We have measured the propagation distances of wedge plasmons and two-dimensionally localized gap plasmons (GPW) at a vacuum wavelength of 632.8nm. The measured propagation distances of the wedge plasmons increased from 2.2μm to 3.1μm with increasing the wedge tip radius from 20nm to 125nm. The GPW has the measured propagation distance of 8.2μm for a gap width of 100nm and 900nm height. We have developed a finite-difference time-domain (FDTD) method represented by the spherical coordinates which is applicable for numerical calculations of nonlinear optical responses. This FDTD technique gives information about time-dependent spatial distributions of light intensity in nonlinear metallic particles and we can deeply understand nonlinear optical phenomena related with localized surface plasmons in a spherical particle.

Wedged negative dielectric gap waveguide has been studied theoretically. FDTD simulations show adiabatic wavenumber conversion in coupled mode of surface plasmon polariton along the wedged structure. In addition, field enhancement has been observed at the output of the wedged structure even in large propagation loss of metals. We propose wedged negative dielectric gap waveguide as an efficient nano-optical coupler between optical fibers to nano-optical circuits. Propagation modes in metal gap waveguide formed on a prism have been studied experimentally by using attenuated total reflection method.

Long-range surface plasmon polariton (LRSPP) waveguides supporting both TE and TM polarized light are demonstrated experimentally. The waveguides consist of metallic nanowires with approximately 150-nm square cross sections embedded in a polymer matrix. The wavelength dependence of propagation loss and coupling loss to single mode fibers is presented. At wavelengths around 1550 nm, the nanowires exhibit a propagation loss around 4.0 dB/cm for the TM mode and 4.5 dB/cm for the TE mode. The mode field is close to symmetric and suitable for coupling to and from optical fibers. A small increase in the waveguide width, resulting in a deviation from a square cross section, is sufficient to extinguish the TE mode, making asymmetric nanowire waveguides similar to the more conventional LRSPP thin stripe waveguides. Finally, we demonstrate a compact thermo-optical variable optical attenuator based on a LRSPP nanowire waveguide.

We have numerically investigated characteristics of plasmonic waveguides for coupled wedge plasmons (CWPs) consisting two silver wedges separated by a nano gap all on a glass substrate. Three types of waveguides for CWPs on a glass substrate are considered: (1) two metallic wedges on a planar substrate, (2) two metallic wedges built into the substrate and (3) two-folded free-standing metallic wedges. For numerical calculation, we have employed the Drude model for the dielectric constant of silver and the excitation light with the vacuum wavelength of 632.8 nm. The refractive index of the glass n_s is fixed at n_s = 1.5. We have calculated field distributions in the waveguide as well as dependence on changing the gap w between wedges and the wedge angle θ. CWPs eigenmodes of such structures are shown to exist and propagate along waveguides structures employed here. The propagation constant k_//, propagation distance L and the beam area of a CWP depends on w and θ. L and the beam area size for waveguide employed here are in the order of 10 μm and in the range from 10^-4 μm² to 10^-1 μm², respectively. These values mean that waveguides for CWPs have a potential to be utilized for the nano optical waveguides in future.

In our attempt to reveal highly localized field enhancements on random metallic films using near-field scattering probe microscopy we experimentally demonstrated the existence of narrow peaks when using a monochromatic illumination. In order to get a better understanding of the second harmonic generation taking place on such films we have undertaken the same kind of near-field experiments using femtosecond lasers sources with high peak power able to induce the non linear response. These lasers have a spectral bandwidth associated with the pulse duration, which is in the femtosecond range. With such spectral broadening we have observed, as expected, a spatial broadening of the peaks at ω, which spread over distances in the 100-500 nm range. The behavior of the peaks is quite different at 2 ω: they are found to be always very well localized (~10 nm) despite of the polychromatic nature of the light; moreover there is no clear correlation between the peaks position at ω and those at 2 ω. This observation indicates, as often underlined in non linear processes, that coherent interactions involving a distribution of available frequencies in the lasers spectra take place. These frequencies ωn, coherently induce second harmonic generation as long as ω_n + ω_m = 2 ω.

