solids. In the environment of acoustic fluid, the chiral elastic metamaterial functions like a classical one with simultaneous negative bulk modulus and density, while interacting with solids, unusual phenomenon such as mixed longitudinal and transverse wave modes can be observed. The results suggest that 2D chiral micropolar theory constitutes a suitable macroscopic framework for the theory development of chiral metamaterials, and richer wave phenomenons can be expected.

Soft materials have traditionally been exploited to design and fabricate passive devices - such as tires, shock absorbers and vibration dampers. Here we show that they are excellent candidates to make active devices, as these materials can substantially change shape and volume in response to diverse stimuli. While the mechanical attributes - such as energy absorption, stiffness and thermal properties - of structures with purposeful designed patterns have been widely investigated, we demonstrate that such structures provide great opportunities also for manipulation of sound and light and for a new generation of sensors and electronic devices. Moreover, although instabilities have traditionally been viewed as an inconvenience, we show that they can be exploited to create materials with novel and switchable functionalities.

Piezoelectric materials such as PZT respond with induced mechanical strain when a voltage is applied across them, and vice-versa. This property is made use of in various devices such as sensors, medical imaging and therapy transducers, and hydrophones. Optimal conversion of electrical energy into mechanical energy and vice-versa is realized by matching the acoustic impedances of the transducer element and the imaging medium. In this work, we present a piezoelectric metamaterial, based on our previous work in acoustic cloaking, which has elastic and inertial properties close to those of water. Its effective density is equal to that of water. Its elastic tensor is isotropic and its bulk modulus is with a few percent of the bulk modulus of water, and its shear modulus is two orders of magnitude smaller than its bulk modulus. Such a material is nearly impedance matched with water, and its shear mode behavior is widely separated from the acoustic modes. This material is a composite material, constructed out of PZT, with unit cells consisting of thin struts forming an isotropic force network which provides the effective elastic properties and nodal masses which control effective density. We study the performance of this material, using time domain finite element simulations carried out using our commercial finite element code PZFLEX. Simulations using 1) homogenized material description and 2) explicit modeling of the microstructure are presented. We close by identifying further directions for analysis and discuss other applications of this approach.

The explosion of interest in metamaterials is due to the dramatically increased manipulation ability over light as well as sound waves. These novel materials promise a host of exciting applications such as the invisible cloaks. Such a device is proposed to render the hidden object undetectable under the flow of light or sound, by guiding and controlling the wave path through an engineered space surrounding the object. However, the cloak designed by transformation optics usually calls for a highly anisotropic metamaterial, which make the experimental studies remain challenging. We present here the first practical realization of a low-loss and broadband acoustic cloak for underwater ultrasound. This metamaterial cloak is constructed with a network of acoustic circuit elements, namely serial inductors and shunt capacitors. Our experiment clearly shows that the acoustic cloak can effectively bend the ultrasound waves around the hidden object, with reduced scattering and shadow. Because of the nonresonant nature of the building elements, this low-loss (~6 dB/m) cylindrical cloak exhibits invisibility over a broad frequency range from 52 to 64 kHz. We have further investigated the performance of this cloak design under different defect conditions. The controlled defects in the cloak device is introduced during the microcasting process. The measured ultrasound pressure field distribution shows the wave bending and scattering through the modified cloak. By applying the inversed transformation optics of the cloak, the cloak device with defects can be replaced by a new scattering objet with certain material properties mathematically. This finding is confirmed by our numerical simulation results as well. Our study of the defects in the cloak provides some new insight of fault tolerant cloaks of underwater acoustic and high frequency medical ultrasound.

We show that epitaxial superlattices (SL) can be used to nanoengineer the energy landscape that governs the martensitic transformation in shape memory alloys and tune their thermo-mechanical response.We demonstrate the approach using large-scale molecular dynamics simulations of a SL material consisting of alternate layers of a shape memory Ni-rich NiAl alloy and NiAl ordered alloy. The non-martensitic NiAl alloy was chosen to reduce the energy barrier that separates the martensite and austenite phases of the SL and its incorporation leads to a reduction in the thermal hysteresis of the transition. This is a desirable feature in applications involving actuation and our approach represents a generally-applicable and powerful avenue to engineer desired behavior in mechanically active materials.

Recently, alkali halide fibrous eutectics (in particular KCl-LiF and NaCl-LiF) have been proposed and investigated as self-organized metamaterials in the THz or far infrared ranges, relying on their phonon-polariton resonances. [Reyes-Coronado et al., Optics Express 20, 14663-1468 (2012); Foteinopoulou et al., Phys. Rev. B 84 (3), 035128 (2011)]. Potential applications of these kind of self-organized materials depend on the dispersion of the component materials of the eutectic as well as on the size range and order of the aligned microstructure achieved in the growth process. In this study, several fluoride only systems are investigated. The pseudobinary systems LiF-REF₃ (RE = one of the rare earth elements from La to Lu, or Y, respectively) contain one intermediate compound LiREF₄ which melts congruently for the heavier, and incongruently for the lighter RE. All LiREF₄ exhibited complete mutual miscibility, enabling doping of another RE' in the LiREF₄ matrix. A eutectic point exists between LiF and LiREF₄. The preparation of the moisture-sensitive REF₃ is possible by the treatment of commercial RE₂O₃ powders with Ar/HF mixtures at elevated temperatures. Several LiF-REF₃ and REF₃-RE'F₃ phase diagrams were redetermined by differential thermal analysis (DTA) and a thermodynamic assessment of some LiF-REF₃ systems and one ternary LiF-REF₃-RE'F₃ system was performed. Polycrystalline eutectic fibers consisting of LiF particles inside a LiREF₄ matrix were grown by the micro-pulling-down (mu;-PD) method from inductively heated platinum crucibles. The motif size (typically a few µm) could be controlled by the pulling rate: With a comparably slow pulling rate between 15 and 120 mm/h an interpenetrated microstructure of LiF and LiYF₄ is found through SEM observations. At higher pulling rates, from 120mm/h onwards, a fibrilar microstructure of LiF fibers embedded in a LiYF₄ matrix is more likely to happen. SEM images revealed well-ordered regions of 50x100 microns. The periodicity between LiF fibers are in the range between 4.7 microns (15mm/h) and 1.5 microns (300mm/h).

Development of an acoustic leaky wave antenna is presented. The structure uses a one-dimensional composite right/left hand transmission line approach to tune radiation angle as a function of input frequency. An array of acoustically loaded membranes (acoustic masses) and open channels (acoustic shunts) form a structure shown previously to have negative, zero, or positive refractive index, depending on the frequency of excitation. The fast-wave radiation band of the antenna was determined using the acoustic circuit methodology. Angle of radiation of the acoustic waves out of the acoustic shunts was continually scanned backfire-to-endfire, including broadside. Finite element analysis and acoustic circuit analysis were used as predictive tools and showed agreement with experimentally obtained results. Applications of this antenna structure include both source and sensing technologies. [Work is supported by the Office of Naval Research.]

