The nanosphere lithography (NSL) technique is used to make periodic gold array of prismatic nanoparticles. We use the femtosecond time resolved double beam transient optical detection to determine the coherent lattice oscillation in gold nanoparticles. Coherent lattice oscillation is compared on gold nanoparticles of different sizes and shapes. The effect of changing shape on the oscillation period was studied. Different environmental effects on the coherent lattice oscillation are eliminated by measuring the oscillation of the prismatic shape before and after we anneal it to spherical shape of the same number of atoms. A large change in the oscillation period is observed which agrees with the calculated period using different equations for the corresponding shapes.

Up to fifty fold increases in water soluble conjugated phenylenevinylene polymer fluorescence are observed when these polymers are adsorbed onto silver nanoparticle treated surfaces with layer-by-layer deposited polyelectrolyte spacers. The silver particle density and spacer thickness dependence of the enhancement are investigated. Using absorption, fluorescence, fluorescence excitation and transient photoluminescence measurments, we infer the relative importance of absorption and emissive rate increases in explaining the observed enhancement. Large blue shifts due to interactions of the molecular excited states with the silver particle plasmons are observed.

We study enhancement of fluorescence of molecular species bound within metallic nanocavities. An electromangetic model of dipole radiation within a nanocavity shows an increase in radiative output consistent with experimental yield estimates and also verifies the strong fluorescence isolation from species lying outside the nanocavity.

Tip-enhanced Raman spectroscopy (TERS) is emerging as a promising spectroscopic tool for nanoscale characterization of chemical composition, structure, stresses and conformational states. However, its widespread application requires optimization of the technique to reproducibly achieve sufficiently high contrast between near-field and far-field signals. We present a TERS spectrometer, based on side illumination geometry, which demonstrates reproducible enhancements of the Raman signal of the order of 10³-10⁴ for a variety of molecular, polymeric and semi-conducting samples using both silver- and gold-coated tips. We estimate the localization of the Raman signal enhancement to be ~20 nm. For thick samples, the contrast is limited by a strong far-field signal (from the laser illuminated spot) that overpowers the near-field signal (enhanced in the vicinity of the tip). Optimizing the polarization geometry and the incident angle, we have achieved a contrast between near-field and far-field signal of 12 times on (100) Si - a level that makes this technique attractive for characterization of silicon nanostructures.

While much work has focused on simulation and measurement of plasmon resonances in noble metal nanostructures, usually the simulation tool is used as a confirmation of experimental results. In this work we use a finite difference time domain (FDTD) technique to calculate the plasmon resonance and electric field enhancement of Ag nanoparticles in regular arrays on quartz substrates. Such structures have also been prepared by e-beam lithography, and the plasmon resonance and surface-enhanced Raman scattering strength of arrays with different nanoparticle size and spacing have been investigated. Arrays of cylindrical nanoparticles were fabricated with varying particle size and interparticle spacing. The observed extinction peaks agree very well with the extinction peaks as calculated by FDTD; typically within a few percent. Experimental plasmon peak widths are considerably larger than their ideal values due to inhomogeneous broadening. As expected, the particle array with highest SERS enhancement has its plasmon resonance nearest the laser and Stokes-shifted wavelengths. We believe the FDTD modeling tool is accurate enough to use as a predictive tool for engineering plasmonic nanostructures.

We present a microscopic model for surface-enhanced Raman scattering (SERS) from molecules adsorbed on small noble-metal nanoparticles. We demonstrate that, in nanometer-sized particles, SERS is determined by a competition between two distinct quantum-size effects: Landau damping of surface plasmon resonance and reduced screening near nanoparticle surface. The first mechanism comes from the discreteness of energy spectrum in a nanoparticle and leads to a general decrease in SERS. The second mechanism originates from the different effect of confining potential on sp-band and d-band electron states and leads to a relative increase in SERS. We calculate numerically the spatial distribution of local field near the surface and the enhancement factor for different nanoparticles sizes.

The thylakoid membranes isolated from spinach chloroplasts were immobilized on a flat gold film and a gold film having 600 nm nanowells in the absence or presence of 20 nm gold colloids. The immobilized thylakoids showed photosynthetic properties upon surface plasmon (SP) enhanced excitation. The localization of SP field by the randomly distributed gold nanowells was confirmed by the specific light scattering and transmission properties. The thylakoids immobilized in/over the gold nanowells showed specific fluorescence spectrum suggesting the excitation of chlorophylls by the localized SP field in/around the nanowells.