Nearfield scanning optical microscopy (NSOM) offers a practical means of optical imaging at a resolution well beyond the diffraction limit of the light. However, its applications are limited due to the strong attenuation of the light transmitted through the sub-wavelength aperture. To solve this problem we report the development of plasmonic nearfield scanning optical microscope with a high optical coupling efficiency. By exciting surface plasmons, plasmonic NSOM probes are capable of focusing light into a 100 nm spot. Both numerical simulation and nearfield exposure experiments have demonstrated that the intensity at the focal point is at least 10 times stronger than can obtained from the conventional NSOM probes under the same illumination condition. By providing a strong nano-scale light source, plasmonic NSOM can be used as a high speed nano-scale imaging tool for cellular visualization, molecule detection, and many other applications requiring high temporal resolution.

Molecular interactions occurring on or near cell membrane surfaces are expected to have different properties from those occurring in bulk solutions. In order to analyze molecular interactions between the cell membrane with biomolecules having no additional fluorescence labeling, a microscope based on the integration of surface plasmon resonance (SPR) and common-path phase-shift interferometry (PSI) techniques is developed and used to study the cell adhesion and migration on the biosurfaces. The surface plasmons are excited by light via the attenuated total reflection method. The common-path PSI technique has features of long-term stability, even when subjected to external disturbances. Hence, the developed SPR phase microscope meets the requirements of real-time kinetic imaging. The proposed common-path SPR-PSI microscope demonstrates a detection limit of 2x10^-7 refractive index unit and a long-term phase stability of 2.5x10^-4 π root mean square over four hours. The developed microscope is successfully applied to the real-time observation the live cell membranes with thrombomodulin proteins.

The resonance enhanced Goos-Hanchen shifts at attenuated total internal reflection enables the possibility for highly sensitive surface plasmon resonance sensor. The observed giant displacements result from the singular phase retardation at the resonance where the phase is continuous but changes dramatically. The phenomenon is proposed for chemical sensing and the superior sensitivity is demonstrated.

C-reactive protein (CRP) produced by the liver is one of the most characteristic acute-phase proteins. It has been suggested that the level of CRP in human serum may be a significant tool of detecting risks of developing cardiovascular disease and atherosclerosis. Here we propose an advanced plasmonic surface plasmon resonance (SPR) bioassay with Au nanoparticles embedded in the dielectric film that demonstrates a 10X improvement in resolution compared to the conventional SPR biosensor. The co-sputtered film was modified with (3-Aminopropyl)triethoxysilane to sequentially immobilize protein G, monoclonal anti-CRP antibody (C8), and human serum albumins (HSA). After blocked by ethanolamine, the sensor was used to detect CRP. Using this extremely sensitive biochip, the lowest reliable concentration of CRP without any exterior labeling is simplified to human physiological level. The novel assay has the latent capability of not only eliminating the disturbances coming from serum proteins resulting in false signals, but is also able to be applied in rapid and label-free clinical detections of CRP with large improved sensitivity.

Modification of metal nanoparticles with laser light has been a well-known technique for several years. In this paper, we present our recent studies on tailoring the shape of colloidal gold particles with nanosecond-pulsed laser light. The underlying method is based on the shape and size dependent optical properties of metal nanoparticles, i.e. the excitation of surface plasmon polariton resonances. Thus, laser irradiation with a pre-determined photon energy excites and heats nanoparticles of certain shapes and sizes selectively. This heating leads to diffusion and, for sufficiently high fluences, to evaporation of surface atoms. In our experiments, colloidal gold particles were prepared by chemical reduction of a gold salt resulting in nanoparticles with different sizes and shapes. Subsequently, the colloidal gold particles were irradiated with nanosecond-pulsed laser light. In all cases, a significant reduction of the line width of the surface plasmon polariton resonance has been observed. This reflects a narrowing of the shape distribution of the particles. For example, irradiation with a photon energy of 2.16 eV and a fluence of (58 ± 2) mJ/cm² leads to a reduction of the width of the surface plasmon resonance from 0.30 eV to 0.22 eV (HWHM) due to a reshaping of the nanoparticles. This has also been confirmed by TEM measurements. Also, a size reduction of the nanoparticles has been observed.