Structures designed for negative refraction at specific optical frequencies are promising for sub-wavelength focusing, planar lenses and integrated optics. Photonic crystal approaches provide an alternative to high-loss metallic metamaterials. The 2D arrangements predominantly explored have been square and hexagonal crystals. Stronger light-matter interactions have been predicted for more complex geometries and crystal symmetry reduction can promote negative refraction effects. Advances in colloid synthesis enable a wide range of monodisperse nonspherical shapes as building blocks of photonic materials for anomalous refraction. For instance, dimers with controlled degrees of asymmetry and fusion of the constituent spheres have been self-assembled in experiments via gravitational sedimentation in a wedge-shaped confinement cell. The states formed can be described as centered-rectangular for in-plane oriented particles, quasi-2D hexagonal rotator, and hexagonal crystal for out-of-plane oriented particles. Here, negative refraction in the centered-rectangular monolayer case will be discussed for asymmetric dimer tilings. The effects of high-dielectric filling fraction, lobe symmetry, lobe fusion and dielectric contrast will be highlighted. For example, the analysis of equifrequency contours indicates negative refraction for the second photonic band when lobes are highly fused and moderately asymmetric and the particles are separated in air matrix. The infinitely extended 2D analogous structure supports right and left-handed negative refraction in the first two bands.

Recent advances in optical nanostructures provide a variety of new materials having unique dispersion characteristics in frequency and spatial domains. Photonic crystals have various band structures and dispersion properties. Plasmonic metamaterials allow very broad, subdiffraction-limited dispersion spaces and their active modulation. The rich properties of refraction and diffraction in such optical metamaterials enable negative refraction, subwavelength imaging, and many special devices by using transformation optics [1-4]. Here, we exploit those unusual optical properties for enhancing volume diffraction response throughout the nanostructured optical media. Volume diffraction is a macroscopic diffraction phenomena occurring in a thick volume of photosensitive media [5]. It forms a basis of holography, which is widely used in arts and information technology covering telecommunication, storage, and display [6, 7]. By carefully designing phase matching conditions over the dispersion equifrequency surfaces, high resolution and active/passive diffractive elements become possible. 1. J. Li, S. Han, S. Zhang, G. Bartal, and X. Zhang, Opt. Lett. 34, 3128 (2009) 2. Z. Liang, and J. Li, Opt. Exp. 19, 16821 (2011) 3. S. Han, Y. Xiong, D. Genov, Z. Liu, G. Bartal, and X. Zhang, Nano Lett. 8, 4243 (2008) 4. X. Ni, S. Ishii, M. D. Thoreson, V. M. Shalaev, S. Han, S. Lee, and A. V. Kildishev, Opt. Express, 19, 25242 (2011) 5. J. W. Goodman, Introduction to Fourier Optics, Roberts & Company Publishers (2005) 6. S. Han, B.-A. Yu, S. Chung, H. Kim, J. Paek, and B. Lee, Opt. Lett., 29, 107 (2004) 7. B. Lee, S. Han, Y. Jeong, and J. Paek, Opt. Lett., 29, 116 (2004)

3D metallic nanostructures offer unique light-manipulation functionalities for nanophotonics, including isotropic magnetic optical response, engineering of the complex polarization state of light, and, importantly, integration of metamaterials on a chip. Different approaches for the fabrication of 3D metal nanostructures have been demonstrated so far, including direct laser writing (DLW) in combination with a metallization procedure [1], membrane projection lithography (MPL) [2], multistep electron-beam lithography (EBL) [3], and electron-beam deposition (EBD) [4]. However, the fabrication of designed 3D metal nanostructures still poses a major challenge: Feature sizes obtained by DLW or MPL based methods are still too large for applications in the near-infrared spectral range, multistep EBL approaches are limited to few stacked layer geometries, and EBD methods suffer from a poor optical quality of the deposited metal. Here we suggest and demonstrate a novel hybrid fabrication approach combining DLW with EBL metal nanostructure fabrication. This approach makes use of the 3D writing capability of DLW, while preserving the small feature sizes, the capability of selective metallization, and the excellent gold quality of standard EBL based fabrication schemes. It thereby allows for fabrication of high-quality 3D metal-dielectric nanostructures for photonic applications in the near-infrared spectral range. Using this approach, we have fabricated high-quality 3D photonic metamaterial structures and have demonstrated their unique optical properties paving a road to unique functionalities not achievable by other methods. In our work we focus on two prominent structures: The first structure consists of arrays of upright-standing split-ring resonators, which can be used as fundamental building blocks for isotropic photonic metamaterials and for metamaterials integrated with waveguide architectures. The second key structure we have realized is an array of curved metamaterial gap nanoantennas. Such nanoantennas can be used to exploit magnetic coupling effects between the elements of arrayed Yagi-Uda type nanoantennas. Furthermore, they have the potential to provide direct coupling of nanoantenna enhanced radiation from quantum emitters to optical waveguides. We have characterized these structures using linear-optical transmittance spectroscopy revealing their characteristic plasmonic resonances, and demonstrating that our approach offers unprecedented opportunities for the creation of advanced 3D photonic nanostructures at optical frequencies. [1] J.K. Gansel et al., “Gold Helix Photonic Metamaterial as Broadband Circular Polarizer,” Science 325, 1513 (2009). [2] D.B. Burckel et al., "Micrometer-Scale Cubic Unit Cell 3D Metamaterial Layers," Adv. Mater. 22, 5053 (2010). [3] N. Liu et al., “Stereometamaterials,” Nature Photon. 3, 157 (2009). [4] I. Utke, et al., “Focused electron beam induced deposition of gold,” J. Vac. Sci. Technol. B 18, 3168 (2000).

Electromagnetic wave steering and routing around a sharp corner has significant applications in compact electronics and on-chip photonics. However, traditional methods utilizing tapered waveguides or gradient refractive index (GRIN) typically require several-wavelengths-long transition region around a relatively large bending radius. Here we adopt our previously proposed area-preserved nonmagnetic transformation optics strategy to bend electromagnetic waves around a sharp corner with high transmission. Because of the nonmagnetic nature, the designs with this particular transformation optics strategy can be implemented with dielectric materials directly without sacrifice in wave transmission performance. Experiments at both microwave and optical frequencies are demonstrated to prove the efficiency of this novel strategy.