To realize a nanometer-scale optical waveguide for far-/near-field conversion, we proposed a nanodot coupler which is the linear array of closely spaced metallic nanoprticles in order to transmit the optical signal to a nanophotonic device. In comparison with metallic core waveguide, the use of nano-dot coupler is expected to realize lower energy loss due to the resonant in the metallic nanoparticles. First, to optimize the efficiency in the nanodot coupler, we checked whether the single Au nanoparticles led to efficient scattering. The Au nanoparticles on the glass substrate were fabricated by the focused ion beam milling technique. The optical near-field intensity for the Au nanoparticles in diameter range from 100 to 300nm with constant height of 50nm were observed by the collection mode near-field optical microscope (NOM) at λ = 785nm. Near-field intensity took the maximum for the Au nanoparticle with 200nm in diameter, and this result is in good agreement with the calculated value of plasmon resonance by Mie's theory for an Au prolate spheroid. Next, we examined the plasmon-polariton transfer of nanodot couplers whose diameter range from 150 to 300nm by the collection mode NOM. The efficient energy transfer was observed only in the nanodot coupler with 200nm in diameter. This result agreed well with that of single Au nanoparticles. From these results, efficient energy transfer along nanodot coupler was confirmed by the near-field coupling between plasmon-polariton in the nanoparticles.

Considerable attention is devoted to determining and refining the optical properties of metal nanoparticle arrays. The evolution of nanofabrication techniques towards miniaturizing optoelectronic devices naturally suggests the possibility of using such arrays in nanoscale optical components. However, small-scale defects (tens of nanometers or less) in individual particles themselves may exert a significant influence on the overall optical responses of the array, especially when the particles (and/or arrays) appear symmetric on the scale of the particle (and/or array). We have observed strong linear and nonlinear chiral responses from regular arrays of lithographically-designed, low-symmetry, L-shaped gold nanoparticles (~ 200 nm arm lengths) through polarization azimuth rotation and circular difference measurements. Second-harmonic generation measurements exhibit much larger circular difference responses, being more sensitive to symmetry. Comparisons between arrays of symmetric and asymmetric particles imply that the small defects may be the primary source of broken symmetry and hence chirality.

The sensitivity of surface plasmon band location in noble metal nanoparticles to the refractive index, n, of the medium is investigated using closed form approximations to the particle polarizability. Within its range of validity, quasi-static analysis indicates that single component nanoparticles, including hollow nanoshells, have peak wavelength sensitivities that are determined exclusively by band location and dielectric 'constants' of the metal, ε, and medium, n². Among particle plasmons that peak in the frequency range where the real part of the metal dielectric function varies linearly with wavelength and the imaginary part is small and slowly varying, the sensitivity of the peak wavelength, λ*, to refractive index, n, is found to be a linearly increasing function of λ*, regardless of the structural features of the particle that determine λ*. The dependence of the sensitivity on band position is determined by the wavelength dependence of the real part of the particle dielectric function. The results are applicable to all particle shapes, including rods, disks, hexagons, chopped tetrahedra, and hollow nanoshells and are not limited to dipolar resonances. Modification of the quasi-static analysis to account for electrodynamic effects to second order in the size parameter indicates that the structural independence of the refractive index sensitivity extends to larger nanoparticles than those accurately represented by quasi-static theory. The bulk refractive index sensitivity yielded by the theory serves as an upper bound to sensitivities of nanoparticles on dielectric substrates and sensitivities of nanoparticles to local refractive index changes, such as those associated with biomolecule sensing.

We report a 2-dimensional surface plasmon resonance (SPR) imaging array sensor based on differential phase measurement between p- and s-polarization. This parallel detection provides the advantage of high-throughput sensing, which is essential in recent biosensing technology. In the differential measurement approach, the signal (p) and reference (s) beams go through exactly identical optical path. This greatly improves the phase detection stability. In the present setup we use a low-cost imaging device and a simple data analysis program to perform the required arrayed sensing operation. The system demonstrates a refractive index resolution of 1x10^-4 RIU per degree phase change.