Molding the flow of light at the sub-wavelength scale has always been one of the greatest challenges of photonics, as it would allow the realization of optical circuits with a degree of integration similar to that achieved in integrated electronics. Strongly localized eigenstates of an electromagnetic (EM) field exist in small clusters of regular metallic inclusions embedded in an otherwise uniform dielectric host. The electromagnetic field can be restricted to have large amplitude in spatial regions whose linear size is much smaller than the wavelength. This ultra-localization of an EM field is achieved with the help of surface plasmons in the metallic inclusions. These plasmons screen the EM field, essentially cancelling it outside the volume of the eigenstate. This phenomenon has been proposed as the basis for a SPASER device, namely, Surface Plasmon Amplification by Stimulated Emission of Radiation. This SPASER would be a source of strong, coherent EM radiation with a size that can be much smaller than the wavelength. In this report we present results for such states which go beyond the quasi-static approximation. That is necessary in order to analyze the radiative and dissipative properties of those states, e.g., the radiative and dissipative losses.

Near-field Raman scattering has been successfully utilized to study the interaction between a metal-coated nano-tip and carbon nanostructures, such as carbon-60 molecules and single walled carbon nanotubes. The enhanced and localized light field in the vicinity of the tip apex provides high resolution imaging as well as the detection of weak vibrational modes. Apart from the electromagnetic and chemical interactions, a mechanical interaction between tip molecules and the sample molecules has also been investigated.

Nanoscale characterization of strained silicon is essential for developing reliable next generation integrated circuits. Vibration mode of Si-Si in strained silicon was selectively enhanced to be observed by surface enhanced Raman spectroscopy technique. Covering the silver island film on a strained silicon layer Raman signal from the strained silicon can be detected with a high sensitivity against the overwhelming background signal from the underlying silicon layer. This technique allowed us for micro-Raman spectroscopy on strained silicon, and is straightforward to nano-Raman spectroscopy by tip-enhanced Raman microscope in which a sharpened metallic tip is used instead. We observe localized strains in strained silicon by tip-enhanced near-field Raman spectroscope in reflection-mode. The tip-enhanced Raman spectra show that the Raman frequency and intensity of strained silicon were different within a crosshatch pattern induced by lattice-mismatch. Micro Raman measurements, however, show only uniform features because of averaging effect due to the diffraction limit of light.

The aligned silver nanorod array substrates prepared by the oblique angle deposition method are capable of providing extremely high enhancement factors (~108) at near-infrared wavelengths (785 nm) for a standard reporter molecule 1,2 trans-(bis)pyridyl-ethene (BPE). The enhancement factor depends strongly on the length of the Ag nanorods, the substrate coating, the polarization of the excitation light, as well as the incident angle. With the current optimum structure, we demonstrate that the detection limit for BPE can be lower than 0.1 fM. The applicability of this substrate to the detection of bioagents has been investigated by looking several viruses at low quantities (~0.5uL). Different viruses have different fingerprint Raman spectrum.

Tip-enhanced Raman spectroscopy (TERS) using side illumination is a promising spectroscopic tool for nanoscale characterization of chemical composition, structure, stresses and conformational states of non-transparent samples. Recent progress has shown signal enhancements for a variety of samples, including break-through enhancements of semiconductors. In this work, optimization of the polarization geometry increases contrast between near-field and far-field signals on Si and improves imaging quality. Two-dimensional images of semiconductor nanostructures show reasonable agreement between topographical and TERS images. These recent TERS results using both silver- and gold-coated tips demonstrate localization of the Raman enhancement to within approximately 20 nm of the tip. Also, the enhanced Raman signal of a strained Si layer is separated from an underlying Si substrate, which is encouraging for potential strain distribution analysis of silicon nanostructures.

Using the Plasmon Hybridization (PH) method and the Finite-Difference Time-Domain (FDTD) method, we investigate the plasmonic properties of finite metallic nanopartices interacting with extended metallic substrates such as thin films and wires. The results from the two computational methods are found to agree very well. We show that the plasmons of a metallic nanoparticle couple to the delocalized plasmons of extended substrates in the same manner as an electronic impurity level couples to an continuum of electronic states. The interaction can result in both localized plasmons and virtual states in the plasmonic continuum. The virtual states are composed of delocalized plasmons from the extended substrate and depend sensitively on the geometry of the system, the polarization of incident electromagnetic excitations as well as the background dielectric properties of the structures. We demonstrate that the virtual state can provide large electric field enhancements over a broad and tunable spectral regime. Our investigations show that plasmonic structures supporting virtual states are highly suitable as substrates for surface enhanced spectroscopic applications and may be useful in plasmonic waveguiding applications.