Spectroscopic imaging and focusing through metal nanocolloid solutions is complicated by nonlinear effects such as thermal lensing and plasmonic scattering events. Here, we study the interference patterns generated by multiply-scattered light from disperse gold nanocolloid solutions and investigate the underlying physical principles that lead to the interference patterns, which are useful for the characterization of materials and the interactions between elements in the system [1]. Secondly, we study the dependence of ions in the solution, that cause additional changes in the diffraction patterns. We observe opaque lensing [2,3], which is when the light performs random walks while the wavefront shape appears to focus as a function of propagation. These investigations lead us to propose that focusing through nonlinear scattering materials is controllable not only via pulse shaping but by using external magnetic fields, temperature, concentration, intensity, and other material variables. In the present work we demonstrate the virtual aperture changes of an opaque lens from a gold nanoparticles solution, which changes not only with nanocolloid concentration, incident light intensity or using external magnetic fields but also with the presence of different compounds such as acids and salts (HCl, NaNO3). 80nm diameter gold nanoparticles are placed in a silica container to generate a diffraction pattern by pumping 532nm light pulsed at 300fs. We control the divergence of the diffraction pattern using the sample thickness, concentration, and the intensity of the laser. When we include a different compound in the solution the pattern generated experimentally acts as a virtual aperture for the new diffraction pattern. To summarize we have experimentally demonstrated a virtual aperture for diffraction from an opaque lens with the presence of different solutions. This system, apart from fundamental interest, has promising applications in sensor technology. We propose to control the virtual aperture in the opaque lens using different variables in the solution with the nanoparticles. The ability of change the circular aperture for diffraction by illuminating with a pulsed-laser beam [4] opens the door to have configurable lens with multiple applications as a sensor and characterization technology of materials, understanding the changes in the diffraction pattern. References [1] J L Domínguez-Juárez, et al, “Molecular chi;(2) gratings via electron-beam lithography“, Appl. Phys. Letters, 2010. [2] I M Vellekoop et al,“ Focusing coherent light through opaque strongly scattering media,” Optics Letters, 2000. [3] C Yao, et al, “Controlling the diffused nonlinear light generated in random materials”, Optics Letters, 2012. [4] Min Gu, et al, “Fresnel diffraction by circular and serrated apertures illuminated with an ultrashort pulsed-laser beam,” J. Opt. Soc. Am. A, 1996.

We introduce a new class of optoplasmonic atoms and molecules that combine the capability of optical microcavities to insulate molecule-photon systems from decohering environmental effects with the superior light nanoconcentration properties of plasmonic nanoantennas. Discrete networks of optoplasmonic elements were experimentally realized through a combination of top-down fabrication of plasmonic nanoantennas with a convective self-assembly of dielectric optical microcavity resonators. This approach facilitated a controllable vertical and horizontal positioning of plasmonic nanoantennas relative to whispering gallery mode (WGM) microspheres with a diameter of approximately 2 microns in an on-chip platform. The plasmonic nanostructures were positioned at pre-defined locations in or close to the equatorial plane of the dielectric microspheres where the fields associated with the plasmonic modes can synergistically interact with the evanescent fields of the WGMs. We characterize the optical responses of discrete optoplasmonic networks and demonstrate that the plasmon modes of the metal antennas couple to the photonic modes in the WGM resonator. The latter facilitates a very effective reshaping of the near-field in the surrounding of the metallo-dielectric hybrid system. The potential of the new metamaterials for realizing device functionalities, such as active switching, multiplexing or demultiplexing, is discussed.

The ability to tune the spectral response of metamaterials is considered as one of the most significant developments in the field and provides an effective route to practical application of metamaterials and plasmonic structures. An important way of realizing tunable optical metamaterials is the use of liquid crystals (LC) which exhibit large optical anisotropy and electric field sensitivity[1]. Indeed the large change of refractive index in nematic LCs due to molecular re-orientation caused by external electric fields has already been utilized to control the transmission through LC infiltrated plasmonic structures[2,3]. However, when the dimensions of the individual meta-atoms become comparable to the size of the LC molecules, which is particularly the case for optical metamaterials, the effects of molecular anchoring to the nanostructured surfaces becomes important. This naturally has a significant impact on the tunability of the metamaterial. Here we study the effect of LC alignment and anchoring on the tunability of optical magnetic metamaterials both experimentally and numerically. We use magnetic optical metamaterial built from split-ring-resonator (SRR) meta-atoms and show how the application of an external electric field induces controlled re-orientation of the LC molecules. We fabricate a SRR-metamaterial operating at optical frequencies and infiltrate it with nematic LC to tune the optical response by re-orientation of the LCs. This is achieved by applying a bias electric field while measuring the optical transmittance spectra of the metamaterial. Additionally, the effect of the LC infiltration and tuning is simulated numerically. The LC-director distribution is obtained as numerical solution of the discretised dynamic Euler-Lagrange equation using the MacCormack method[4]. The initial distribution due to boundary conditions and the applied electric field is obtained as equilibrium solution of both the generalised Poisson equation and the Euler-Lagrange equation. The resulting LC-director distribution is then self-consistently coupled to a finite integration time domain Maxwell solver. Comparison between simulation and experiment then allows for a deeper understanding of the influence of the optical fields on the liquid crystal directors and, hence, on the tuning mechanism for metamaterials. [1] I. C. Khoo et al.,”Nanosphere dispersed liquid crystals for tunable negative-zero-positive index of refraction in the optical and terahertz regimes,”Opt. Lett. 31, 2592 (2006). [2] P. R. Evans et al.,” Electrically switchable nonreciprocal transmission of plasmonic nanorods with liquid crystal,” Appl. Phys. Lett. 91, 043101 (2007). [3] W. Dickson et al.,”Electronically Controlled Surface Plasmon Dispersion and Optical Transmission through Metallic Hole Arrays Using Liquid Crystal,” Nano Lett. 8, 281 (2007). [4] T. J. Chung, “Computational fluid dynamics”, Cambridge University Press, Cambridge, 2002.

Plasmonic has emerged as an exciting and promising research era that enables a wide range of optical phenomena. Composite metal-dielectric micro and nano structures have been designed for diverse applications in Optical nano-circuits, efficient solar cells and ultra-sensitive sensors. Plasmonic antennas, as an essential part of an optical system, should efficiently interface emitted/received light beam to free space/optical system. For instance, they can be integrated with a laser source to collimate the emitted beam for efficient source power coupling. Also, absorbed power enhancement in solar cells can be achieved using plasmonic antennas. Previously, circular concentric metal gratings have been used to manipulate the facet of a quantum cascade laser (QCL) and improve its beam divergence. Here, we propose an alternative approach to engineer the QCL facet with enhanced radiation performance. We present a metasurface consist of a 2-D array of plasmonic patches enabling emitted light beam collimation. Holography theorem is used to obtain the interference pattern of the available source (QCL aperture) and the desired radiated beam (narrow beam at an arbitrary direction). The calculated interference pattern is realized by manipulating the surface impedance of a planar dielectric with subwavelength metallic patches. First, the surface is discretized to square regions with subwavlength dimensions (building blocks). Then, a metallic patch is placed on top of the dielectric surface in each of these building blocks. One can obtain the required surface impedance at each building block by changing the corresponding patch size. To illustrate this approach, we design a metasurface hologram on the facet of a QCL aperture to reduce the divergence angle of the beam radiated at broad side. The operating wavelength is 8.06 µm and the metasurface hologram dimensions are 10 by 20 wavelengths. A circular grating structure with the same size (10 grooves) is also designed and simulated for comparison. While the shape of both patterns are similar (semi-circles around the QCL aperture), one can observe binary surface modulation in circular groove structures compared to roughly sinusoidal surface modulation in metasurface hologram. Simulation results show enhanced beam collimation and reduced background optical power compared to circular grooves structures. Specifically, vertical and lateral divergence angles are 5.1 and 7.2 degrees (Reduced by 0.7 and 3.2 degrees compared to the similar circular grating structure). These divergence angles correspond to 20.8 dB antenna gain which is 1.8 dB gain improvement compared to the circular grating structure. Also, the optical background is decreased at least by 3 dB. The holography design approach offers a systematic and robust way to manipulate the radiated beam of light sources into a desired shape for any specific application.