We study localized-surface plasmon resonance (LSPR) and the surface-enhanced Raman scattering (SERS) gain of gold cylindrical and ellipsoidal nanorods of different diameter or major axis. The LSPR and SERS gains are calculated with the three dimensional Finite-Difference Time-Domain method using Drude-Lorentz dispersion model. We find that the maxima of the extinction spectrum and the average SERS gain of each investigated nanostructures are shifted whatever their size and their shape.

Realistic finite-difference time-domain simulations are carried to learn how to understand and control localized surface plasmons (LSP's) and traveling surface plasmon polaritons (SPP's) in metallic nanostructures. We show how to control the spatio-temporal behavior of LSP hot spots in cone-shaped metal nanoparticles. We discuss how to intensify and lengthen SPP's in thin metallic films. Finally, we discuss the relative roles of LSP's and SPP's in thin metal films with nanoscale holes and slits.

The strongly localized quasi-static eigenstates (also known as surface-plasmon resonances) which are found in a small nanometric cluster of spherical inclusions can form the basis for some interesting potential applications such as SPASER and nanolens. In a SPASER, a strong coherent electric field, oscillating at a frequency ω in the visible or infra-red spectral range, can be excited in a spatial region whose linear dimensions are much smaller than the wavelength appropriate to that frequency. In a nanolens an incident electromagnetic field, oscillating at such a frequency, can be focused to a spot whose size is much less than the relevant wavelength. An important property of such resonances is their finite radiative lifetime, which is infinite in the strict quasi-static limit. One needs to solve the full Maxwell's equations in order to find the radiative decay rate, and consequently the lifetime, of such an eigenstate. We develop a method for calculating such lifetimes for clusters of closely spaced spherical inclusions. We also discuss how symmetry properties of such a cluster can be exploited to ensure that certain eigenstates have especially long radiative lifetimes.

The local electric field enhancement in the vicinity of a metal-coated or metal tip is a significant factor in the performance of apertureless near-field optical microscopy and spectroscopy techniques. Enhancement, which is related to the generation of localized surface plasmons in the metal tip, can be maximized when the plasmons resonate at the probing wavelength. Thus the resonance frequencies of the tip apex are crucial to near-field optics. However, it remains a challenge to measure the optical properties of the apex of a tip with a radius much smaller than the wavelength of light. A dark-field scattering spectroscopy method is presented in combination with a side-illumination nano-Raman spectrometer to experimentally determine the optical properties of the tip. The dependence of the optical resonance on the metal deposited is shown for silver- and gold-coated tungsten tips as well as gold-coated silicon nitride tips. The enhancement for Si using gold-coated silicon nitride tips is somewhat larger for a wavelength of 647 nm than for a wavelength of 514.5 nm. The former is closer to the plasmon resonance observed for this tip at ~680 nm.

Several classes of computational methods are available for computer simulation of electromagnetic wave propagation and scattering at optical frequencies: Discrete Dipole Approximation, the T-matrix - Extended Boundary Condition methods, the Multiple Multipole Method, Finite Difference (FD) and Finite Element (FE) methods in the time and frequency domain, and others. The paper briefly reviews the relative advantages and disadvantages of these simulation tools and contributes to the development of FD methods. One powerful tool - FE analysis - is applied to optimization of plasmon-enhanced AFM tips in apertureless near-field optical microscopy. Another tool is a new FD calculus of "Flexible Local Approximation MEthods" (FLAME). In this calculus, any desirable local approximations (e.g. scalar and vector spherical harmonics, Bessel functions, plane waves, etc.) are seamlessly incorporated into FD schemes. The notorious 'staircase' effect for slanted and curved boundaries on a Cartesian grid is in many cases eliminated - not because the boundary is approximated geometrically on a fine grid but because the solution is approximated algebraically by suitable basis functions. Illustrative examples include problems with plasmon nanoparticles and a photonic crystal with a waveguide bend; FLAME achieves orders of magnitude higher accuracy than the standard FD methods, and even than FEM.

Optical absorption spectroscopy of a single nanoparticle is performed using a spatial-modulation microscope combined with a white-light supercontinuum source. The absolute values of the extinction cross-section of isolated 16nm size gold nanoparticles are determined around their surface plasmon resonance. Measurements performed as a function of the linear light polarization permit to optically identify the properties of an individual particle: size, shape and orientation on the substrate. The statistics of this optically deduced properties are found in excellent agreement with those obtained with transmission electron microscopy.

