This PDF file contains the front matter associated with SPIE Proceedings Volume 7033, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

"Nanophotonics" uses the local interaction between nanometric particles via optical near-fields to bring "qualitative innovation" to the field of optical technology. Optical near-field interactions respond hierarchically at the nanometer scale, allowing unique nanophotonic functions. We defined two kinds of hierarchical optical near-field interactions: those between optical far- and near-fields, and those in the optical near-field only. We demonstrated these hierarchical effects numerically and experimentally using several prototype "nanophotonic architectures." The first, a "hierarchical hologram," operated in both the far- and near-fields with few adverse effects. We also demonstrated hierarchical effects in the optical near-field by core-shell metal nanostructures. Hierarchical nanoscale architectures could allow single optical devices to perform multiple functions. The practical realization of such devices could have a major impact, for example, in the field of optical security.

Surface relief gratings produced on planar substrates have been widely investigated for their application as a holographic recording medium. Much of this work has concentrated on gratings made in polymer thin films with an azo-benzene group. We describe a novel phenomenon involving surface relief gratings which are formed by deposition of Rhodamine 6G dye on polybutadiene thin film. This deposition as a grating pattern is photo-induced in a dye-solution by holographic interference of low power 488 nm light from an argon-ion laser. Dynamics of this aqueousphase grating deposition is investigated for various concentrations of the dye. A plausible mechanism of grating formation involves photochemical reaction of polybutadiene substrate with the laser-excited dye. Surface relief structure of the grating is characterized with an atomic force microscope.

We present a tip-enhanced Raman spectroscopy (TERS) system that permits efficient illumination and detection of optical properties in the visible range to obtain high contrasts Raman signals from strained silicon (ε-Si) assembled on silicon germanium substrate using an edge filter. The cut-off investigation in a depolarized TERS configuration. We overshadow wavelength of the edge filter is tuned by changing the angle of incident beam to deliver high incident power and effectively collect scattered near-field signals for nanoscopic strong far-field background signals from Raman active materials by utilizing the results obtained from depolarized surface-enhanced Raman scattering experiments in conjunction with silicon Raman tensor calculation to quantify which polarizer, analyzer and sample azimuth combination gives the minimum far-field signals. Here, we utilize the s-polarization instead of p-polarized light in conjunction with polarization properties of ε-Si to obtain a high contrast Raman signal. We found that for imaging Raman active and bulk crystalline materials such as silicon, background signal suppression (s-illumination) is more important than the field enhancement with strong far-field signal levels (p-polarization). The utilization of an edge filter for shorter collection time, depolarized configuration for higher contrast and tip heating for higher resolution are discussed.

We show a different approach to perform near-field Raman imaging with sub-diffraction limit spatial resolution. In this approach, a dielectric microsphere is trapped by the excitation laser through optical tweezers technique. The microsphere is used to focus the laser to the sample, and also to collect the scattered Raman signals. We show the capability of this method in imaging various types of samples, such as device sample with 45 nm poly-Si gates with SiGe stressors and gold nanopatterns. This method is easy to perform, has better repeatability, and generates stronger signal as compared to the conventional near-field Raman techniques.

We present theoretical studies and experimental results on the optical properties of gold, octahedra-shaped nanoparticles. We show that the optical spectrum varies quite dramatically as two nanoparticles are brought into close proximity. AFM images and optical spectra have been obtained for nanooctahedra dimers in uncoupled and strongly coupled configurations. The former displays a single peak in the optical spectrum, while the latter shows an additional peak at longer wavelengths. Calculations indicate that the additional spectral feature originates from a strongly coupled plasmon state that oscillates along the extended axis of the dimer. We investigate theoretically the distances over which the dimers couple and find these results to be particularly orientation dependent. The anisotropic particle shape and sharp apices contribute significantly to the orientational dependence of the interparticle couplings.

Recently plasmonic biosensors consisting of gold nanoparticles have been developed. In order to understand the response of the biosensors, we have investigated how are gold nanospheres immobilized on a surface covered by a self-assembled monolayer (SAM) which is formed by immersion of the substrate in a solution, by use of surface second-harmonic generation (SHG). The surface immobilized gold nanospheres (SIGNs) are supported by a self-assembled monolayer (SAM) of aminoundecanthiol on a gold thin film. The SIGN substrate was immersed in an ethanol solution of hemicyanine-terminated alkanethiol. The capping angles of the hemicyanine SAM with respect to the top of the SIGN were evaluated from polarization dependence of SHG intensity. The SIGNs are not fully covered with the SAM, and the capping angle is found to be approximately 120 degrees.