The Mie theory for electromagnetic scattering at subwavelength objects has been established for more than one century, it however likes a black box offers little physical insights into the phase shift associated with the scattering. By viewing the structure as a resonator, and correlating the scattering to the coupling of external waves with leaky modes of the object, we successfully elucidate the scattering phase. We demonstrate that the phase shift can be intuitively understood as resulting from the propagation of light in the leaky modes and bear straightforward relationship with the mode number and the order number of the modes. And most of important, we directly correlate the value of eigen wave vector of leaky modes to the phase shift. The elucidation of phase information provides much more abundant intuitive physical pictures for the light scattering process than Mie theory did. The new model reveals direct relation between scattering phase and leaky modes of the objects, this makes possible by tuning the leaky modes of the object to engineering the scattering phase for specific requirement. Thus it provides a new pathway for the manipulation of light. This work points toward opening up a new era of phase engineering for the development of novel optical functionality.

Metamaterials offer many properties of which natural occurring materials might not be readily availabe, and soon they have been shown across an enormous span of the electromagnetic spectrum with such flexibility, negative refractive index and invisibility cloaks being two primy examples. However, there is a noticeable lack of demonstrated designs at low frequencies - below 100 MHz. Although metamaterials may still be of use in this frequency range, the main drawback is that dimensions can become impractically large. The development of a new class of metamaterials with a significant reduction in size may create opportunities for low frequency metamaterial-based applications. In this paper, we show that noval magnetic metamaterials with an extremely subwavelength unit cell size (a) can be achieved by utilizing interlayer coupling between two metamaterial layers. A new method for magnetic time domain spectroscopy is utilized to experimentally characterize their magnetic properties. Results from simulations and experiments are in excellent agreement, and the metamaterial size (a) is 700 times smaller than the resonant wavelength (lambda;0) with a reasonable oscillator strength. We outline a path for further miniaturization by incorporating a through hole via connecting the two layers. Simulation indicated that these magnetic metamaterials can be made as small as lambda;0/2000. As a preliminary verification, we connected the top to the bottom layers by drilling a hole through the metamaterial and soldering a wire to each side. Our structures maintained their magnetic resonance and had a physical size 1321 times smaller than lambda;0. To the best of our knowledge, the extremely sub-wavelength size (lambda;0/a) of this metamaterial spiral is smaller than any previously published values of any metamaterials. The size of this design allows metamaterials be operated at low frequencies with a compact size. Reference: W.-C. Chen, C. M. Bingham, K. M. Mak, N. W. Caira, W. J. Padiila, " Extremely subwavelength planar magnetic metamaterials", Phys. Rev. B 85 Rapid Communication, 201104, (2012)

Hyperlens has excited a great deal of interest in recent years, not only because of the intriguing physics but also for its ability of imaging sub-diffractional scale objects into the far-field in a real-time fashion. The major breakthrough emerged with the concept of optical hyperlens, showing the first proof-of-principal for magnifying sub-diffractional images to the far-field as propagating waves. Utilizing alternating dielectric and metallic multilayers in a curved geometry, this metamaterial-based optical device achieves strong optical anisotropy that supports the propagation of waves with very large spatial frequency and, due to the cylindrical geometry, adiabatically compresses its lateral wave vector while the wave propagating outward along the radial direction. Consequently, the sub-diffractional details of objects are magnified and eventually larger than the diffraction limit to be transmitted to the far field. Since the first experimental demonstration of the cylindrical hyperlens in one dimension, newly improved designs as well as fabrication techniques, such as the impedance matched, flat, oblate, the aperiodic and acoustic hyperlens, have been proposed in the framework of transformational optics. Nevertheless, all the experimental demonstrations of hyperlens so far were limited to the one dimensional magnification and ultra-violet (UV) wavelengths whereas for any practical imaging applications, it is critical to demonstrate the two-dimensional imaging with resolution below diffraction limit at visible spectrum. Here, we present a spherical hyperlens for two-dimensional sub-diffraction limited real-time imaging at visible frequencies without the need of optical scanning or image reconstruction. [1] Designing a spherical hyperlens with flat hyperbolic dispersion that supports wave propagations with very large spatial frequency, and yet same phase speed, we are able to faithfully resolve sub-diffractional features down to 160 nm, much smaller than the diffraction limit at visible wavelength of 410 nanometers. Such a hyperlens can readily be integrated in conventional microscopes, critically expanding their capabilities beyond the diffraction limit and opening a new realm in real-time nanoscopic optical imaging of biological machineries in living cells. References: [1] Rho, J., Ye, Z., Xiong, Y., Yin, X., Liu, Z., Choi, H., Bartal, G. and Zhang, X. Nature Communications, 1: 143, (2010).

A new series of metal chalcogenides have been synthesized by solid state reactions at 800 oC. The compound adopts a new three-dimensional framework crystallizing in a non-centrosymmetric structure. These materials are transparent in the infrared range with the band gap falling between 2.8 and 1.5 eV. The SHG measurements displayed the strong signals as compared with the commercial AgGaSe2 non-linear optical crystals.

Widespread adoption of metamaterials has been prohibited by reliance on expensive fabrication method. In this paper, we present a low-cost route to fabrication of metamaterial structures on flexible substrates for conformal applications. The targeted frequency range is RF to microwave. The ability to construct metamaterials on a flexible substrate in a cost-effective manner presents advantages in numerous applications, such as automotive radar, defense, and homeland security application. The approach begins with a copper foil applied directly to flexible substrates such as fabric and polyimide and patterned through a photolithographic process. The fabrication process does not require a clean room and uses readily available chemicals and materials. The designs implemented included arrays of elements resonant in the single Gigahertz range. Structures were simulated in Ansoft HFSS, and the results were experimentally verified by measuring the S-Parameters of a system of two antennae separated by a layer of metamaterial.

