The plasmon hybridization method is a powerful approach for calculating the energies of plasmon resonances in composite nanostructures. It is shown that the plasmons of a complex nanostructure can be viewed as resulting from hybridization of the elementary plasmon modes associated with the different surfaces of the nanostructure. This interaction leads to the formation of bonding and anti-bonding plasmon modes. The picture is entirely analogous to the interaction of electronic levels in molecular orbital theory. We present an application to spherical nanoparticles such as metallic nanoshells and concentric nanoshells (nanomatrushkas), nanoparticle dimers, and nanoparticles interacting with metallic surfaces.

The 'chemical mechanism' of surface enhanced Raman scattering (SERS) is investigated by quantum mechanical methods for pyridine adsorbed onto a copper cluster. Gaussian orbital based density functional theory with a B3LYP exchange-correlation functional is used to calculate the ground state structure and normal coordinates of the molecule-surface complex system, and the sum-over-states method, which uses excited state energies and dipole matrix elements from CIS (singles CI) calculations and the INDO/S semi-empirical method, is used to calculate the zero and non-zero frequency dependent polarizability derivatives that determine the Raman intensities. The cluster in these calculations is a copper tetramer whose excited state widths have been broadened to mimic interaction with bulk metal. The present method succeeds in describing the Raman spectrum of the adsorbed pyridine molecule, including changes in the spectrum that arise from adsorption on the surface, and differences between the zero frequency and finite frequency spectra. However the model is still quite primitive in its evaluation of the SERS enhancement factor.

Anderson localization in random potential fields has been studied extensively for the last fifty years. It is commonly accepted that in 1D and 2D systems characterized by non-correlated random potential distributions, all states are exponentially localized. In this paper we investigate the eigen-problem for Surface Plasmons (SP) in random metal-dielectric films. We show that short-range correlations presented in the governing Kirchhoff's Hamiltonian (KH) result in delocalization of the eigenstates at the band center. The delocalization is shown to be manifested through power law singularities for the density of states and SP localization lengths. The study of the system size dependence of the nearest neighbor's level spacing distributions shows a gradual shift of the SP eigen-problem from a metallic phase for small system sizes into an insulating quantum phase for infinite systems. It reveals a genuine metal-insulator transition that takes place in the composite and is characterized by quantum percolation threshold P_q which is higher than the corresponding geometrical critical concentration P_c.

The local electric field enhancements around various nanoshell structures are investigated using the Finite Difference Time Domain (FDTD) method. The method provides a convenient and systematic approach for calculating several physical properties of nanostructures, including the optical absorption and scattering cross sections as well as the local electromagnetic fields. The method is applied to single uniform nanoshells as well as nanoshells with surface defects and structural distortions. The results show that, while defects can significantly affect local electric field enhancements, far field results such as extinction spectra can be remarkably insensitive to defects and distortions.

In nanooptics, we theoretically predict a possibility with high efficiency to deliver electromagnetic energy to and concentrate it on the nanoscale. It is achieved by converting light waves to surface plasmon polaritons (SPP's) and slowly (adiabatically) varying in space dielectric (semiconductor) environment of a metal surface to gradually slow down and completely stop SPP's, converting them to surface plasmons localized on the nanoscale. Though adiabatic, this transformation should be as rapid as possible to minimize the absorption losses in the metal. Another way is to launch SPP's to propagate toward the tip of a tapered plasmonic waveguide. The SPP's are slowed down and asymptotically stopped when they tend to the tip, never actually reaching it (the travel time to the tip is logarithmically divergent). The rapid adiabatic stopping of SPP's causes accumulation of energy and giant local fields at the stopping point. There are multiple applications possible of these phenomena in nanooptics, nanoprobing, and nanomodification.

The detailed theoretical analysis of the fine optical phenomena caused by surface plasmon polariton (SPP) excitation in a metallic film with weakly modulated dielectric permittivity is made for both symmetrical and nonsymmetrical dielectric arrangements. SPP modes in the film are close to those existing at an interface between metal and dielectric half spaces (these polaritons are weakly coupled under the symmetrical surrounding), and the effect of enhanced light transmission (ELT) caused by photon-SPP-photon transformations can occur. The advantage of the approach used is that we present the most interesting results in a simple analytical form. The dispersion relation for the film SPP for both arrangements is investigated. On this basis the comprehensive examination of the ELT effect is performed. The parameters of the problem (optimal film thickness, optimal modulation amplitude) responsible for total suppression of the zeroth- and/or nonzeroth-order reflected waves and maximal transmission are found. The results are of essential interest for optical nano-devices design.

The use of virus nanoparticles, specifically Chilo and Wiseana Iridovirus, as core substrates in the fabrication of metallodielectric, plasmonic nanostructures is discussed. A gold shell is assembled around the viral core by attaching small, 2 - 5 nm, gold nanoparticles to the virus surface by means of inherent chemical functionality found within the protein cage structure of the viral capsid. These gold nanoparticles act as nucleation sites for electroless deposition of gold ions from solution. The density of the gold nucleation sites on the virus was maximized by reducing the repulsive forces between the gold particles, which was accompolished by controlling the ionic strength of the nanoparticle solution. UV/Vis spectroscopy and transmission electron microscopy were used to verify creation of the virus-Au particles. The optical extinction spectra of the metallo-viral complex were compared to Mie scattering theory and found to be in quantitative agreement.

