Plasmonic metasurfaces enable functionalities that extend beyond the possibilities of classical optical materials and as a result, have gained significant research interest over the years. This thesis aims towards introducing plasmonic metamaterials and metasurfaces, a two-dimensional subset of metamaterials. The thesis also provides insights into the nonlinear optical responses from subwavelength metallic nanostructures manifesting as extraordinary physical phenomena like the second harmonic generation (SHG). The hydrodynamic Drude model is a theory that characterizes electron conduction in a hydrodynamic way to predict optical responses of metals. The thesis discusses the various contributions to the second-order optical nonlinearities from the terms in the hydrodynamic model: Coulomb, convection, and the Lorentz magnetic force. The significance of these terms, specifically the Lorentz magnetic term, is validated in contrast with existing research. The details of the work carried out to achieve a significant contribution to SHG from the Lorentz magnetic term are provided. A dominant Lorentz magnetic force for SHG was achieved through engineering T-shaped aperture arrays milled into a thin gold film. The dimensions of these structures were tuned for fundamental wavelength resonance. The structures exhibit both magnetic and electric field enhancements at the plasmonic resonance. Furthermore, a revised theoretical model is developed to accurately predict both linear and nonlinear optical responses of metamaterials. The model is based on the hydrodynamic Drude model and nonlinear scattering theory. Results from the finite difference time domain simulations performed on the metasurface are presented. It is observed that the T-shaped structure provides 65% greater nonlinear generation from the Lorentz magnetic term than the sum of the other two hydrodynamic terms. The influence of incident beam polarization on SHG conversion efficiency was also investigated. It was discovered that even though the contributions of hydrodynamic (Coulomb and convection) terms are maximum at 0◦ and 90◦, the metasurface shows maximum SHG intensity at 45◦ which indicates a dominant Lorentz magnetic term. Experimental validation was performed using the fabricated metasurface and a good agreement between the experiment and theoretical calculations was observed. Another aspect of the magnetic Lorentz force contribution, Bethe’s aperture theory was evaluated for a circular aperture at off-normal incident light. It is shown that the Lorentz force dominates the SHG by an order of magnitude at angled incidence where the generation is maximized. The angular dependence was observed to match the magnetic and electric dipole interaction effects as predicted from Bethe’s theory. The revised theory developed in this thesis predicts the linear and nonlinear optical responses of metamaterials including their angular dependency. The analysis and numerical calculations for a circular aperture agree well with past experiments. To conclude, the thesis provides an outlook on future developments in the field of nonlinear plasmonic research with regards to the development of highly efficient nonlinear metasurfaces through optimization of the Lorentz contributions. An insight into the recent developments in nanofabrication capabilities, design methodologies, nano-characterization techniques, modern electromagnetic simulations is discussed as avenues for future research in nanophotonic and nanoplasmonic device design and development. / Graduate

L’optique non linéaire est un outil très puissant pour l’étude des propriétés photoniques de molécules, de matériaux et de nanostructures. La taille et la forme des nanoparticules de métaux nobles (NMNPs) influencent fortement leurs propriétés optiques non linéaires du second ordre. Dans cette thèse, nous proposons une étude systématique de l'influence de la surface de nanoparticules sur leurs valeurs de première hyperpolarisabilité bêta. Des nanoparticules en poudre d’argent (de diamètres 7 nm) ainsi que des solutions colloïdales sur NMNPs -avec différentes compositions, tailles et formes -ont été synthétisés : des nanosphères d'argent (de diamètres 10 nm), des nanosphères d’or (de diamètres 3,0; 11,6; 15,8; 17,4; 20,0 et 43,0 nm), des nanobâtonnets d’or (de rapports d'aspect 1,47; 1,63 et 2,30), des nanobâtonnets d’argent (de rapports d'aspect 5,0; 6,3; 7,5; 8,2 et 9,7), des nanofleurs de platine (de diamètres 7,0; 8,0; 10,0; 14,0; 20,0 et 31,0 nm) ainsi que des nanoprismes d'or (d’une longueur de côtés de 47,5 à 112,3 nm). La diffusion harmonique de la lumière (HLS) à 1064 nm est utilisée pour étudier la génération du second harmonique des NMNPs colloïdaux, et d'en déduire leurs valeurs de première hyperpolarisabilité bêta. Pour les nanosphères et les nanorods étudiés dans ce travail, nous démontrons que leurs valeurs de bêta présentent une forte dépendance avec