<p> Metamaterials operating at terahertz (THz) region of the electromagnetic spectrum have remained have remained a promising area of study not only for realizing technologies in a historically underdeveloped spectral regime, but also as a scientific tool for exploring and controlling fundamental physical phenomena at meV energy scales in a variety of condensed matter systems. In this thesis, I will present several projects in which metamaterials and more traditional condensed matter systems are integrated into hybrid metamaterial systems. We leverage these systems to realize new practical THz devices, as well as to couple to and control quantum phenomena in condensed matter systems. I will begin with an introduction to the conceptual, numerical, and experimental techniques in the THz metamaterial toolbox. The first research endeavor I will discuss is a metamaterial system that incorporates perhaps the simplest material; air. This metamaterial perfect absorber with a continuously tunable air dielectric layer allows for comprehensive exploration of metamaterial absorber systems, and demonstrates some unique phenomena owing to its lossless dielectric layer. Next I will introduce an applications oriented device; an electrically actuated broadband terahertz switch which transitions from a non-reflective, transmissive state to a fully absorptive state. It employs an all dielectric metamaterial layer to suppress reflections and trap light, and an electrically actuated phase change material, <i>VO</i>₂ to transition between states. The final section of this dissertation will explore strong coupling effects between a metamaterial and the superconducting c-axis Josephson plasmon in the layered cuprate, <i>La_2&ndash;xSr_xCuO₄</i>. Preliminary measurements are first presented then followed by high field THz measurements in which complex nonlinear behavior is observed.</p><p>

Surface Plasmon Polaritons (SPPs) are considered to be attractive components for plasmonics and nanophotonic devices due to their sensitivity to interface changes, and their ability to guide and confine light beyond the diffraction limit. They have been utilized in SPP resonance sensors and near field imaging techniques and, more recently, SPP experiments to monitor and control ultrafast charge carrier and energy relaxation dynamics in thin films. In this thesis, we discuss excitation and propagation properties of ultrafast SPPs on thin extended metal films and SPP waveguide structures. In addition, localized and propagating surface plasmon interactions in functional plasmonic nanostructures will also be addressed. For the excitation studies of ultrafast SPPs, we have done detailed analysis of femtosecond surface plasmon pulse generation under resonant excitation condition using prism coupling technique. Our results show that photon-SPP coupling is a resonant process with a finite spectral bandwidth that causes spectral phase shift and narrowing of the SPP pulse spectrum. Both effects result in temporal pulse broadening and, therefore, set a lower limit on the duration of ultrafast SPP pulses. These findings are necessary for the successful integration of plasmonic components into high-speed SPP circuits and time-resolved SPP sensors. To demonstrate interactions between localized and propagating surface plasmons, we used block-copolymer based self assembly techniques to deposit long range ordered gold nanoparticle arrays onto silver thin films to fabricate composite nanoparticle thin film structures. We demonstrate that these gold nanoparticle arrays interact with SPPs that propagate at the film/nanoparticle interface and therefore, modify the dispersion relation of SPPs and lead to strong field localizations. These results are important and advantageous for plasmonic device applications. For the propagation studies of ultrafast SPPs, we have designed and constructed a home-built femtosecond photon scanning tunneling microscope (fsPSTM) to visualize ultrafast SPPs in photonic devices based on metal nanostructures. Temporal and phase information have been obtained by incorporating the fsPSTM into one arm of a Mach-Zehnder interferometer, allowing heterodyne detection. Understanding plasmon propagation in metal nanostructures is a requirement for implementing such structures into optoelectronic and telecommunication technologies.

We study light propagation in strongly scattering, random photonic materials from material synthesis, sample fabrication, characterization of light propagation and theoretical calculation. Light propagation in random photonic materials is very important not only because the study can lead to better understanding of light propagation in ordered photonic materials (photonic crystal) ( i.e., the best filling fraction in photonic crystal, the coordination number to maximize the photonic band gap, etc.); and also because the light propagation in random materials can lead to fascinating physical problems (i.e., coherent backscattering, Anderson localization, and random laser etc.). For the experiments, we synthesize the high index of refraction core-shell particles (ZnS-shell PS core, micron scale) with sonochemical methods. The smooth random films are fabricated by creating a concave meniscus from the colloidal solution. The structure (characterized by average coordination number Z) of high index particles is tuned by mixing the ZnS-PS with sacrificial PMMA spheres and followed by acetone wash. After the strongly scattering, random films are fabricated, the light propagation is characterized by measuring the coherent backscattering effect to obtain the transport mean free part of 1.06-micron wavelength light. We find a local minimum of l* (∼2.1μm) around Z∼4-5 and the scattering weakened with the increase of Z (Z>5). We show that the experimental results for porous random films disagree with the existing model for diffusive transport in random media. To explain our experimental discovery, we present a modified diffusion transport theory which incorporates the correlation of waves at strong scattering limit and Mie resonance regime to describe our experiments. The model should be useful to find the optimal conditions to enhance the scattering in random photonic materials. Furthermore, we try to enhance the scattering in random photonic materials by changing the size of scatterers, index of refraction and incident laser wavelength not only in theoretical calculation according to our modified diffusion transport theory but also in the experiments. We synthesize high index of refraction material (SnS2, n∼3.0) whose index is characterized by single scattering method. We also synthesize metallic photonic materials (such as Gallium micro-spheres) whose index of refraction can vary dramatically in visible and near infrared regime. All these studies to enhance the scattering could lead to fascinating physical phenomena (i.e. Anderson localization, and random laser etc.).