With potential applications that include cancer treatment, optical computing, biological labeling, and energy harvesting, metal nanoparticles currently rank among the most studied materials in optics. There is increasing interest in characterizing its nanoplasmonic nonlinear optical properties, and several groups [1-5] have attempted to measure the intensity-dependent refractive index n₂ of colloidal Au nanosphere suspensions, primarily through the use of the z-scan technique. The eleven orders of disparity between experimentally-derived values of n₂ suggest that the nonlinear optical characterization of nanocolloids warrant closer inspection. It is suggested that nonlinear thermal self-focusing effects resulting from the high absorption of the nanoparticles and the temperature-dependent refractive index of the solvent limit the application of a z-scan technique for metal nanoparticle solutions. Here, we demonstrate a new method of characterizing the nonlinear optical properties of metal nanoparticle solutions that decouple the thermal and optical nonlinear effects. We examine the far-field interference patterns produced by laser-illuminated samples of 0.05mg/mL 80nm-diameter Au nanospheres in water. By tuning the laser power and repetition rate we alter the peak illumination intensity while maintaining constant average power, and in doing so are able to observe the intensity dependence of the far-field diffraction patterns uncoupled from thermal effects. Our understanding provides a foundation for properly modeling the nonlinear spatial dynamics and associated thermal gradients of light propagation through metal nanoparticle solutions. [1] E. Shahriari, et al., Optics Communications 283, 1929 (2010) [2] X. Zhang, et al., Journal of Nanomaterials 2010, 129067 (2010) [3] T. He, et al., Physics Letters A 373, 592 (2008) [4] L.A. Gomez, et al., Applied Physics B 92, 61 (2008) [5] M.H.M. Ara, et al., Journal of Quantitative Spectroscopy & Radiative Transfer 113, 366 (2012).

We fabricated a thin-film nanostructured Lüneburg lens by patterning a slab of silicon-rods on silicon-on-insulator (SOI) wafer. The refractive index profile of Luneburge lens is achieved by slowly varying the radii of the rods while fixing the lattice period. Due to the fabrication limitation, the height of silicon rods is much smaller than the wavelength; thus wave fields leak into air and substrate, deviating this rod structure from its 2D assumption. To explicitly accounting for this finite slab thickness, a thin-film Luneburg lens has been designed by an all-analytical approach proposed using guidance condition correction. Based on this design, we propose a process flow to implement the nanostructured Lüneburg Lens. The device is patterned by e-beam lithography following by reactive ion etching using HBr gas. In order to alleviate the proximity effect, different amount of the electron beam dosage is set over different pattern regions. The filling factor of each fabricated rod lattice is close to our design, and an aspect ratio 10 of the rod lattice structure has been achieved. The measurement is going to be performed on the near-field scanning optical microscope (NSOM).

Metal nano-structures play important role in various areas such as catalysts or in plasmonics field and especially for metamaterial applications. To generate these structures, we direct laser write three dimensional metal structures of tunable dimensions ranging from hundreds of nanometers to micrometers. This technique has many advantages over conventional fabrication techniques that may allow mass production but are either non-controllable, suffer from high cost and low throughput or are limited in two dimensions. Previous direct laser writing techniques resolved these problems but has been mainly used to fabricate polymeric structures. With computer-controlled translation stage and by utilizing nonlinear optical interactions between chemical precursors and femtosecond pulses, we can directly write both connected and/or disconnected metal nanostructures that are embedded in a polymer matrix. We limit the metal-ion photo-reduction process to a focused spot smaller than that of the diffraction-limit to create metal nanostructures in a focal volume. We study the chemistry that effects the photo induced metal growth to generate desirable metal structures. By varying the types of solvent, polymer and the concentration ratio between metal ion precursors and a polymer capping agent, we demonstrate our control over the morphology of the resulting metal structures. Using Z-scan and other spectrophotometric techniques we analyze the mechanism. We plan to create diverse metal nanostructures for a wider range of applications.

Organic-inorganic hybrids of high refractive indices are attracting much attention because of their applications as antireflective coatings, optical waveguides, holographic materials, coatings for plastic lenses, and encapsulants for light-emitting diodes [1, 2]. High bulk formability and hopefully melt-castable properties are desirable when they are to be used in the form of bulk or monoliths. However, melt-castability or thermoplasticity of hybrids, if any, arises from the flexibility of organic polymer components, which results in the loss of thermoplasticity in high fractions of high-refractive-index components, indicating the difficulty in compatibility between thermoplasticity and high refractive indices. We propose a new type of hybrid materials where high refractive indices and thermoplasticity or melt-castable properties are concurrently achieved by employing chemically modified metalloxane polymers without using organic polymers. Titanium tetra-n-butoxide was hydrolyzed in the presence of β-diketones such as 1-phenylbutane-1,3-dione (PhBu13), pentane-2,4-dione (acetylacetone, Pen24), heptane- 3,5-dione (Hep35), 1-(morpholin-4-yl)butane-1,3-dione (MphBu13), and 1,3-diphenylpropane- 1,3-dione (DPhPr13), followed by concentration at 80oC. Concentrated solutions were transparent, viscous and resin-like, a drop of which was placed on an Si(100) substrate and heated at 120 °C for 10 min in an oven. After cooling down to room temperature, whether the product is hard or soft was examined by touching it with forceps. Then the product was heated again at 120 °C for 3 min, and the hardness was checked again with forceps before cooling down in order to examine the thermoplasticity of the product. The samples prepared from solutions containing PhBu13, MphBu13, or DPhPr13, all of which are solid at room temperature, exhibited thermoplasticity, and were yellow and transparent with refractive indices of about 1.7. Metal oxide nanoclusters or metalloxane polymers may be surrounded by β-diketones, being weakly bonded with each other via van der Waals interaction. [1] C. Lü, B. Yang, J. Mater. Chem. 19, 2884. (2009) [2] J. S. Kim, S. Yang, B. S. Bae, Chem. Mater. 22, 3549 (2010)

In the conventional millimeterwave absorber the absorption is dependent on the permittivity and permeability of materials. The absorption frequency and absorption amount is tuned by composition of the materials such as nanoferrites. Metamaterial based absorbers present a new class of material for design of electromagnetic wave absorbers with great flexibility. These absorbers can be designed by engineering shape of the metallic resonator structures on a dielectric substrate. Different choices exist on selection of substrates for example flexible or non flexible substrates. Design frequency can be tuned over wide range simply by changing dimensions of the metallic resonators. These metallic resonators are planar in structure and can be fabricated by standard processes such as optical photolithography. Metamaterial based absorbers can be made frequency and polarization selective. We are investigating metamaterial based absorbers at millimeter-wave frequencies implemented on the flexible polyimide substrate. These millimeter-wave bands are used for various applications such as automotive radar, high speed point-to-point local area wireless network, point-to-multipoint distribution, space born radios, inter satellite link, and imaging. In this meeting we will present development on our metamaterial based absorbers designed at frequencies between 77 GHz to 110 GHz. Absorbers are simulated and optimized using commercially available software (CST microwave studio). Design aspects will be discussed in detail. Absorbers are fabricated using optical photolithography patterning of 200 nm thick gold metal deposited by sputtering. Fabrication process will be presented with greater detail. New design structures which we investigated recently, will be presented showing dual and wider absorption frequency bands. Fabricated absorbers are ultra thin in comparisons to conventional absorbers. Absorbers are measured on custom made Backward Wave Oscillator based spectrometer. Absorptions of 90% to 99% are achieved in measurement. The close agreements between simulation and measurement results indicate possibilities for design of different metamaterial structures and their optimizations toward achieving desired responses.