leur surface, qui est le paramètre dominant dans l'évolution des valeurs de bêta. Par ailleurs, la rugosité de la surface des particules ainsi que la forme des irrégularités des nanofleurs sont responsables de valeurs exceptionnellement élevées de bêta. En outre, nous démontrons expérimentalement, pour la première fois dans la littérature, que les valeurs de bêta des nanoprismes présentent non seulement une dépendance linéaire par rapport à la surface, mais sont également sensibles aux courbures des sommets du triangle. / Nonlinear optics is well known to be a highly powerful tool to investigate the photonic properties of molecules, materials and nanostructures. Size and shape of noble metal nanoparticles (NMNPs) strongly influence their second-order nonlinear optical properties. In this PhD thesis, we propose a systematic investigation of the influence of the nanoparticle surface area on their first hyperpolarizability beta values. Powdery-silver nanoparticles (diameters 7 nm) and colloidal solutions on NMNPs with different composition, sizes and shapes have been synthesized, i.e. silver nanospheres (diameters 10 nm), gold nanospheres (diameters 3.0; 11.6; 15.8; 17.4; 20.0 and 43 nm), gold nanorods (aspect ratios 1.47; 1.63 and 2.30), silver nanorods (aspect ratios 5.0; 6.3; 7.5; 8.2 and 9.7), platinum nanoflowers (diameters 7.0; 8.0; 10.0; 14.0; 20.0 and 31.0 nm) and gold nanoprisms (edge length tuned from 47.5 to 112.3 nm). Harmonic light scattering (HLS) at 1064 nm is used to investigate the second harmonic generation from colloidal NMNPs, and to infer their first hyperpolarizability tensor beta. For the nanospheres and nanorods investigated in this work, we demonstrate that their beta values display a strong dependence with their surface area, which is the dominant parameter in the evolution of beta values. Otherwise, particle surface corrugation and shape irregularities of nanoflowers are responsible for exceptionally high beta values. Moreover, we report for the first time in the literature that the beta values of nanoprisms display not only a linear dependence with respect to the surface area, but are also sensitive to the sharpness of the triangle vertices.

<p>Laser-based displays have been under active development over the past 50 years. Visible lasers are considered as the “ultimate” light sources for display applications due to their high brightness, high directionality and high color saturation. Unlike commercially available red and blue laser diodes, semiconductor laser diodes that can directly emit green light with sufficient power and efficiency required in laser display are still not ready yet. Significant effort has been paid around the world to overcome this “green bottleneck”.</p> <p>The aim of this thesis is to investigate a practical solution to build a compact green laser to satisfy the cost/performance requirement for laser display applications. Frequency doubling based on MgO doped periodically poled lithium niobate (MgO:PPLN) is the main research direction of this thesis work.</p> <p>The thesis focuses on several engineering issues, mainly related to practical applications. Two different approaches have been explored: single-pass frequency doubling and intra-cavity frequency doubling. In the single-pass configuration, an all-fiber Q-switched fiber laser was used as the fundamental laser source because the high peak pump power can increase the conversion efficiency. 3.1%/W/cm nonlinear conversion efficiency was achieved which show good agreements with the theoretical simulations. The single-pass frequency doubling of a novel annealing proton exchanged (APE) MgO:PPLN ridge waveguide was also investigated. Over 120 mW green laser with a 53.2% conversion efficiency was achieved. The results have shown remarkable improvements comparing with the reported waveguide devices.</p> <p>On the other hand, in the intra-cavity frequency doubling, Nd:YVO₄/MgO:PPLN microchips for low power (300 mW CW green power and 530 mW modulated green power) applications have been demonstrated experimentally and investigated theoretically. It has been shown that although the plane-parallel cavity structure with discrete components can provide 2.9 W green laser with 29.6% conversion efficiency, it is complex for mass production. One of the important research achievements of this thesis is to study and optimization of a novel monolithically integrated Nd:YVO₄/MgO:PPLN module (namely mGreen module) which combines the advantages of the microchip structure and the discrete plane-parallel cavity structure. 1.28 Watt output green laser has been achieved through a compact configuration based on the optimized mGreen module. Power scaling based on this monolithic green laser module by employing an array concept has also been investigated. The dependence of output power on pump beam gap has been studied both theoretically and experimentally.</p> / Doctor of Philosophy (PhD)