Surface plasmons enable the transmission of optical information in confined geometries, inaccessible for diffraction-limited far-field light, while having high signal bandwidth and propagation speed like conventional optics. These advantages have resulted in novel applications for surface plasmons, such as offset-apertured near-field scanning optical microscope (NSOM) probes. A subwavelength aperture couples surface plasmons that illuminate the tip apex of an adjacent metal-coated tip, which results in a single-lobed probing optical spot having a full-width half maximum (FWHM) similar to the apex diameter. Since the surface plasmons converge at the apex, an offset-apertured probe promises stronger localized electric fields than an apertured NSOM having comparable FWHM. Additionally, the subwavelength aperture does not permit the passage of far-field light, reducing the background signal in comparison to apertureless NSOM probes. For other applications, the ability to selectively switch a waveguide "on" or "off" is desired. Optical-optical switching for selective surface plasmon coupling would ideally permit high-speed switching on a small scale. Two nodes are presented as means to perform switching of four planar thin surface plasmon waveguides by interfering TEM₁₀, TEM₀₁, and TEM₀₀ light beams normally-incident upon a node. One node uses a flat-apexed pyramidal reflector to reflect the incident light toward the waveguides' ends. An alternative node is a simple square aperture, which couples surface plasmons through light diffraction at the aperture's edges. Individually turned-off waveguides are shown to have their coupled power attenuated by at least -10 dB.

Waveguiding by dielectric-loaded surface plasmon-polaritons (DLSPP) structures are numerically and experimentally investigated. We used the effective index model to understand the influence of basic waveguide parameters such as width and thickness on the properties of the surface plasmon guided modes. A waveguide was fabricated and experimentally studied. The effective indices of the modes supported by the waveguide and their propagation length are evaluated by leakage radiation microscopy in both the Fourier and imaging planes. Several excitation schemes were tested including surface plasmon coupling by diascopic or episcopic illumination as well as defectmediated excitation of guided modes. We found good agreement between theoretical values predicted by the effective index model and experimental values deduced from leakage radiation images.

Channel plasmon polaritons (CPPs) propagating along the bottom of subwavelength grooves cut into a metal surface were recently shown to exhibit strong confinement combined with low propagation loss, a feature that makes this guiding configuration very promising for the realisation of ultra-compact photonic components. Here, the results of our investigations of CPP guiding by V-grooves cut into gold are presented, demonstrating efficient large-angle bending and splitting of radiation as well as waveguide-ring resonators and Bragg grating filters.

We have analyzed the characteristics of three types of gap plasmon waveguides having wavelength selective functions: one is structured by a Fabry-Perot resonator with reflectors, one is structured by a slot resonator and the other is the waveguide with a single or two stubs. We have presented the numerical results of the transmittance spectra for these structures calculated by using the finite-difference time-domain method. The numerical results have clearly indicated that all structures of a sub-micron size work properly as wavelength selective devices. The advantage of a stub type of waveguide is on easiness in fabricating, while that for a Fabry-Perot type of waveguide is to lead to making the size decrease considerably and relatively high Q-factor.

Electromagnetic wave propagation in structured metals has attracted strong attention in wide wavelength regions from microwave to visible. We have investigated transmission properties of metal hole arrays and related structures in the terahertz region by using the terahertz time-domain spectroscopy (THz-TDS). We have found a variety of transmission properties depending on the periodic structure of metals, i. e. extraordinary transmission, large polarization conversion, large optical activity, etc. Some of the properties are explained by the surface plasmon-polariton and/or the local structure of holes.

Metal gap optical waveguides support propagation and strong confinement of coupled surface plasmon polariton in nano-region. We study efficient transmission through a plasmonic T-branch with a mesa structure in metal gap optical waveguides. Transmissivity through the branch with various mesa geometries is investigated by numerical simulations. It is found that transmissivity through the branch can be improved by introducing thin metal barrier into dielectric gap. We can achieve more than four times enhancement in the transmissivity.