Highly-ordered two dimensional arrays of monodisperse silver and nickel nanowires were prepared in an alumina matrix. The nearly 100% filling of the template with metal was obtained by improved electrochemical deposition technique. The light propagation in the direction of the long axis of the metal nanowires were studied by far field spectroscopy and the results were compared with the generalized Mie theory. By selectively dissolving the matrix at a constant etching rate the we investigate the surface enhanced Raman scattering (SERS) and the results are interpreted with theoretical models. The enhanced SERS signal can be recorded until the whole matrix was removed and the ordering of the metal nanowires collapses.

Surface enhanced Raman spectroscopy (SERS) has promise as an optical sensor for the detection of chemical and biological agents, in particular when combined with front-end processing for sample preparation prior to analysis. In this paper, we report preliminary results from a SERS analysis of Bacillus cereus T strain (BcT), which was prepared for sensor analysis via a microfluidics-based sample processor. In the microfluidics hardware, low and high molecular weight analytes from a sonicated spore sample were separated via mass-dependent diffusion into two independent microchannels. SERS analysis of the sample outputs revealed a significant separation of the low molecular spore biomarker, dipicolinic acid, from the high molecular weight protein and nucleic acid background. In addition to the processing study, measurements were performed on gold core-shell nanospheres, which are considered a potential SERS substrate for the microfluidic system. Finally, field-induced aggregation of silver nanoparticles, an alternative to chemical aggregation, was shown to be an effective approach for the production of highly enhancing SERS substrates.

Particles several tens of nanometers in size were aligned in the desired positions in a controlled manner by using capillary force interaction and suspension flow. Latex beads 40-nm in diameter were aligned linearly around a 10-μm-hole template fabricated by lithography. Further control of their position and separation was realized using colloidal gold nanoparticles by controlling the particle-substrate and particle-particle interactions using an optical near field generated on the edge of a Si wedge, in which the separation of the colloidal gold nanoparticles was controlled by the direction of polarization.

The optical transmission and distribution through a subwavelength slit on a tapered metallic substrate was investigated. By using a 45° tapered structure, 6 times larger transmission enhancement was achieved compared with a traditional metallic plate structure because of the asymmetric excited surface waves and the matching of propagation constants between the surface waves and slit waveguide. In addition, a focus beam was obtained by patterning surface corrugations in the exit plane. By tuning the period of the surface corrugations, we were able to adjust the focal length with a spot size smaller than the diffraction limit. The focal point can be kept about 0.6μm with a focal length from 0.5μm to 2.5μm for a grating period from 0.5μm to 0.6μm.

The plasmon hybridization method is a powerful approach for calculating the optical properties of composite nanostructures. The plasmons can be viewed as resulting from hybridization of the elementary plasmon modes associated with the different surfaces of the nanostructure. We present applications to metallic core/shell particles, nanoshells with a nonconcentric core and plasmons in metallic films.

In this paper, we discussed the beam focusing of light emerged from a subwavlength metallic slit surrounded by a set of grooves with constant space and width but variant depth at the exit side surface. Based on the numerical model presented by L. Martin-Moreno, F. J. Garcia-Vidal etc. (published in PRL 167401), we attempted to optimize grooves depth to obtain general beam manipulation, such as beam focusing. This attempt did not prove successful for many cases with variant focal length in our optimization practice, although some specific results display agreeable beam focusing with elongated focal depth. Further numerical computation shows that the excited electromagnetic field intensity around groove openings has a strong dependence on the groove depth, but the phase only vary with a maximum change value of π by tuning the groove depth. This property restricts greatly the modulation of electromagnetic field by just changing each groove depth. More geometrical parameters, including groove space and width, are recommended for optimization in the design of nano metallic groove and slit structures for specific beam manipulation.

Excitation of plasmons in a metal nanoparticle leads to localization of electromagnetic fields within the particle, which is expected to result in strong optical nonlinearities. We study ultrafast nonlinearities in optical scattering from single gold nanorods under resonant excitation at the plasmon frequency, and observe changes of as much as 20% in the scattering cross section over the 20-fs laser pulse duration. Unexpectedly, the magnitude of the ultrafast nonlinearity is the same as that due to heating of conduction electrons in the metal.