We report on near-field Raman spectra of a single nanocrystal of adenine molecules using a silver-coated apertureless probe tip. Raman signal is amplified due to surface plasmon polaritons localized at the metallic tip by a factor of more than 2700 times compared with the far-field Raman signal. Plasmonic near-field Raman spectrum showed eight Raman bands assigned to the normal modes of adenine molecule based on the density functional theory calculations. Vibrational frequencies of some Raman bands are observed to have shifted to the values of the corresponding bands, observed using conventional surface enhanced Raman-scattering spectrum. We found that these frequency shifts are caused by the transient states of the adenine-silver complexes by analyzing vibration mode of the complexes; that is, the near-field Raman spectra of adenine agree with Raman spectra of the complexes which are calculated by reducing the bond distance between an adenine molecule and a silver atom. Repulsive forces calculated from reduction of the bond distance were equal to the atomic force applied to the adenine molecule in our Raman NSOM experiment. All results support that the active Raman shift occurs owing to the deformation of adenine molecules pressurized by the silver atoms of the tip.

We present an alternative approach to optical probes that will ultimately allow us to measure chemical concentrations in microenvironments within cells and tissues. This approach is based on monitoring the surface-enhanced Raman scattering (SERS) response of functionalized metal nanoparticles (50-100 nm in diameter). SERS allows for the sensitive detection of changes in the state of chemical groups attached to individual nanoparticles and small clusters. Here, we present the development of a nanoscale pH meter. The pH response of these nanoprobes is tested in a cell-free medium, measuring the pH of the solution immediately surrounding the nanoparticles. Heterogeneities in the SERS signal, which can result from the formation of small nanoparticle clusters, are characterized using SERS correlation spectroscopy and single particle/cluster SERS spectroscopy. The response of the nanoscale pH meters is tested under a wide range of conditions to approach the complex environment encountered inside living cells and to optimize probe performance.

As an efficient nanolens, we propose a self-similar linear chain of several metal nanospheres with progressively decreasing sizes and separations. To describe such systems, we develop the multipole spectral expansion method. Optically excited, such a nanolens develops the nanofocus (``hottest spot'') in the gap between the smallest nanospheres, where the local fields are enhanced by orders of magnitude due to multiplicative, cascade effect of its geometry and high $Q$-factor of surface plasmon resonance. The spectral maximum of the enhancement is in the near-ultraviolet, shifting toward the red as the separation between the spheres decreases. We also introduce surface plasmon amplification by stimulated emission of radiation (spaser) in nanolenses. Predominantly amplified are the dark, odd-parity eigenmodes, which do not suffer dipole-radiative losses and produce coherent, local optical fields comparable in strength to atomic fields, with minimal far-field radiation. The proposed systems can be used for nanooptical detection, Raman characterization, nonlinear spectroscopy, nano-manipulation of single molecules or nanoparticles, and other applications.

We employed micro-electro-mechanical system (MEMS) techniques to fabricate parallel sub-wavelength thin-wire structures of metals on elastomeric matrices. From the transmission measurement by Fourier Transform Infrared Spectroscopy, we observed the depressed plasma frequencies of these thin-wire structures at terahertz (THz) ranges. Furthermore, the behavior of depressed plasma frequencies is very sensitive to the polarization of the applied field. The reasons that these engineered materials exhibit unprecedented properties not observed in nature can be interpreted by two factors: the diluted electron densities and the enhancement of electron mass. In addition, the plasma frequencies are readily tunable over a broad frequency range by extending the elastomeric matrices to change their periodicity. These novel properties of tunable and polarization-dependant plasma frequencies at THz ranges promise abundant striking applications in THz optics.

Recent interest in the study of metal nanoparticles and related structures has greatly increased. Technologies such as electron beam lithography facilitate the fabrication of such subwavelength structures. Much research has focused on the linear optical properties of high-symmetry particles, such as ellipsoids and spheroids. However, we focus on both the linear and nonlinear optical responses of low-symmetry L-shaped nanoparticles. We show that these nanoparticle arrays are exceptionally sensitive to polarization. Small asymmetries in the particle shapes lead to large deviations in the primary extinction directions from expected locations. The structural asymmetries may also induce optical activity. We present results of detailed polarization analysis through second-harmonic generation experiments that are based on symmetry arguments regarding the second-order susceptibility tensor. The results confirm that the structural deviations from the ideal shape lead to further breakdown in the symmetry properties of the arrays.

Optical properties of the modern kinds of nano/microstructure materials - nuclear microfilters (NM) and their metallic replica (so called "needle structures" (NS)) are studied in visible as well as in IR region. The materials are produced from PolyEthylene Terephtalate (PET) film irradiated by accelerated Xe ions as well as by actinoids. The transparence of the ion-irradiated PET films decreases and the reflection increases with the duration of chemical treatment. The interference fringe pattern (IFP) becomes diffuse and weak at the final stages of the etching process. An intense diffraction background (DB) appears in the IR-spectra. A correlation between IFP and DB change and evoked by micropore formation the PET film mass losses is established. DB spectral form can be described by ~λ-2 law at initial stages of the etching and by standard Raleigh law (~λ-4) at the end of the process. The optical properties of the NS prepared from copper and nickel on the base of the same NM are investigated. In both cases development of the surface roughness results in suppression of the "mirror-like" component in the reflected light. A phenomenon of the surface-enhanced IR scattering is discovered for Cu-NS. Possible applications of such nano/microstructure materials in optics are discussed.