In this dissertation, the laser spectroscopic methods, second harmonic generation (SHG) and ultrafast transient absorption, have been employed to study the reactions and dynamics in two different types of materials, namely, silver nanoparticles and micro-sized ultrathin crystalline oligoacenes. These two materials, although both are in small dimensions, represent two distinct types of systems with divergent characteristics: 1) systems in which interactions at the surface/interface are dominant, and 2) systems in which bulk interactions are dominant. Silver nanoparticles are an important member of the class of noble metal nanoparticles, and possess unique optical and chemical properties due to their ultrafine size and high surface-to-volume ratio. Strong SHG signal has been observed from silver nanoparticles dispersed in aqueous colloidal solution, in which the SHG signal is enhanced due to a resonance with the localized surface plasmon of silver nanoparticles. Further experiments proved that the SHG signal predominantly originates from the particle surface, in full agreement with the intrinsically interface-sensitive properties of SHG. With the surface origin of the signal now well established, SHG can be used to probe the adsorption and reactions of thiol molecules at the nanoparticle surface in situ and in real time. It is experimentally demonstrated that the free energy change, activation energy, as well as adsorption density of the reactions of a variety of neutral and anionic thiols at the particle surface can be measured by means of SHG. The reaction mechanisms at the molecular level have been deduced, and the neutral vs anionic thiols are found to exhibit qualitatively different reaction mechanisms that reflect the effect of their molecular interactions with the particle surface. Oligoacenes, such as pentacene and hexacene, constitute a family of organic semiconductors that exhibit remarkable optoelectronic properties. In contrast to the nanoparticles in which surface interactions are dominant, as the sizes of materials become larger, the bulk characteristics become more deterministic. Therefore, polarized linear absorption and transient absorption spectroscopies have been applied to study the excitonic properties of crystalline pentacene and the mechanism of singlet fission in crystalline hexacene, respectively. The polarized absorption spectra of crystalline pentacene have been obtained by measuring transmitted light normal to the ab herringbone plane of micro-sized ultrathin single crystals. The significant deviations between the spectral line shapes polarized along the b-axis and orthogonal to the b-axis provide detailed information on the anisotropic mixing nature of the Frenkel/charge-transfer excitons responsible for the pronounced Davydov splitting between the lowest-energy singlet states. Additionally, both singlet and triplet Davydov splittings were also observed from the linear and transient absorption experiments in micrometer-sized ultrathin hexacene single crystals. A two-step process of anisotropic singlet fission was uncovered from the kinetic data, in which singlet fission at different rates were deduced along the a- and b-axes. Both the spectral and kinetic features indicate that singlet fission in crystalline hexacene is an anisotropic and charge-transfer mediated many-molecule process. / Chemistry

Ionically self-assembled monolayer (ISAM) films are typically an assemblage of oppositely charged polymers built layer by layer through Coulombic attraction utilizing an environmentally friendly process to form ordered structures that are uniform, molecularly smooth and physically robust. ISAM films have been shown to be capable of the noncentrosymmetric order requisite for a second-order nonlinear optical response with excellent temporal and thermal stability. However, such films fabricated with a nonlinear optical (NLO) polyanion result in significant cancellation of the chromophore orientations. This cancellation occurs by two mechanisms: competitive orientation due to the ionic bonding of the polymer chromophore with the subsequent polycation layer, and random orientation of the chromophores within the bulk of each polyanion layer. A reduction in film thickness accompanied by an increase in net polar ordering is one possible avenue to obtain the second-order susceptibility chi(2) necessary for practical application in electro-optic devices. In this thesis, we discuss the structural characteristics of ISAM films and explore a novel approach to obtain the desired characteristics for nonlinear optical response. This approach involves a hybrid covalent / ionic self-assembly technique which affords improved net dipole alignment and concentration of monomer chromophores in the film. This technique yields a substantial increase in chi(2) due to the preferential chromophore orientation being locked in place by a covalent bond to the preceding