Herein we perform three-dimensional finite-difference time-domain calculations on an isolated micron size slit in a thin gold film to study the behavior of confined electromagnetic fields for TM, TE, and circular incident polarizations. It is found that the electric and magnetic fields exhibit well defined standing wave patterns inside the slit. Moreover, the electric and magnetic fields are seen to be out of phase, and the power flow through the slit is governed mainly by the magnetic field for TM polarization and the electric field for TE and circular polarizations. To understand these results a theoretical modal expansion of the fields in the presence of the slit is done. It is found that the standing wave patterns and dephasing can be attributed to a superposition of propagating and evanescent waveguide modes.

The optical extinction spectra of single gold nanorods are investigated using a spatial modulation spectroscopy technique. The experimental results are compared to the computed spectra of nanoellipsoids using the dipolar approximation or a generalization of the Mie theory, focussing on the width of the longitudinal surface plasmon resonance. This is shown to be consistent with that deduced from the theoretical models using different available sets of dielectric constant for bulk gold, without introducing surface broadening effect. Extension of this approach to investigation of the ultrafast nonlinear optical response of a single gold nanorod is also discussed.

Image dipole effects are highly dependent on the polarization direction, constructive (destructive) for the vertical (horizontal) dipole with respect to the interface, respectively. Polarization resolved detection of light scattered off a gold nano particle functionalized tip on a flat gold surface enables the study of the image dipole orientation effects on the scattering type near field scanning optical microscope signal. A propagating surface plasmon polariton as an excitation source sufficiently reduced the large background by virtue of its evanescent nature capacitating the quantitative description of the image dipole. At large tip-to-sample distances, the Fabry-Perot like interference between the radiations from the GNP and from the image dipole induced at the flat gold surface, are evident. The horizontal- polarization and vertical-polarization Fabry-Perot oscillations, however, are out-of-phase with each other. As the tip approaches the surface, the vertical component get further enhanced while the horizontal one gets suppresses, demonstrating the polarization reversal of image dipole as predicted by theory.

We have conducted a theoretical and calculational study of the transmission of light through a sub-wavelength-perforated metal film, as well as through a homogeneous metal film, with Drude ac conductivity tensor in the presence of a static magnetic field. Both perforated and homogeneous metal films are found to exhibit a magneto-induced light transparency and a decreasing of reflectivity due to cyclotron resonance. In particular, the cyclotron resonance and the surface plasmon resonance of a perforated metal film move to higher frequencies with increasing magnetic field, bringing about large changes in the extraordinary light transmission peaks predicted to occur in such a film. In the case of periodic microstructures, these phenomena depend not only on the magnitude of the applied in-plane magnetic field, but also on its direction. This is due to the nonlinear dependence of the local electromagnetic response on that field. The practical possibility of changing the sample transparency by application of a static magnetic field (e.g., a new type of magneto-optical switch) is discussed.

This report presents an overview of our study on the optical transmission and thermal light emission properties of sub-wavelength hole arrays fabricated in a square lattice with 4 μm periodicity. The structures were fabricated in thin aluminum (Al) films on silicon (Si) substrates using conventional photolithography. The spectra were obtained using a Fourier transform infrared spectrometer with a port for an external cryostat configured for thermal emission measurements. The perforated films showed extraordinary transmission bands in the mid-infrared spectral range, which could be well explained as due to light coupling to surface plasmon-polaritons on the two film interfaces. We fitted the transmission spectra and calculated the absorption spectra of these structures using a model for the dielectric response that utilizes an effective plasma frequency determined by the individual holes, as well as several resonant modes associated with the reciprocal vectors in the lattice structure factor. We found that the thermal emission spectrum from the perforated films followed the transmission spectrum characteristics, rather than the obtained absorption spectrum; in apparent contrast to Kirchhoff's law of radiation. We conclude that the perforated films behave as radiation filters, where the thermal emission radiation is suppressed in the frequency range outside the transmission resonant bands in the spectrum.

This paper reviews recent advances in plasmonic active metamaterials working in the terahertz frequency band and their applications to functional devices including sources, detectors, intensity modulators, and frequency multipliers. The proposed device incorporates doubly interdigitated grating gates with super sub-wavelength feature size into a high electron mobility transistor to form periodically confined two-dimensional plasmon (2DP) cavities in a metamaterial, succeeding in the first observation of stimulated emission of terahertz radiation at room temperature. Optoelectronic control of the 2DP dispersion will open a new aspect of ultra-broadband signal processing in the terahertz regime.