An aperture-type near-field optical microscope based on hollow-pyramid cantilevered probes has been developed and optimized for ultrafast nonlinear nanospectroscopy applications. These probes have many advantages for near-field microscopy such as higher throughput, higher thermal damage threshold, and absence of pulse chirping. The input pulse duration (as short as 30 fs from a mode-locked, stretched cavity 26 MHz Ti:Sapphire oscillator) is maintained beyond the aperture. Such short pulses, combined with the high peak powers available at the output of hollow-pyramid probes, allow experiments of nonlinear microscopy and spectroscopy with higher spatial and temporal resolution as compared to similar experiments based on optical fiber tips. Results on second-harmonic generation by gold nanostructures and BBO nonlinear crystals are reported demonstrating a spatial resolution down to 100 nm with 40 fs pulses. Implications for local femtosecond time-resolved pump-probe spectroscopy are anticipated.

Electron Energy Loss Spectroscopy in a Transmission Electron Microscope can probe with a high degree of spatial resolution the electronic excitation spectra of nanomaterial over an extended optical spectral range, typically from 2 to 50 eV. Here we describe a derived technique, called Near Field EELS, in which a subnanometer probe of high-energy electrons is positioned at controlled distances from the surface of an individual nano-object. It can then probe the locally induced electromagnetic field at the nanometer scale, which depends on the detailed nature, shape and dielectric response of the investigated nanostructure. This will be demonstrated on different kinds of nanotubes, the atomic structure of which being simultaneously determined by imaging. The obtained spectra can be well modeled within the framework of the so-called continuum dielectric theory. The importance of the coupling between inner and outer surfaces of the nanotubes will be pointed out. Most recent data concern the measurements of the optical gap for Boron Nitride nanotubes of different structural characteristics. Preliminary results on exploration of the electromagnetic fields on individual silver particles with different sizes and shapes, bringing therefore a complementary contribution to plasmonic studies at an unprecedented level of spatial resolution, is presented.

We have fabricated and studied two-dimensional (2D) and three-dimensional (3D) metallo-dielectric photonic crystals (MDPC) in the visible/near ir spectral range using a variety of optical techniques. The 2D MDPC showed anomalous transmission due to surface plasmon polaritons in resonance with the photoluminescence band of a π-conjugated polymer based on a poly-phenylene-vinylene derivative. Consequently we fabricated an organic light emitting diode (OLED) using the 2D MDPC as a cathode with improved performance over an OLED with unperforated cathode. The 3D MDPCs are based on metal infiltrated opal photonic crystals. We studied the reflectivity spectrum of various metal infiltrated MDPCs and found that the reflectivity is low in the visible spectral range but dramatically increases towards the infrared revealing the elusive metallic gap. Our findings are in good agreement with recent theoretical and numerical calculations based on a commercial program.

The numerical study of plasmonic optical objects is of great importance in the context of massive integration of light processing devices on a very small surface. A wide range of nanoobjects are currently under study in the scientific community like stripe waveguides, Bragg's mirrors, resonators, couplers or filters. One important step is the efficient coupling of a macroscopic external field into a nanodevice, that is the injection of light into a subwavelength metallic waveguide. In this article we highlight the problem of the excitation of a surface plasmon polariton wave on a gold-air interface by a diffraction grating. Our calculations are performed using the Green's function formalism. This formalism allows us to calculate the field diffracted by any structure deposited on the surface of a prism, or a multilayered system, for a wide range of illumination fields (plane wave, dipolar field, focused gaussian beam, ...). In the first part we optimize a finite grating made of simple objects deposited on or engaved in the metal with respect to the geometrical parameters. In order to optimize the performances of this device, we propose to use a pattern of resonant particles studied in the second part, and show that a composite dielectric/metallic particle can resonate in presence of a metallic surface and can be tuned to a specific wavelength window by changing the dielectric part thickness.

Recent work in plasmon nanophotonics has shown the successful fabrication of surface plasmon (SP) based optical elements such as waveguides, splitters, and multimode interference devices. These elements enable the development of plasmonic integrated circuits. An important challenge lies in the coupling of conventional far-field optics to such nanoscale optical circuits. To address this coupling issue, we have designed structures that employ local resonances for far-field excitation of SPs. The proposed coupler structure consists of an array of ellipsoidal silver nanoparticles embedded in SiO₂ and placed close to a silver surface. To study the performance of the coupler we have performed simulations using the Finite Integration Technique. Our simulations show that normal incidence illumination at a free-space wavelength of 676 nm leads to the resonant excitation of SP oscillations in the Ag nanoparticles, accompanied by coherent near-field excitation of propagating SPs on the Ag film. The excitation efficiency can by maximized by tuning the aspect ratio of the nanoparticles, showing optimum coupling at an aspect ratio of 3.0 with the long axis (75 nm) along the polarization of the excitation signal. We discuss the origin of these observations.