polycation layer. The films fabricated in this manner yield a chi(2) that substantially exceeds that of any known polymer-polymer ISAM film. This covalent-hybrid ionically self-assembled multilayer (CHISAM) technique is demonstrated to result in films suitable for electro-optic devices, with measured electro-optic coefficient (14 pm/V) comparable to that of the inorganic crystal lithium niobate (30 pm/V). Thermal and temporal stability are important properties of electro-optic device implementation, and are demonstrated for CHISAM films. CHISAM films have remained stable at room temperature for more than 420 days, and suffered no loss of chi(2) when held at 80 C for 36 hours, followed by 150 C for 24 hours. Studies are also presented that demonstrate the ability to produce ISAM chi(2) films that are nearly one micron thick, and exhibit no evidence of a thickness limitation to the polar order. Analytical considerations for second-order NLO characterization of thick films are addressed in detail. The effect of absorption of the second harmonic wavelength and resonant enhancement of chi(2) are investigated, and it is demonstrated that accurate determination of chi(2) may be made for thick films and for films that absorb the second harmonic. The temporal and thermal stability of a variety of ISAM and CHISAM NLO films are examined in detail. In some cases, a decrease in the NLO response is observed at elevated temperature that is completely restored upon cooling. Studies are presented that suggest this effect is a result of thermally induced trans-to-cis isomerization of azo linkages in the NLO chromophores. / Ph. D.

Ionically self-assembled monolayer (ISAM) films are typically an assemblage of oppositely charged polymers built layer by layer through coulombic attraction utilizing an environmentally friendly process to form ordered structures that are uniform, molecularly smooth, and physically robust. ISAM films have been shown to be capable of the noncentrosymmetric order requisite for a second-order nonlinear optical response. However, films fabricated with a nonlinear optical (NLO) polymer result in significant cancellation of the chromophore orientations. This cancellation occurs by two mechanisms: competitive orientation due to the ionic bonding of the polymer chromophore with the subsequent polycation layer, and random orientation of the chromophores within the bulk of each polyanion layer. A reduction in film thickness accompanied by an increase in net polar ordering is one possible avenue to obtain the second-order nonlinear optical susceptibility chi(2) necessary for electro-optic devices. In this thesis, we will discuss the structural characteristics of ISAM films and explore three novel approaches to obtain the desired characteristics for nonlinear optical response. One approach involves the variation of solution parameters of several different cationic polymers separately from the polyanion solution in order to reduce the competitive chromophore orientation at the layer interfaces and to reduce the thickness of the inactive polycation layer. We have found that the complexity of ISAM films does not allow large chi(2) values in polyion-based films, and that the selection of the polymer cation is vital to achieve second harmonic generation (SHG) at all. The second approach involves the incorporation of dianionic molecules into ISAM films in order to eliminate both competitive chromophore orientation and random chromophore orientation inherent with polymer chromophores. We have also studied the effects of complexing dianionic chromophores with beta-cyclodextrin in order to increase solubility and improve chromophore orientation. This approach fails because the outermost monolayer of dianionic chromophore is only tethered to the preceding polycation layer by a single ionic bond for each molecule, so each chromophore can by dissociated during the following immersion into the cation solution. Finally, we have introduced a novel approach of hybrid covalent / ionic self-assembly which overcomes these disadvantages and yields a substantial increase in chi(2) due to the chromophore being locked in place to the preceding polycation layer by a covalent bond. The films fabricated in this manner yield a chi(2) that rival any polymer-polymer films despite the very low first-order molecular hyperpolarizability beta of the incorporated monomer. This suggests that incorporation of high beta molecules may result in significant improvement of chi(2), holding high promise for the hybrid covalent / ionic self-assembly technique. / Master of Science