Plasmonic metamaterials provide a convenient experimental platform for demonstration of principles of transformational optics. Design and performance of two-dimensional focusing and imaging devices based on plasmonic metamaterials are described. Depending on frequency, these devices may operate both in the normal lens and the superlens mode. Negative index imaging and guiding of surface waves using layered plasmonic metamaterials is demonstrated. ε near zero metamaterial is realized.

We have developed thermal emitters of linearly polarized and narrow-band mid-infrared light based on highly controlled plasmon resonance in narrow and deep rectangular Au gratings. This optical source is a series of one-dimensional metal-insulator-metal optical cavities with a closed end. This characteristic results in the control of the thermal radiation, emitting a narrow infrared spectrum at a specific wavelength of 2.5-5.5 micro-meters. The wavelength is specified 100nm wide, 1000nm deep dimensions of the cavity were accurately manufactured. The maximum emittance reaches 0.90, and the FWHM/wavelength of the peak is as narrow as 0.13-0.23. Furthermore, we have demonstrated simple chemical analysis based on orthogonally polarized two-color infrared waves emitted from an integrated grating. This simple emitter is expected to play a key role in the infrared sensing technologies for analyzing our environment.

We discuss a family of nanoscale cavities for electrically-pumped surface-emitting semiconductor lasers that use surface plasmons to provide optical mode confinement in cavities which have dimensions in the 100-300 nm range. The proposed laser cavities are in many ways nanoscale optical versions of micropatch antennas that are commonly used at microwave/RF frequencies. Surface plasmons are not only used for mode confinement but also for output beam shaping to realize single-lobe far-field radiation patterns with narrow beam waists from subwavelength size cavities. We identify the cavity modes with the largest quality factors and modal gain, and show that in the near-IR wavelength range (1.0-1.6 μm) cavity losses (including surface plasmon losses) can be compensated by the strong mode confinement in the gain region provided by the surface plasmons themselves and the required material threshold gain values can be smaller than 700 cm^-1.

We review recent advances achieved in the field of integrated optical manipulations based on the control of surface plasmons. In particular, we describe how intense and confined optical force fields can be precisely engineered in the vicinity of transparent surfaces patterned with plasmonic metal structures.Recent progresses in the design of such devices is presented together with the latest experiments that have demonstrated efficient trapping of micro-objects under reduced laser intensity compared with conventional optical tweezers. Finally, we review other proposals where the use of localized surface plasmons in coupled metal nanostructures opens new perspectives in scaling down the trapping volumes well below the diffraction limit for the manipulation of single nano-objects.

We investigate the reflectivity of glass thin films with different nanostructures using electromagnetic theory. The Discrete Dipole Approximation (DDA) method is used in the calculations. The thickness of the film is varied from 50 to 200 nm. Films composed of semi-ellipsoid, cylinder, and prism particle arrays are examined in order to understand the structure dependence of the thin film reflectivity at nanoscale level. When the film thickness is 50 nm, films with effective dielectric constant gradient exhibit lower reflectivity than those with the uniform dielectric constant. At short wavelengths, the thin film nanostructure has a significant influence to its reflectivity. For longer ones, especially when the wavelength is much larger than the film thickness, the effect of the nanostructure becomes less important and the volume of the film evolves to be an important factor. We also explore the reflectivity of glass films including a 100 nm thick solid substrate layer and nanostructures of different heights. For a film with semi-ellipsoid arrays of the same thickness, its reflectivity drops with the increase of the semi-ellipsoid diameter. The simulation results can be of help in the design of thin film solar cell coating for the enhancement of solar energy conversion efficiency.

A variety of approaches are examined for exploiting the optical properties of metal or dielectric nanoparticles, particularly those associated with surface plasmon polariton resonances, to improve the performance of semiconductor photodetectors and photovoltaic devices. Early and recent concepts for employing optical absorption and local electromagnetic field amplitude increases associated with surface plasmon polariton excitation to improve photocurrent generation in organic photovoltaic devices are briefly reviewed. The application of optical scattering properties of nanoparticles to improve transmission of optical power into, and consequently photocurrent response in, Si and a-Si:H photodiodes is then described, and effects related to scattered-wave phase shifts and interference effects between scattered and directly transmitted wave components in producing either enhancement or suppression of photocurrent response at different wavelengths are discussed. Coupling of photons incident normal to the surface of a semiconductor thin-film device into lateral, optically confined paths within waveguide structures formed by refractive index contrast either within the semiconductor structure, or between the semiconductor and surrounding dielectric material, is discussed in the context of early and recent studies of such coupling in silicon-on-insulator photodetectors, and recent work on engineering of photon propagation paths in III-V compound semiconductor quantum well solar cells.