For nanoscale photonic devices, localized and enhanced optical field as surface plasmon polariton (SPP) is applicable. In conventional devices applying SPP, prism coupler is used for generating SPP on metallic surface. Freely propagating light can be converted to SPP by prism coupler efficiently by matching the phase and the field distribution between light and SPP. However, prism coupler has inferiorities as bulky and uncontrollable SPP manipulations. In this paper, we propose the grating coupler for compact and flexible SPP coupler. The grating coupler is consisted with periodic dielectric structures with 300nm-thickness on flat metallic surface. This can be installed at any position, and the directivity can be controlled by the waveform. On the prating coupler with the pitch of 1500nm and the duty ratio of 0.5, the incident beam with the wavelength of 780nm, p-polarization and the incident angle of 45° was irradiated and that was converted to SPP. In the computer simulations, the insertion coupling efficiency became larger than 60% by adjusting of the insertion angle and the beam waist that were corresponded with the phase matching and field distribution matching conditions. Making the prototypes of the grating couplers, the coupling efficiency was evaluated experimentally. Because of larger focus spot of insertion beam, the coupling efficiency was reduced from the predicted value by computer simulations.

In this work, we study how extraordinary electromagnetic transmission through an array of holes in a metallic film appears as a function of the number of holes and their distribution. In order to do that, we have used a theoretical formalism able to analyze the optical properties of finite collections of apertures placed at arbitrary positions in a metallic film. First, we analyze how the total transmission in a hexagonal 2D hole array evolves as the number of holes in the array is increased. Secondly, we study what is the minimal system showing extraordinary electromagnetic transmission. We find numerically that a linear chain of holes can be considered as the basic entity with extraordinary transmission properties.

A new method for optically exciting and visualizing surface plasmons in thin metal films is described. The technique relies on the use of a high numerical aperture objective lens to locally launch surface plasmons with an area much smaller than their lateral decay length. We visualize directly the intensity distribution of the surface plasmons by detecting the intrinsic lossy modes associated with plasmon propagation in thin films. Our approach allowed us to excite simultaneously a broad spectral continuum of surface waves and to describe for the first time surface plasmon rainbow jets. We quantified the attenuation of the jet as a function of wavelength and film thickness and compared it to the different propagation damping mechanisms. We demonstrated the influence of the interface on the surface plasmon propagation length and demonstrated surface plasmon spectral filtering using molecular excitonic adsorbates.

Photothermal Heterodyne Imaging (PHI) is a highly sensitive optical detection method of individual absorptive nano-objects. It can be applied to absorption spectroscopy measurements Surface Plasmon Resonance spectra of individual gold nanoparticules with diameters down to 5nm were recorded. Intrinsic size effects which result in a broadening of the Resonance are unambiguously observed and analyzed within the frame of Mie theory. Preliminary results obtained with silver nanoparticles are also presented.

We demonstrate a compact optical transducer (~50μm) based on a gold film perforated with a square array of square holes. The lattice constant (separation between nearest holes) is chosen to be a ~1μm to detect refractive index change around (n~1.4) with resonant wavelength (λ~1.5μm). Both reflectance measurement and finite difference time domain (FDTD) simulations are performed to evaluate the performance of the sensors. The responsivity of the resonant wavelength is measured to be Δλ/Δn ~835nm RIU^-1 (RIU= refractive index unit). The linewidth and contrast of resonance are compared with different size of holes from experimental measurement and FDTD simulations. Coupled mode theory analysis is also used to understand the change reflectance spectrum as a function of hole width.