Detailed studies are presented of thin films containing a polycation, a nonlinear optically (NLO) active chromophore, and a synthetic hectorite that self-assemble into the noncentrosymmetric structure required for second order nonlinear optical responses. UV/Vis spectroscopy and ellipsometry were used as probes to monitor film growth for upto 25 deposition cycles. Exceptionally homogeneous films were obtained with regular film growth for up to the 25 cycles deposited. ISAM films self-assemble from polyelectrolyte solutions due to coulombic interactions between a charged substrate and the charged polymer in solution. Charges accumulating at the surface restrict further growth due to charge overcompensation at the surface. The entire process occurs relatively quickly as compared to other competing assembly techniques such as Langmuir-Blodgett assembly and covalent self-assembly. Previous studies indicated that second harmonic signal diminishes after the deposition of the first few bilayers. This is potentially due to adjacent layer interpenetration, which becomes prominent moving further away from the hard substrate interface. Laponite RD, a synthetic hectorite was introduced in the films in an effort to minimize interpenetration of adjacent bilayers and hence maintain chromophore orientation in every bilayer of the ISAM film. The film was deposited in quadlayers that have the following sequence: Polycation–Laponite–Polycation–Chromophore. This study is unique in its approach as it investigates the possible implications of film interpenetration on the NLO-activity of ISAM films that can be easily fabricated. It also shows the effects of different interfaces on the NLO-activities of the films. We have investigated the effect of changing the polycation from poly(allylamine hydrochloride) (PAH) and poly(diallyldimethylammonium chloride) (PDDA) and the solution pH to see how these variables affect the growth and NLO properties of ISAM films. At lower pH values (specify relevant range of values), for both polycations, intrachain and interchain repulsion is strong due to little electrostatic screening. This results in polycation deposition in relatively thin, train-like layers. At higher pH levels (specify relevant range of values here) the electrostatic screening is greater due to a higher effective ionic strength. At these conditions, intrachain and interchain repulsion is reduced and so the polymers adsorb to form thicker layers with more loops and tails than for the case at lower pH. This also results in a higher density of the chromophore in the film. Extremely smooth surfaces of Laponite RD in film were obtained as confirmed by AFM imaging on glass. Regular quadlayer growth monitored by UV/Vis spectroscopy and ellipsometry was observed for up to 25 quadlayers. Second harmonic generation (SHG) signal was not conclusively affected by the presence of laponite as the decrease of signal was seen after the first few layers in the laponite containing films. This decrease was however was not as sharp in the films containing laponite as in the films that did not contain laponite. It was also noted that the SHG was not so much affected by the number of layers deposited but more so by the distance of the chromophore layer from the hard glass interface. This study thus brings to light the very important effect of the glass interface on the NLO-activity of these films. / Master of Science

With a growing demand in industry for cost effective, increased data handling capabilities great attention has been paid to the study of various polymer systems for use in optical telecommunications. Inorganic crystals, currently used in such systems, have high performance, but are more expensive and less obtainable than organic materials. Recent advances in techniques for developing highly efficient and inexpensive organic polymeric electro-optic (EO) devices compatible with current state-of-the-art electronics have created an interest in the commercialization of such electro-optic devices. In light of the many advantages of utilizing organic materials for electro-optic applications, numerous methods have been developed to produce nonlinear optically (NLO)-active polymeric films for such purposes. Ionic self-assembled multilayer (ISAM) films are a recently developed class of materials that allows detailed structural and thickness control at the molecular level, combined with ease of manufacturing and low cost. However, the layer-by-layer deposition technique utilized for this method currently requires lengthy processing times that challenge the feasibility of fabricating a thick film suitable for EO modulator device fabrication. This study focuses on addressing the influence of several pertinent processing variables affecting these challenges for application to electro-optic device fabrication. This study investigated (1) the effect of forced convection, varying deposition time and varying dye concentration on the properties of PAH/Procion Brown films fabricated via the hybrid reactive deposition scheme, (2) the automation and optimization of the fabrication of thick NLO active films and (3) the use of the hybrid covalent-electrostatic deposition scheme to fabricate a polymeric waveguide device with an