We report on the fabrication, experimental characterization and modeling of atomic force microscope (AFM) probes with pyramidal optical antennas fabricated at the ends of the tips. These are being developed for tip-enhanced near-field scanning optical microscopy. We use focused ion beam milling to etch a gold-coated Si₃N₄ AFM tip, resulting in a pyramidal gold nanoparticle (188 - 240 nm long) at the end of the tip. Using finite-difference time-domain (FDTD) simulations, we estimate the electric field distribution around the nanoparticle as a function of incident wavelength for nanoparticles of various lengths. We experimentally measure the scattering spectra of fabricated probes and show enhanced scattering associated with the localized surface plasmon resonance of the tip. Both simulations and experiments show that an increase of the tip length results in a redshift of the tip resonance wavelength. These pyramidal metal nanoparticle tips could be used for either mapping the field distribution of nanophotonic devices or high spatial resolution spectroscopy.

A simplified analytic model is employed to demonstrate how surface plasmons propagating between the slits in Young's interference experiment can modulate the spatial coherence of the light field radiated by the two slits. The model is verified by comparison with results from rigorous numerical simulations. Our simulations reveal that the coherence can indeed be enhanced or suppressed, depending on the distance between the slits. Extending our analysis to a three-slit geometry, the effect on the degree of modulation when another slit is placed between the two slits is investigated. It is found that, compared to the two-slit case, the center slit serves not only as a barrier that can reduce the modulation, but can also act to enhance the amount of modulation. These results are promising for the development of novel "coherence converting" devices with suitable metallic arrays of subwavelength apertures.

The shapes of initially spherical Ag nanoparticles in glass were permanently changed by fs laser irradiation. This shape transformation of the nanoparticles results in an optical dichroism of the material, strongly depending on the actual irradiation parameters such as intensity, number of pulses per irradiated spot and laser wavelength. The proposed technique allows modifying the optical properties of glass containing metallic nanoparticles and can be used for the production of dichroic or polarizing microstructures in the visible and near infrared region with high polarization contrast.

We present a variable-focusing surface plasmon dielectric lens using the air-gap modulation. Based on the modal analysis of the planar slab waveguide consisting of the dielectric slab over the metal substrate, we examine the transmission characteristics of the single air-metal surface plasmon polariton (SPP) mode through the planar slab waveguide. Our simulation results reveal that the 2π modulation of the phase of the transmitted SPP mode can be realized. By using the lens with parabolic shape, the SPP mode converges and focuses to one point. It is shown that the dynamic modulation of the air-gap width gives rise to the dynamic change in the focal length.

We have fabricated gold nanospheres composite multilayer films using the layer-by-layer (LbL) self-assembly technique, and have investigated the aggregate states of the gold nanosphere. The gold nanospheres composite multilayer films were fabricated by controlling the gold nanosphere layers with polyelectrolyte layers, and were characterized with linear and nonlinear optical spectroscopy. The transmission absorption spectra and scanning electron microscopy (SEM) images show modifications of the optical properties arising from the aggregate states of the gold nanospheres. The strong longitudinal resonance mode was observed when the gold nanospheres form aggreagates. Intense optical second-harmonic generation (SHG) was observed from the gold nanosphere aggregates of which surface was covered with a hemicyanine self-assembled monolayer. This high SHG response originates from the strong interaction via localized surface plasmon enhancement of the gold nanosphere aggregates. The gold nanosphere aggregates are promising for applications to optoelectronic devices and surface-enhanced spectroscopy.

We propose a localized surface plasmon microscope that uses a zeroth-order Bessel beam for the illumination to employ a beam scanning method. The microscope visualizes the refractive index distribution in the optical near-field from a substrate surface by measuring the coupling strength between illumination light and surface plasmons from the light absorption. The beam scanning method utilizing a galvano mirror for the fast scanning axis increases the repetition rate up to 2 kHz. In order to confirm imaging properties of the developed microscope, we observe the point spread function by using a latex particle with the diameter of 175nm. It is revealed that the properties of the observed point spread function coincide with that of the calculated intensity distribution of the electric field.