Different arrays of Ag-nanoparticles grown on anodic alumina nanochannels with precisely tunable gaps (5~25 nm) are exploited for surface-enhanced Raman spectroscopy (SERS). The enhancement becomes significant for gaps below 10 nm and turns dramatically large when gaps reach an unprecedented value of 5 nm. The results are quantitatively consistent with theories based on collectively coupled surface plasmon. Such nanofabricated substrates with consistently uniform and large dynamic range have many chemical/biological sensing applications.

We report on a technique that enables to fabricate three-dimensional (3D) metallic microstructures by means of two photon- induced metal-ion reduction. A femtosecond near-infrared laser is focused by a high-NA objective lens into a metal-ion aqueous solution. Due to the nonlinear nature of the two-photon absorption (TPA) process, metal-ions are directly reduced only at the focused spot. By scanning the laser beam spot in three dimensions, we can directly obtain arbitrary 3D metallic structures. To fabricate silver and gold structures, we use a 0.2-M aqueous solution of silver nitrate (AgNO₃) and a 0.24-M aqueous solution of tetra chloroauric acid (HAuCl₄), respectively. We demonstrate the fabrication of a continuous and electrically conductive silver wire whose minimum width is 400 nm. Electrical measurement shows that the resistivity of the fabricated silver wire is 5.30 × 10^-8 Ωm, which is only 3.3 times larger than that of bulk silver (1.62 × 10^-8 Ωm). We also discuss the resolution of our technique in terms of ions diffusion based on the Fick's first law and the mobility of metal-ions in aqueous solution. Moreover, the realization of a selfstanding 3D silver microstructures on the substrates are demonstrated. This method will become a promising technique for fabricating 3D plasmonic micro/nano structures with arbitrary shape.

We report a preliminary result of scanning probe nanofabrication using an AFM (atomic force microscopy) tip with assistance of femtosecond laser pulses to enhance fabrication capability. Illumination of the AFM tip with ultra-short light pulses induces a strong electric field between the tip and the metal surface, which allows removing metal atoms from the surface by means of field evaporation. Computer simulation reveals that the intended field evaporation is triggered even in air when the induced electric field reaches the level of a few volts per nanometer, which is low enough to avoid unwanted thermal damages on most metal surfaces. For experimental validation, a Ti:sapphire femtosecond pulse laser with 10 fs pulse duration at 800 nm center wavelength was used with a tip coated with gold to fabricate nano-size holes on a thin film gold surface. Experimental results demonstrate that fine holes with a diameter of less than ~10 nm can be successfully made with precise control of the intensity of femtosecond laser pulses.

We report on selective metal deposition over complex polymer structures formed by two-photon induced photopolymerization (TPP) technique. Periodic three-dimensional (3D) polymer micro/nanostructures are fabricated by means of a microlens array to produce multiple spots from a single-beam femtosecond laser amplified by a regenerative amplifier. The photopolymerizable resin and the glass substrate are chemically modified, and a pre-treatment with SnCl2 is applied before realizing a uniform silver coating by electroless plating. This preparation enables a selective deposition of small silver particles only on the polymer surface all over the sample and to avoid metal deposition on the substrate. Electrical measurements show the structures to be highly conductive with typical resistivities ρ approx. 10^-7 Ωm, only a few times larger than the value for bulk silver. By taking advantage of the high accuracy and arbitrary shape modeling of TPP fabrication, we can realize complex periodic and/or metallic micro-nanostructures which were so far out of reach. Thus, a straightforward application could be the realization of metamaterials. The processing efficiency of our technique is demonstrated with the fabrication of several large samples, created by more than 700 objects written in parallel and metallized with silver.

In this contribution, we demonstrate multi-photon femtosecond laser lithography for the fabrication and rapid prototyping of plasmonic components. Using this technology different dielectric and metallic SPP-structures can be fabricated in a low-cost and time-efficient way. Resolution limits of this technology will be discussed. Investigations of the optical properties of the fabricated SPP-structures by far-field leakage radiation microscopy will be reported.