electro-optic coefficient comparable to that of lithium niobate (LiNbO₃). At fixed deposition time and concentration conditions, the presence of convection had little demonstrated effect on films with deposition times shorter than 2 minutes. For the 5 minute case, the presence of convection correlated with a ~45% increase in Ï (2)zzz values values and a 25% increase in absorbance per bilayer. At a constant dye concentration of 5 mg/ml, the deposition time had little effect on SHG for deposition times less than two minutes. In the presence of convection, the increase in deposition time from 2 minutes to 5 minutes showed a 57% increase in Ï (2)zzz values and a 30% increase in absorbance per bilayer. For a deposition time of 2 minutes in the presence of convection, the dye solution concentration was successfully reduced 5-fold (from 5 mg/ml to 1 mg/ml) with less than a 5% difference in Ï (2)zzz values, less than a 15% decrease in absorbance per bilayer and no detriment to film quality. These results strongly indicate that the deposition conditions remain well outside of the transport-limited regime at a dye concentration of 1 mg/ml. Rather, the surface reaction rate apparently is controlling. Depositing slides at an elevated temperature (~35°C), had an undetermined effect on Ï (2)zzz values, but showed a 15% increase in absorbance per bilayer. An automatic dipper was programmed to replicate the current manual deposition method to fabricate a film suitable for EO modulator devices. Utilizing the optimal conditions for the processing variables, an optically-homogeneous, 100 nm-thick film was fabricated utilizing the automated process, yielding a Ï (2)zzz values~ 23 x 10⁻⁹ esu. A three-layer coplanar electro-optic device was fabricated utilizing the hybrid reactive deposition method. For this device, the presence of added salt was found to increase the electro-optic coefficient r33 by a factor of 3 compared to its value when made with no added salt. The electro-optic coefficient of the added salt case was found to be about 1/2 that of lithium niobate (LiNbO3). / Master of Science

Owing to its centrosymmetric structure, the critical optical component of a silica fiber cannot to possess a second-order nonlinear optical susceptibility, Χ(²), preventing a silica fiber from many potential applications. Here, we theoretically and experimentally demonstrate a new technique to generate large and thermodynamically stable second-order nonlinearity into silica optical tapered fibers without breaking the centrosymmetry of the silica glass. The nonlinearity is introduced by surface layers with high polar-ordering fabricated by a novel hybrid covalent/ionic self-assembly multilayer technique. Despite the overall rotational symmetry of the nonlinear fiber, we observe significant second harmonic generation with ~ 400–500 fold enhancement of the SHG power compared to the traditional tapers. Phase matching for a SHG process in second-order nonlinear tapered fibers is also realized by the compensation of waveguide modal dispersion with material chromatic dispersion, which occurs only for submicron tapers where the modal dispersion is large. In addition, quasi-phase-matching for a nonlinear taper can be accomplished by introducing a periodic pattern into the nonlinear film coating. We use UV laser ablation for the controlled removal of particular nonlinear film segments on a taper surface in order to produce a Χ(²) grating structure. A resulting SHG enhancement from quasi-phase-matching is observed over a broadband spectrum of the pump light mainly due to the non-uniform shape of a taper waveguide. The laser ablation is a clean and fast technique able to produce well-define patterns of polymer films on either flat or curved substrate geometry. With surface layers containing reactive functional groups e.g. primary amines, we demonstrate that the resulting patterned film obtained from the laser ablation can be used as a template for further self-assembly of nanoparticles with high selectivity. A pattern feature size down to ~ 2μm or smaller can be fabricated using this approach. We also discuss preliminary results on a novel technique to further improve spatial accuracy for selective self-assembly of nanoparticles at an unprecedented level. Different types of nanoparticles are joined in order to form well-defined, molecular-like superstructures with nanoscale accuracy and precision. The technique is based on a selective surface functionalization of photosensitive molecules coated on metallic nanoparticles utilizing enhanced two-photon photocleavage at the plasmonically-active sites (hot spots) of the nanoparticles in resonance with an applied electromagnetic wave. As a result, the surface functional groups at the nanoparticle hot spots are different from the the other areas, allowing other kinds of nanoparticles to self-assemble at the hot spots with high degree of selectivity. / Ph. D.