Paint based materials and paint based fabrication process is investigated for microwave circuits and metamaterials applications. This new material and process is useful for low cost, large area microwave circuits and metamaterial pattern fabrications. Dielectric substrate is grown by painting, drying and repainting several layers of water based low cost latex paint. Substrate dielectric constant is 6.62 and loss tangent 0.09 which are extracted from S-parameter measurement of materials. Conducting silver paint is painted on paint substrate covered with stencil to transfer circuit patterns. The conductivity of silver paint is 3.35×105 S/m measured using four point probe method. Stencil is fabricated on paper using laser cutting machine. Backside ground metal layer was also fabricated by painting conductive paints. We have demonstrated metamaterial based microwave absorbers at X-band frequencies. Peak absorption of 99% is achieved in simulation and measurement. Measured results are in close agreement with simulation results. Study on microwave circuits such as transmission line, filters, and patch antenna using this process will be presented. This material also serves purpose of flexible substrate and is environmentally safe.

We present a whole new approach to generating enhanced THz surface wave and reversed Cherenkov radiation (RCR) using an electron sheet beam bunch moving parallel to and over a half space filled with double-negative metamaterial (DNM). We separate the space into region 1 (x>-d ) and region 2 ( xlE;-d) which are filled with vacuum and DNM, respectively. Here d is the distance between the electron sheet beam bunch and the surface of the DNM. The DNM and the electron sheet beam bunch are characterized by its effective material parameters and its current density, respectively. Thus, we theoretically derive the field expressions for the surface wave in region 1 and the RCR in region 2, respectively and present the results of numerical computation, which show strong enhancements of the RCR and the THz surface wave. The methods presented here to enhance the RCR and the surface wave are discussed in details and then the physical mechanisms for these enhancements are summarized. These strong enhancements of the THz surface wave and the RCR over a narrow frequency band make compact, high-power THz vacuum electron devices and particle detectors feasible. This work was supported in part by the Natural Science Foundation of China (Grant Nos. 60971031 and 61125103), Sichuan Youth Foundation (Grant No. 2010JQ0005), and the Fundamental Research Funds for the Central Universities (Grant No. ZYGX2010X010).

Recently, there has been much interest in developing non-reciprocal devices for silicon photonics. Among the different approaches, non-reciprocal devices using yttrium iron garnet are the most promising as passive (no power consumption), low optical loss solutions with high magneto-optical activity. Substitution of bismuth or cerium at the yttrium site in the crystal lattice enhances the magneto-optical effects in YIG, leading to smaller devices. Fabrication of a resonator based on this principle has been recently demonstrated. We report on Fabrication of bismuth and cerium YIG films deposited by rf sputtering and rapid thermal anneal using a seed layer of undoped YIG. Bismuth YIG films show a very high Faraday rotation for infrared light. The YIG seed layer was grown by sputter deposition of a composite Y-Fe target in an oxygen atmosphere. Plasma power was held at 200W for 15 minutes of deposition, leading to a thickness of 50nm as measured by AFM. After deposition, seed layers were annealed at 825°C for two minutes in an oxygen atmosphere. the seed layer was analyzed by EBSD, SEM, optical microscopy, and AFM. Cerium YIG films were fabricated by co-sputtering of a Y-Fe target and Ce target in an oxygen atmosphere. Films were annealed for 2 minutes in an oxygen atmosphere at several temperatures, with 775°C being the optimal temperature for formation of the garnet phase and minimization of cracking. Bismuth YIG films were fabricated by co-sputtering of individual Y, Fe, and Bi targets in an oxygen atmosphere followed by an anneal at 825°C in oxygen for two minutes. Substituted garnet films were characterized by SEM, AFM, EBSD,ellipsometry, XRD, and Vibrating Sample Magnetometry (VSM). X-Ray Diffraction analysis of the seed layer indicates crystallization into YIG. However, SEM and EBSD analysis of these films showed that not all films of YIG with YIG XRD patterns are completely crystallized. This could affect optical losses and the subsequent crystallization of the substituted YIG films. The films showed an in-plane coercivity of 20Oe and a normal-to-plane coercivity of 40Oe. X-Ray Diffraction shows clear formation of the garnet phase when cerium substituted layer is grown on a seed layer, while the peaks Cerium YIG grown in the absence of a seed layer are less defined. Using optimized seed layers, substituted garnet films were grown. Ellipsometry indicated that the Bi:YIG films are 144nm thick and EDS measured a substitution of approximately Bi:Y 1:6. The films showed an in-plane coercivity of 40Oe and a normal-to-plane coercivity of 60Oe. X-Ray Diffraction data of the Bi substituted films showed that only the film on the seed layer has formed into Bismuth YIG. Faraday rotation measurements showed a rotation of 4000°/cm for 1310nm light.

A blackbody is an idealized object that absorbs all radiation incidents upon it and reradiates energy solely determined by its temperature, as described by Planck&’s law. The phenomenon that material emits light at high temperature is also known as incandescence. The desire to control incandescence has long been a research topic of interest for scientists—one particular theme being the construction of a selective emitter whose thermal radiation is much narrower than that of a blackbody at the same temperature. In this work we demonstrate, for the first time, selective thermal emitters based on metamaterial perfect absorbers. We experimentally realize a narrow band mid-infrared (MIR) thermal emitter. Multiple metamaterial sub-lattices further permit construction of a dual-band MIR emitter. By performing both emissivity and absorptivity measurements, we find that emissivity and absorptivity agree very well as predicted by Kirchhoff&’s law of thermal radiation. Our results directly demonstrate the great flexibility of metamaterials for tailoring blackbody emission. Reference: 1, Liu, X. et al. Phys. Rev. Lett. 107, 045901 (2011).

The recent developments of transformation optics and engineering metamateials have inspired a new generation of novel optical components in various areas. Compared to the optical and the microwave range, imaging at Tera-Hertz (THz) frequencies is still at an early stage of development due mostly to the great paucity of high performance modulator lens. In this paper, we report a systematics study in developing a three dimensional (3D) aberrations-free metamaterials through an integrated approach among theoretical design, numerical simulation, integrated 3D fabrication, and experimental characterization. Particularly, we notice the design of Luneburg lens, which features radially distributed refractive index, exhibits unique capability of focusing the collimated light to a focal point on the spherical surface without subjecting to spherical aberrations. However, the mismatch between its spherical focal surface and planar focal-plane detector array technology restricts its applications in imaging. To address this shortcoming, we applied transformation optics to “compress” the Luneburg Lens&’ spherical imaging surface into a planar one but meanwhile, maintaining its remarkable focusing properties, such as aberration-free imaging characteristics and wide collecting angle. A series of simulations are performed to validate the design of the flattened Luneburg lens. Non-resonant metamaterials are chosen to realize the 3D Luneburg lens and the index variation can be achieved by fabricating “woodpile” structures with varying the dimension of the sub-wavelength dielectric structure. Fabricating Luneburg lenses that are optically large in all three dimensions is demonstrated using micro-stereo-lithography system. Finally, transmission terahertz time-domain spectroscopy (THz-TDS) is employed to characterize the performance of Luneburg lens. We report a systematics study in developing a three dimensional (3D) aberrations-free metamaterials.. To surmount the mismatch between its spherical focal plane and planar focal-plane detector array technology, transformation optics is applied to “compress” the spherical surface to a planar one but maintaining its characteristics of aberration-free and wide collecting angle. 3D Luneburg lens features non-resonant metamaterials with spatially distributed refractive index is realized by using “woodpile” unit cell with varying the dimension of the sub-wavelength dielectric structure. A Projection micro-stereo-lithography system is used to fabricate 3D Luneburg Lens, which is subsequently characterized by the transmission terahertz time-domain spectroscopy (THz-TDS).

