Laser technology has steadily evolved over the last 50 years since its invention, and has generated a series of ramifications in experimental science. Particularly, lasers have enabled the creation of the shortest man-made event: a femtosecond pulse of electromagnetic radiation. Due to their unmatched spatial and temporal resolutions, femtosecond pulses have been used in a number of techniques to measure properties of individual molecules. One of these techniques is Coulomb Explosion Imaging (CEI), whose purpose is to retrieve the structure of individual molecules. Unlike frequency domain spectroscopy (which is ill-suited to characterize the structure of large molecules due to their complex spectra) and diffraction techniques (which only work if molecules can be locked into a crystallization pattern), CEI provides a direct measurement of the properties of individual molecules, instead of measuring a sample as a whole. This novel technique was first introduced to study molecular structure by colliding a beam of highly energetic ions onto a thin foil. The version of CEI used in this work uses a beam of neutral molecules and replaces the thin foil with femtosecond optical pulses. The introduction of the laser has brought with it the ability to conduct time-resolved measurements of molecular processes (breaking of molecular bonds, internuclear motion, for example) on a femtosecond time scale using pump-probe techniques in conjunction with CEI. Furthermore, CEI is presently the only technique that can discriminate single molecules based on their handedness. I have conducted a Laser Coulomb Explosion Imaging (LCEI) experiment using dicloromethane as a model polyatomic molecule. In order to perform LCEI, an intense femtosecond laser pulse is used to strip away electrons from a molecule and cause it to explode into smaller fragments. Imaging the molecule is done using data collected from its fragments. Thus, in practice LCEI can be seen as a technique comprising an experimental phase (Coulomb explosion) and an analytical phase (imaging). Dichloromethane was chosen for this study to prepare the techniques that are necessary for future experiments on chiral molecules. The experimental setup used for this instance of LCEI is the PATRICK instrument, a combination of high-end vacuum, electronics and laser equipment, which will also be described herein. The rest of this thesis will focus on the results obtained from the computational tools I developed for imaging the CEI data and obtaining physical properties about the exploded molecules. In doing so I have also obtained the first geometrical reconstructions of five atom molecules from CEI data, which will also be given in this study. Though LCEI is a general technique that can be exploited in a variety of different experiments, this particular project was built around the interest of imaging chiral molecules. Unlike mass, multipole moments, polarizabilities and other "conventional" physical properties of molecules, chirality arises solely from spatial symmetry considerations, making it more elusive. For example, in order to experimentally determine the properties of a molecule in the traditional manner, one proceeds by inferring molecular characteristics from general spectroscopic data pertaining to a sample of molecules. In this manner, molecules are ascribed properties based on statistical measurements done on a population. Although statistical methods are also used to measure the handedness of a sample of molecules, it is understood that these measurements yield information only about the sample, but not the individual molecules themselves. Indeed, chirality is not a property of a type of molecule, but of individual molecules, rendering LCEI very suitable to measure chirality. Accordingly, it is the ultimate goal of this thesis to set the stage for future experiments involving the measurement of the handedness of individual chiral molecules.

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.

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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.

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The work in this dissertation has focused on the optical properties of semiconductor microcavities containing one or more high-quality, narrow-linewidth quantum wells, and how the appropriate design and growth of such structures can result in a nonperturbative coupling of light and matter. We apply the term Normal-Mode Coupling to describe this interaction, as it can be ascribed to the dipole interaction lifting the degeneracy between field and emitter resonances, resulting in a strongly coupled two- (or more-) oscillator system. Linear reflection, transmission, and photoluminescence measurements for the two-oscillator systems show two dips or peaks near zero detuning, whereas samples with two nonidentical quantum wells coupled to the microcavity display a three-resonance behavior. It is demonstrated that the linewidths of these samples are not only functions of the uncoupled cavity and exciton lineshapes, but are also sensitive to the local variations of the index of refraction and optical absorption. To this end, absorption measurements of multiple-quantum-well samples lead to a phenomenological derivation of the optical susceptibility inclusive of the influence of structural disorder. Use of this susceptibility in a transfer-matrix calculation then gives good agreement with experiment. The ability to see well-resolved normal-mode coupling peaks at room temperature is also demonstrated. Here, the distributed Bragg reflector mirror layers are created through oxidation of the AlAs mirror layers, resulting in increased field confinement and larger splitting. The superlative splitting-to-linewidth ratios at resonance for these samples make them ideal candidates for nonlinear studies. Pump-probe transmission and photoluminescence studies utilizing both resonant and nonresonant pump excitation are presented. Nonlinear saturation of the quantum-well excitonic resonance leads to increased absorption at the normal-mode coupling transmission peaks, which reduces their amplitude. For relatively small positive cavity-exciton detunings, there is a good correspondence between photoluminescence crossover and the opening up of probe transmission at the uncoupled cavity-mode resonance. It is demonstrated that this occurs when the exciton absorption is bleached, and the coupling undergoes a transition from nonperturbative to weak. In this case, nonlinear absorption measurements on a cavityless multiple-quantum-well sample provide the nonlinear optical susceptibility for use in a transfer-matrix simulation for the off-resonant pumping experiments.