It is of paramount importance to our society that the environment, life style, science and amusement flourish together in a balanced way. Some trends in this direction are the increased utilization of renewable energy, like solar photovoltaics; better health care products, for example advanced biosensors; high definition TV or high resolution cameras; and novel scientific tools for better understanding of scientific observations. Advancement of micro and nanotechnologies has directly and positively impacted our stance in these application domains; one example is that of vertical periodic or aperiodic nano or micro pillar assemblies which have attracted significant research and industrial interest in recent years. In particular, Si pillars are very attractive due to the versatility of silicon. There are many potential applications of Si nanopillar/nanowire assemblies ranging from light emission, solar cells, antireflection, sensing and nonlinear optical effects. Compared to bulk, Si pillars or their assemblies have several unique properties, such as high surface to volume ratios, light localization, efficient light guiding, better light absorption, selective band of light propagation etc.      The focus of the thesis is on the fabrication of Si pillar assemblies and hierarchical ZnO nanowires on Si micro structures in top-down and bottom-up approaches and their optical properties and different applications. Here, we have investigated periodic and aperiodic Si nano and micro structure assemblies and their properties, such as light propagation, localization, and selective guiding and light-matter interaction. These properties are exploited in a few important optoelectronic/photonic applications, such as optical biosensors, broad-band anti-reflection, radial-junction solar cells, second harmonic generation and color filters.         We achieved a low average reflectivity of ~ 2.5 % with the periodic Si micropyramid-ZnO NWs hierarchical arrays. Tenfold enhancement in Raman intensity is also observed in these structures compared to planar Si. These Si microstructure-ZnO NW hierarchical structures can enhance the performance and versatility of photovoltaic devices and optical sensors. A convenient top-down fabrication of radial junction nanopillar solar cell using spin-on doping and rapid thermal annealing process is presented. Broad band suppressed reflection, on average 5%, in 300- 850 nm wavelength range and an un-optimized cell efficiency of 6.2 % are achieved. Our method can lead to a simple and low cost process for high efficiency radial junction nanopillar solar cell fabrication.            Silicon dioxide (SiO2) coated silicon nanopillar (NP) arrays are demonstrated for surface sensitive optical biosensing. Bovine serum albumin (BSA)/anti-BSA model system is used for biosensing trials by photo-spectrometry in reflection mode. Best sensitivity in terms of limit of detection of 5.2 ng/ml is determined for our nanopillar biosensor. These results are promising for surface sensitive biosensors and the technology allows integration in the CMOS platform.         Si pillar arrays used for surface second harmonic generation (SHG) experiments are shown to have a strong dependence of the SHG intensity on the pillar geometry. The surface SHG can be suitable for nonlinear silicon photonics, surface/interface studies and optical sensing.         Aperiodic Si nanopillar assemblies in PDMS matrix are demonstrated for efficient color filtering in transmission mode. These assemblies are designed using the ‘‘molecular dynamics-collision between hard sphere’’ algorithm. The designed structure is modeled in a 3D finite difference time domain (FDTD) simulation tool for optimization of color filtering properties. Transverse localization effect of light in our nanopillar color filter structures is investigated theoretically and the results are very promising to achieve image sensors with high pixel densities (~1 µm) and low crosstalk. The developed color filter is applicable as a stand-alone filter for visible color in its present form and can be adapted for displays, imaging, smart windows and aesthetic applications. / <p>QC 20160407</p>