We show how one may obtain conical dispersions in photonic crystals at the zone center if we have accidental degeneracy. We further show that such classical wave conical dispersions, usually called Dirac cones, can in some cases be used to emulate a material with an effectively zero refractive index. We show specifically that in two-dimensional photonic or phononic crystals with C_4v symmetry, we can adjust the system parameters to obtain accidental degeneracy so that two-fold degenerate states and a non-degenerate state have the same frequency at the Ι point, thereby forming a triply-degenerate state at the zone center. The band dispersion near the triple degeneracy point comprises two linear bands that generate conical dispersion surfaces and an additional flat band crossing the Dirac-like point where the upper and lower cone touches. If this triply-degenerate state is formed by the degeneracy of monopole and dipole excitations, we show that the system behaves like an effective medium with permittivity and permeability equal to zero simultaneously at the Dirac point and this system can transport wave as if the refractive index is effectively zero. We will show numerical simulation and experimental results in the microwave regime to demonstrate the zero refractive index property. However, not all the triply-degenerate state can be described by monopole and dipole excitations and in those cases, we show that the conical dispersion may not be related to an effective zero refractive index. We also calculated the Berry phase of the eigenmodes in the Dirac-like cone, and we show that the Berry phase is equal to zero for modes in the Dirac-like cone at the zone center, in contrast with the Berry phase of π for Dirac cones at the zone boundary. We will consider the extension of these ideas to elastic waves and generalize these notions from two dimension to three dimension.

We demonstrate the existence of optical topological transition, the optical equivalent of Lifshitz transition in electronic systems, by controlling the topology of the optical iso-frequency curve using metamaterials. In metals, it has been observed that changing the topology of the Fermi surface leads to a dramatic change in the electron magneto-transport properties. We show the analogous effect in optical systems by transforming the topology of the of the optical iso-frequency curve in a strongly anisotropic non-magnetic metamaterial. The metamaterial is composed of alternate layers of a metal (silver) and a dielectric (titanium dioxide) and is fabricated by physical vapor deposition. The change in topology of the optical iso-frquency surface in this metamaterial from a closed to an open geometry leads to appearance of additional electromagnetic states with large wave-vectors. Light-matter interaction is enhanced due to the presence of these metamaterial states, resulting in strong effect on related quantum-electrodynamical phenomena, such as spontaneous emission. We observed a dramatic change in the spontaneous emission characteristics of quantum dots placed in close proximity to the metamaterial when the optical iso-frequency surface in the metamaterial was transformed from a closed ellipsoid to an open hyperboloid.

The polarization state of light can be described by the amplitude and phase relationship in two orthogonal linear vectors at right angles with respect to the propagation direction. Controlling the polarization of light is an important issue in optics. Traditionally a birefringence crystal plate realizes this function by accumulating the phase difference of light in two orthogonal directions along the optical path. Yet in some circumstances, e.g., in integrated optics, the space is extremely restricted. It is therefore necessary to find new approaches to construct a broadband, ultrathin full-functioning wave plates. Here we report a new approach to tune the phase difference in two orthogonal directions, Δphi;, by controlling the time retardation with a metasurface made of L-shaped metallic structures. The time retardation is on femto-second level, which allows to adjust delta phi from -π to π depending on the geometrical parameters of the metallic structure. The important feature of our approach is that the change of Δphi; is realized when the amplitudes in the two orthogonal directions are kept identical, indicating that the states of the modulated light are always located on the surface of Poincaré sphere. This time-retardation-scheme demonstrates a new pathway in manipulating the polarization state of electromagnetic waves. *to whom all correspondence about this report should be addressed.

In electron systems, there are various kinds of topological phases such as quantum Hall systems and topological insulators. The quantum Hall systems are characterized by the Chern number, which is an integral of the Berry curvature of the Bloch wavefunctions over the whole Brillouin zone. It is quantized to be an integer when there is a gap in the band structure. This integer gives a number of topological chiral edge states, and this integer times e^2/h is equal to the quantized Hall conductivity. In insulating magnets, the spin waves (magnons) are bosons, forming a band structure similar to electrons. When we make a magnonic crystal by introducing periodic modulation into a ferromagnet, magnonic bands may open up a gap. In our presentation we propose a magnonic crystal with a band gap, which has topologically protected chiral edge modes for magnetostatic spin waves [1]. The existence of these modes originates from a nonzero Chern integer for the first magnonic band. The magnonic crystal in our presentation is made of two ferromagnets such as YIG and iron, and iron is embedded periodically into YIG. In these edge modes, the spin wave propagates in a unidirectional manner without backscattering. By changing the unit cell size, the proposed magnonic crystal can have the Chern integer equal to zero, one or two, which corresponds to a number of chiral topological edge modes. This is an analog of the integer quantum Hall effect in magnonic systems, and it corresponds to a gapped version of the magnon thermal Hall effect for magnetostatic waves [2,3]. [1] R. Shindou et al., arXiv.: 1204.3349 [2] R. Matsumoto, S. Murakami, Phys. Rev. B 84, 184406 (2011) [3] R. Matsumoto, S. Murakami, Phys. Rev. Lett. 106, 197202 (2011).