This thesis reports experimental study of surface plasmon excitations--localized surface plasmons (SPs) and propagating surface plasmon polaritons (SPPs)--and their interactions with dipole emitters CdSe/ZnS (core/shell) nanocrystals. This study will contribute to potential applications of SP-enhanced fluorescent sensors and fast SPP-waveguided electronics. Our angle-dependent, polarization-related extinction spectra show that SPs in 2D nanodisk arrays are not only related to the intrinsic properties of individual nanoparticles, but also dependent on the dipole-dipole interactions among them. SP resonance peaks are red-shifted with increasing incidence angle. As the nanodisk center-to-center distance decreases within sub-wavelengths, coupling to waveguide modes and diffracted evanescent wave modifies the transmission. The out-of-disk-plane dipole surface plasmon resonance is used to couple to nanocrystals and to test the conventional assumption that dipole emission rates are homogeneous in time-resolved photoluminescence (PL) measurements of ensemble samples. Our new finding is that the spontaneous emission rate of dipole emitters deposited on a 2D gold nanodisk array depends on the detection angle and polarization. At the band-edge emission wavelength of nanocrystals, the out-of-incidence-plane, s-polarized PL measurements are detection angle-independent, and the in-plane-of-incidence, p-polarized PL measurements show an additional decay caused by SP-enhanced emission. In planar gold films we perform reflectivity measurements in the Kretschmann-Raether (KR) configuration and determine the frequency- and momentum-dependent SPP resonance. In hybrid samples of planar gold films and semiconductor nanocrystals, the coupling between the dipole emitters and SPPs can generate SPP emission through an inverted KR hemisphere prism. For the first time we observed a decay rate increase of SPP emission as a function of nanocrystals emission wavelength in gold films with silica separation layers, as compared to free-space dipole emission detected in the front of the metal surface. Simulations based on the theory of Ford and Weber show that this increase is primarily due to energy transfer of perpendicular dipoles into lossy surface waves. Our results of polarization-selective and angle-dependent SP-enhanced emission can be used to optimize and tune the performance of light sources or fluorescent sensors. The study of SPP emission will lead to efficient energy transfer in fast plasmonic device applications. Keywords: Au, CdSe/ZnS nanocrystals, SP, SPP emission, nanodisk arrays, time-resolved single photon counting.

<p> To determine the mechanical and optical response of diamond crystals at high stresses and to evaluate anisotropy effects, single crystals (Type IIa) were shock compressed along the [100], [110], and [111] orientations to ~120 GPa peak elastic stresses. Particle velocity histories and shock velocities, measured using laser interferometry, were used to examine nonlinear elasticity, refractive indices, and Hugoniot elastic limits of shocked diamond. Time-resolved Raman spectroscopy was used to measure the shock compression induced frequency shifts of the triply degenerate 1332.5 cm^-1 Raman line. </p><p> Longitudinal stress-density states for elastic compression along different orientations were determined from the measured particle velocity histories and elastic shock wave velocities. The complete set of third-order elastic constants was determined from the stress-density states and published acoustic data. Several of these constants differed significantly from those calculated using theoretical models. </p><p> The refractive index of diamond shocked along [100] and [111] was determined from changes in the optical path length along the direction of uniaxial strain. Linear photoelasticity theory predicted the measured refractive index along [111]. In contrast, the refractive index along [100] was nonlinear. The refractive indices for [110] compression were not determined, but the data showed evidence of birefringence. </p><p> The splitting and frequency shifts of the diamond Raman line were measured for shock compression along [111] and were in good agreement with predictions from prior shock work. Frequency shifts were also measured along [100] and [110] up to ~60 GPa, extending previous measurements. The anharmonic force constants determined from all shock compression measurements agree with the previous shock compression determinations. </p><p> Hugoniot elastic limits for diamond shock compressed along different orientations were determined from the measured wave profiles. The elastic limits for the three orientations were highest at ~90 GPa peak elastic stress, but decreased at the higher peak elastic stress. Shear strengths were determined from the measured elastic limits: shocked diamond was strongest for compression along [110] and weakest for compression along [111]. The shear strength dependence on shock propagation direction was correlated with the stress magnitude normal to the slip plane, which appeared to inhibit the onset of inelastic deformation. </p>