A new surface-enhanced coherent anti-Stokes Raman scattering (CARS) diagnostic of chiral molecules using one-dimensional arrays of metallic nanocylinders is reported. It is found that such structures can be made biresonant, with one resonance arising from guided resonance (GR) of the periodic structure and the another--from the surface plasmon resonance (SPR). Enormous enhancements of the CARS signal can be expected when the pump laser beam is tuned to GR and the emitted anti-Stokes signal is tuned to SPR. Peak field enhancement corresponding to GR is systematically studied for metallic and dielectric nanorods as a function of the incidence angle, material losses, and nanorod diameter. Using coupled dipole approximation (CDA), we provide analytic estimates of the maximum local field enhancements and resonance widths, and find optimum parameters for the field amplification in our essentially two-dimensional geometry. It is shown that the maximum field enhancement at GR is always limited by resistive losses, which can never be completely cancelled by the far-field dipolar interaction. Full electromagnetic simulations supplement CDA-based calculations and qualitatively confirm their findings. Two types of CARS applications are envisioned: one is based on simultaneous enhancement of both two pump waves and of the emission of the anti-Stokes signal, and another one is designed specifically for detection of chiral molecules in crossed fields with very low background noise.

Negative magnetic permeability of split ring resonator (SRR) is theoretically investigated in the optical frequency region. In our calculations, we considered the delay of the current inside the metal SRR in order to estimate the permeability of the SRR precisely; we used the complete formula of the internal impedance, which is valid to the visible range, to estimate the dispersion of both surface resistivity and internal reactance accurately. Our results indicates that in the optical frequency region, the effect of the internal reactance on the magnetic responses of the SRR is more dominant than that of the surface resistivity, because the surface resistivity is already saturated at the frequency lower than 100 THz. At the same time, the internal reactance does not saturate and moves away from zero drastically as frequency increases. From the results, we concluded that the silver SRR array with small capacitance exhibits negative permeability form THz to the visible light region. We also demonstrated that the array of the silver SRRs employing a single ring with divisions exhibits the negative μ at 428 THz (700 nm wavelength).

Metallic nano-slits film is proposed to implement beam manipulation, such as focusing, deflecting and imaging etc. The principle of this novel nano metric device, termed as plasmonic nano lens, is based on the different phase retardation of light when transmitted through a metallic film with arrayed nano-slits, which have constant depth but variant widths. The slits transport electro-magnetic energy in the form of surface plasmon polaritons (SPPs) in nanometric waveguides and provide desired phase retardations of beam manipulating with variant phase propagation constant. Numerical simulations of illustrative examples are performed through finite-difference time-domain (FDTD) method and show its validity as a lens and other potential photonic devices. In addition, extraordinary optical transmission of SPPs through sub-wavelength metallic slits is observed in the simulation and implies higher efficiency than usual binary devices featured with transparent and opaque regions.

We report results of scanning micro-Raman spectroscopy obtained on isolated nanowires and networks of nanowires with different geometries and surface morphologies. We measured a strong, relatively homogeneous, surface enhancement of the Raman response from nanowires with a rough surface morphology, and detected a more sporadic enhanced response detected from smooth nanowires. These results provide the first steps towards the development of selective sensors for hazardous bio- and chemical-agent detection that rely on a combination of electronic conductance measurements and Raman spectroscopic measurements from metallic nanowire networks.

It is known, that along linear chains from silver nano-particles, located in a dielectric matrix, the waveguide modes can propagate in a range of visible light. Such structures recently were investigated with reference to creation of some types of optical subwavelength wave guides. In the present paper the analytical model of a waveguide formed by a one-dimensional array of parallel silver cylinders (this mode has been recently found on the basis of numerical modelling) is suggested. In our work the possibility to use two parallel arrays of cylinders for formation the near-field images of linear light sources in a far zone is considered (an analogue of the ideal lens of J.B. Pendry).

We propose to excite surface plasmon-polaritons using the moving spot of nonlinear polarization created by a laser pulse. Two perspective excitation schemes - with superluminal and subluminal spots - are considered and their efficiencies are compared. These techniques can be used for surface spectroscopy at terahertz frequencies.

A surface plasmon resonance (SPR) sensor for sensing displacement of a thin membrane is described. We assume a thin membrane is located in close proximity of a metal film in the usual SPR configuration. A displacement of the membrane changes the plasmon resonance condition and by processing the reflectance we can deduce the deflection amount. In particular, we analyze the reflectance of this system using Fresnel's formulas for multilayer films and we discuss the angular scanning, differential phase measurement and wavelength scanning methods to obtain the amount of displacement. We propose that such a system can be used as a pressure sensor or an optical microphone. If one uses a cantilever instead of a membrane, same system might have a use in atomic force microscopy applications. The minimum resolvable displacement can be as low as 10^-4Å/√Hz limited by the laser phase noise and the shot noise of the detection system.