Metamaterials are artificial materials obtained by assembling sub-wavelength-size metal nanoparticles, so-called meta-atoms [1], in a crystalline lattice. Ideally, the light should not be able to resolve the underlying structure of this lattice, implying small interparticle distance and likely strong coupling between the meta-atoms [2]. Although much work has been done to achieve metamaterials with truly local effective material properties, many optical metamaterials show a pronounced dependency on the angle of incidence that can be attributed to strong non-local interparticle coupling. Furthermore, current research has been focused on optimization of optical properties of the single meta-atoms, while their mutual arrangement in a crystalline lattice, mostly being limited to square [2] or cubic spatial symmetries [3], remains largely unexplored. Therefore, it is of utmost importance to understand how the lattice geometry influences the metamaterial properties and to suggest a preferable meta-atom arrangement for achieving optical performance with isotropic angular response. Here we study experimentally and numerically the dispersion properties of magnetic optical metamaterials with meta-atoms arranged in different lattice geometries. We show that the five-fold-symmetry quasi-crystal lattices of magnetic meta-atoms enable to achieve isotropic metamaterial response while preserving the strength of the magnetic resonance. This unique feature is due to the lack of a short-range- but with preserved long-range order in the quasi-crystal. In our experiments we fabricate magnetic cut-wire pair type meta-atoms composed of sandwiches of Au-MgF2-Au discs. The meta-atoms are arranged in a 3-, 4-, and 5-fold lattice symmetry. In addition, a random arrangement of meta-atoms [4] is investigated for comparison. We perform angular resolved transmittance measurements of the different lattice geometries as well corresponding numerical simulations. Our results clearly show that coherent coupling between single meta-atoms is suppressed in the quasi-crystal due to the lack of short-range order. Furthermore, the strength of the resonances is preserved compared to the other crystalline lattices and in contrast to the randomised sample. The demonstrated concept of quasi-crystal metamaterials provides a new route for engineering of the spatial dispersion and optical isotropy of metamaterials. [1] C. Rockstuhl et al., "Scattering properties of meta-atoms," Phys. Rev. B 83, 245119 (2011) [3] M. Decker et al., “Retarded long-range interaction in split-ring-resonator square arrays," Phys. Rev. B. 84, 85416 (2011) [2] J.D. Baena et al., "Towards a systematic design of isotropic bulk magnetic metamaterials using the cubic point groups of symmetry," Phys. Rev. B 76, 245115 (2007) [4] C. Helgert et al., "Effective properties of amorphous metamaterials," Phys. Rev. B 79, 233107 (2009)

Designing and engineering of novel carbon nanotube-based optoelectronic devices needs a thorough microscopic understanding of the ultrafast relaxation dynamics of non-equilibrium charge carriers. From theoretical work, it is known that the scattering via Coulomb interaction and optical phonons takes place on a femtosecond timescale (e.g. [1]). The contribution of acoustic phonons, however, has not been investigated yet. In this work, we perform two-color pump-probe experiments to determine the decay behavior of (8,7), (10,2), (11,3), and (12,1) nanotubes [2]. The E11 and E22 transition energies of these tubes were assigned within photoluminescence excitation spectroscopy. To excite excitons resonantly, pump pulses with energies corresponding to the E22 transition energy of the studied tubes are chosen. The exciton energies are strongly depending on the dielectric screening which has be taken into account in our experiments. The dynamics of the differential transmission (DT) signal is measured with weak probe pulses at energies corresponding to the E11 transition energy of the same tube and three different decay times are found: the fastest decay t1 is in the range between 6 and 15 ps followed by a slower component t2 around 50-100 ps, and the slowest component in the nanosecond range. We perform microscopic calculations based on density matrix formalism. We resolve the non-equilibrium carrier relaxation in momentum and time by deriving Boltzmann equations driven by scattering of electrons with acoustic phonons. To model the described pumpminus;probe experiment, we create a nonequilibrium carrier distribution via optical excitation of charge carriers into the second conduction subband corresponding to the E22 transition. The numerical calculations give relaxation times of few picoseconds, which are in good agreement with the fast exponential decay t1, obtained in the experiment. Additionally, the theoretical calculations result in a decrease of the relaxation time with decreasing tube diameter [2]. This predicted diameter dependence of the picosecond relaxation time is a very interesting result that should stimulate further experimental and theoretical investigations. [1] M. Hirtschulz, E. Malic, F. Milde and A. Knorr, Excitation-induced dephasing and ultrafast intrasubband relaxation in carbon nanotubes, Phys.Rev. B 80, 085405 (2009). [2] O.A. Dyatlova, C. Koehler, E. Malic, J. Gomis-Bresco, J. Maultzsch, A. Tsagan-Mandzhiev, T. Watermann, A. Knorr, U. Woggon, Ultrafast Relaxation Dynamics via Acoustic Phonons in Carbon Nanotubes, Nano Lett. 12, 2249 (2012).

Carbon nanotubes (CNT) can generate sound with smooth spectra by means of thermoacoustics over a wide frequency range (1-10⁵ Hz). However, the low sound generation efficiency of open CNT films at low frequencies (eta; prop;f²), where the demands for large size and flexible sound projectors is high, is frustrating. The nanoscale thickness of CNT sheets, the high sensitivity to the environment and the high surface temperatures required for sound generation suggest some protection of the CNTs is needed, which is here provided by means of encapsulation in inert gases. The observed sound pressure level for the encapsulated transducer (>130 dB in air and >200 dB underwater in near field at distance r=1 cm and >100 dB in air and >170 dB underwater at distance r=1 m) is Q times higher than for open system, where Q is a resonant quality factor of vibrating plates. For the low frequency region we propose another method to increase eta; by a factor of radic;2 by modulation of the applied high frequency carrier current with a low frequency resonant envelope. This method enables sound generation at the frequency of the applied current without the use of energy-consuming biasing. The acoustical and geometrical parameters of resonant systems providing further increase of efficiency and transduction performance will be discussed.

I will present our recent work on transient absorption microscopy (TAM) as a novel tool to image carrier and phonon dynamics in single nanostructures with simultaneously high spatial (~ 200 nm) and temporal resolution (~ 200 fs). Until now, the majority of dynamical measurements on single nanostructures are based on photoluminescence (PL). Transient absorption imaging approach offers two key advantages over PL based methods: 1) A time resolution of ~ 200 fs. This fast time resolution is important because many critical events such as electron-phonon coupling occur on such sub-picosecond time scales. 2) The measured signal is based on absorption, which means we can also study samples with low or even zero fluorescence quantum yield. I will discuss two examples of such transient absorption microscopic studies. Femtosecond transient absorption microscopy was employed to study the excited-state dynamics of individual semiconducting single wall carbon nanotubes (SWNTs). This unique experimental approach removes sample heterogeneity in ultrafast measurements of these complex materials. Transient absorption spectra of the individual SWNTs were obtained by recording transient absorption images at different probe wavelengths. These measurements provide new information about the origin of the photoinduced absorption features of SWNTs. Transient absorption dynamics traces were also collected for individual SWNTs. The dynamics show a fast ~ 1 ps decay for all the semiconducting nanotubes studied. We attributed this fast relaxation to coupling between the excitons created by the pump laser pulse and the substrate. Recent success in fabricating graphene has inspired researchers to search for semiconducting analogues of graphene in hopes to retain 2D crystallinity while providing a bandgap. In particular, monolayer MoS2 has recently emerged as a promising candidate. The second study I will present is the investigation of exciton dynamics in atomically thin and semiconducting MoS2 crystals. By controlling the dielectric environment around monolayers of MoS2 crystals, our measurements provide a comprehensive understanding on intrinsic exciton dynamics, quantum confinement effect, exciton-phonon coupling, as well as how the dielectric environment alters optical properties and energy relaxation processes in these novel 2D crystals.