<p> Gyromagnetic phenomena have been of interest since the dawn of modern electromagnetic theory. While rotation-induced magnetization in electronic systems has been known for over 100 years, the phenomenon remains largely unexplored in nuclear degrees of freedom. This thesis explores the influence of external angular momentum on nuclear polarization, utilizing optical fields endowed with orbital angular momentum (OAM). To that end, I employ novel holographic methods to project light fields with programmable OAM content into fluid samples. To quantify the OAM in such fields, I introduce new techniques of holographic video microscopy to characterize optical forces. These optical manipulation and detection schemes are combined with standard NMR spectroscopy to reveal the effects of optical forces on the nuclear hyperpolatization of both absorbing and non-absorbing samples. These experiments provide evidence of a non-resonant coupling between the orbital angular momentum of light and nuclear spins.</p>

<p> This thesis investigates the fundamental nanoscale near-field light matter interaction between a probe tip and plasmonic antenna nanostructures. The thesis is focused on polarization control of metallic plasmon modes using scattering-type scanning near-field optical microscopy (s-SNOM). Part of the thesis is dedicated to spectroscopic near-field comparison of coated and bare single plasmonic particles in the infrared wavelength range (&lambda;= 9&ndash;11 &micro;m) using s-SNOM. By tuning the wavelength of the incident light, we have acquired information on the spectral polarization dependence plasmon modes and plasmon/phonon&ndash;polariton resonant near-field interactions. The enhanced near-field coupling between the probe tip and high index Au nanostructures and Au-core thin silica coating (thickness &ap;10 nm) is described and quantified. </p>

Thesis (Ph.D.)--Lehigh University, 2007.

Thesis (Ph.D.)--Lehigh University, 2008.

<p> The Mott metal-insulator transition (MIT) in transition-metal complex oxides results from strong electron-electron interactions and is accompanied by a rich spectrum of phenomena, including magnetic, charge, and orbital ordering, superconductivity, structural distortions, polarons, and very high-density 2-dimensional interface electron liquids. Recent advances in oxide heteroepitaxy allow interface control as a promising new approach to tuning the exotic properties of materials near the quantum critical point, with potential application to technologies including phase-change electronics, high power transistors, and sensors. The dynamical conductivity of oxide heterostructures is measured using a combination of terahertz time-domain spectroscopy, Fourier transform infrared spectroscopy, and dc magnetotransport. The rare-earth nickelates <i> R</i>NiO₃ (<i>R</i> = La, Nd...) exhibit a temperature and bandwidth controlled MIT in bulk. Measurements of the Drude response in epitaxial thin films provide quantification of the strain-dependent mass enhancement in the metallic phase due to strong correlations. Reduction of LaNiO₃ film thickness leads to additional mass renormalization attributed to structural distortions at the heteroepitaxial interface, and an MIT is observed depending on the interfacing materials in coherent perovskite heterostructures. The rare-earth titanates <i>R</i>TiO₃ exhibit a bandwidth and band filling controlled Mott MIT. Furthermore, the heterointerface between Mott insulating GdTiO₃ and band insulating SrTiO₃ exhibits a 2-dimensional itinerant electron liquid, with extremely high sheet densities of 3 &times; 10¹⁴ cm^-2. The dynamical conductivity of the interface electrons is analyzed in terms of subband-dependent electron mobility and the established large polaron dynamics in bulk SrTiO₃. Additional confinement of the electron liquids is achieved by decreasing the SrTiO₃ layer thickness, with attendant increase in the dynamical mass. Taking the confinement to its extreme limit, a single (GdO)⁺ plane in Mott insulating GdTiO₃ is replaced with a (SrO)⁰ plane. This is equivalent to "delta-doping" the Mott insulator with an extremely high density sheet of holes. The transport and absorption in the resulting two-dimensional insulator are consistent with a simple model of small polaron hopping. A comparison is made to similar features in the conductivity of randomly doped Sr_1-xGd_xTiO₃ films.</p>