In this paper, a novel detection method of sample in liquid is proposed¹. The new idea uses improved Low Pass Filter (LPF) Photonic Band Gap (PBG) cell structure which is layout on Printed Circuit Board (PCB) board^2-3. The disclosed method in this paper demonstrates the method can be applied to measure the concentration of chemical material with advantages of low cost. The observable frequency response experimental results are presented. We also measure all the scattering parameters for the novel waveguide PBG chemical sensor. The disclosed method in this paper demonstrates the possibility for applying photonic band gap structure in designing a frequency division multi-sensor device. A novel coplanar waveguide (CPW) Frequency Division Multiplexer (FDM) applying Photonic Band Gap (PBG) cell combination is designed for L, S, and C-band bandpass outputs on a FR4 substrate. The observable frequency responses of experimental results are presented. The three-band CPW-PBG FDM can be used effectively as a microwave filter component in monolithic microwave integrated circuits (MMIC) for size reduction and rejection of unwanted frequency.

We describe the synthesis of gold nanorods (NRs) nucleated by HgTe nanoparticles (NPs) of average size 3 nm in diameter. Growth of ~200 nm by ~50 nm NRs on various surfaces is achieved by using an intermediary polyelectrolyte layer. A poly(dimethyldiallylammonium) chloride (PDDA) monolayer on the surface attracts the thioglycolic acid (TGA) capped HgTe NPs and assists in one-dimensional gold growth. Rod morphology is observed for approximately one third of the resulting features. Confirmation of Au deposition is obtained with x-ray photoelectron spectroscopy and optical absorption measurements that show an increase in the Au plasmon band with time spent in gold growth solution. Au NRs were grown directly on the surface of high quality factor (Q) optical resonators (microspheres and microcylinders). Although the coating procedure reduces the Q of the resonators, whispering gallery modes are sustained. This seeding technique, amenable to many different surfaces, may result in semiconductor-metal nanocomposites with novel electronic and optical properties.

We have observed experimentally the anomalously large light transmission through a continuous gold film with various PMMA surface dielectric gratings deposited on top of the film. The spectra of these samples have been measured for different incident and scattered angles. Enhanced transmission through the film is attributed to the excitation of various surface plasmon modes. Both symmetrical and anti-symmetrical surface plasmon dispersion relations have been applied to analyze the transmission spectrum. Similar anomalous transmission effects have been observed in light transmission through gold-chalcogenide glass (As₂S₃) interfaces after grating formation in the chalcogenide glass using two-beam interference with strong pump light. Enhanced transmission is demonstrated using a weak probe beam. These observations demonstrate the possibility of all-optical signal processing using enhanced anomalous light transmission through metal films.

Highly sensitive measurement of biomolecules is very important in clinical diagnosis and biomedical sensing. Spectroscopic methods have played important roles in biomedical sensing system developments. Recent development in surface enhanced Raman scattering (SERS) method has greatly enhanced the weak Raman signals of biomolecules and has provided great potentials for real time measurement of biomolecules of body fluid. In addition, Raman measurement has the advantage of not requiring extrinsic fluorescent marker for labeling purpose. In this study, we have pioneered in the development of SERS spectroscopic measurement technique for serum lactic acid, which is one of the most important metabolic parameter in blood. We have fabricated Ag colloidal nanoparticles to enhance the weak Raman signal of lactic acid in serum. The diameter of the Ag nanoparticle is 20 nm, the nanoparticles concentration is 10⁹particles/ml. We have observed the SERS characteristic peak of lactic acid at 1285~1480cm^-1 under 632.8 nm HeNe laser excitation. We have demonstrated the measurement of the lactic acid in filtered serum in the physiological concentration range 5x10^-3~22x10^-3 mole/L, which is hundred times lower than the detectible range using traditional Raman approach. The serum samples with were measured in a specially designed reflector type sample holder to form a multiple reflection of excitation laser through the sample, between a reflector and a notch filter. In conclusion, this research demonstrates the feasibility of using Ag SERS technique for measuring the lactic acid at physical concentration and establishes the platform technique for human body fluid measurements.