Recently, fabrication of metal micro-pattern has attracted a great attention. For such purpose, site-selective activation is crucial for metal deposition on a substrate, and it can be achieved through lithography, chemical vapor deposition and micro-contact printing. Here, we propose to control the activation point three-dimensionally (3D) through two-photon absorption (TPA) polymerization method, which leads to 3D site-selective deposition. Two types of photopolymer were prepared for deposition control of metal through electroless plating method. One was a commercially available resin, which is typically inactive to metal deposition. Another was a modified resin containing suitable functional groups for metal adhesion. We created a 3D polymer structure consisting of those two components by localizing each resin through TPA method. The fabricated structures were immersed in an electroless plating solution of silver. The partially silver coated sample was observed by a scanning electron microscope after washing and desiccation. Metal microstructure supported with polymer can be realized by 3D site-selective metal deposition. Therefore, it is a useful technique for 3D aligned metallic microstructures without any contacts each other.

The continuing size reduction of integrated circuits to nano dimensions requires the development of advanced lithographic techniques. In order to obtain the desired feature sizes, it has become increasingly complex and high-cost to use the established methods of optical projection lithography at short optical wavelengths. Surface-plasmon polariton interference lithography (SPPIL) can provide a feasible way to achieve or approach the ultimate resolution for a certain wavelength without requiring complicated and expensive large numerical aperture optics. But it demands the fabrication of gratings with very fine period as a mask to realize contact printing, and the imaging quality is seriously dependent on the structure and materials of the mask, the illuminating light, photoresist, etc. So the optimization of the technological parameters is important to improve the imaging quality of nanolithography based on surface-plasmon polariton(SPP). In this paper, the simulation of near-field distribution of SPPIL is performed using Finite Difference Time Domain FDTD method, and the impacts of some technological conditions to the exposure field are analyzed including the polarization state and wavelength of the illuminating light, the periodicity, thickness and slit width of the mask, and so on. The simulation results show that, it is possible to fabricate good quality pattern with about 60nm features, with SPPIL using a 436nm-wavelength incident light.

A very large transmission, 20%, of light through a nano metallic slit bordered by both nano trenches and bumps has been demonstrated theoretically. The trenches bordering the nano slit, are used to excite free-space light into surface waves, while the bumps bordering the trenches are used to confine surface wave leakage. Over 50% of the escaping surface waves can be reclaimed by using a pair of bumps with a reflectivity larger than 99%. As a result, the transmission of a trench-surrounded slit bordered by a pair of bumps can be enhanced 1.5 fold.

In this paper we investigate the change of surface plasma (SP) resonance of a left-handed material (LHM) nano-slab. The intrinsic parameters of the LHM slab are suitable chose so that it has both negative permittivity and permeability in a frequency range of visible light. We calculate the attenuated total reflection (ATR) spectra of the LHM slab by use of the transfer matrix method. The spectra of different cases with various slab thickness and surrounding dielectrics of the LHM slab have been studied. The variations of SP resonance wavenumber and the corresponding resonance strength are discussed from the results of calculated ATR spectra.

The near-field and far-field optical properties of Sb-type near-field optical disk structures with different polarized situations are studied by finite-difference time-domain (FDTD) method. Localized surface plasmon enhancements are found around rough surface of Sb layers for TM polarized, but no near-field enhancement is found in cases with TE polarized incident waves. Far-field readout contrast signals of both TE and TM polarized situations show the superresolution capability, because evanescent signals of subwavelength recording marks are coupled to propagating waves by nanostructures (nano aperture or rough surface) in near-field active layer. Nevertheless, the contrast signals for TM illumination are higher than TE illumination due to localized surface plasmon enhancements. A simplified Fourier optics model is used to describe the relation between highly localized near-field distributions and enhanced resolution of far-field signals.

A nanometer-scale gap sensing technique based on surface plasmon resonance principle is presented. A simulation to the gap sensing technique and an experimental setup to verify the simulation results have both done in this study. For simulation, Fresnel's equation was used to derive the multilayer reflectivity of KR configuration of SPR devices. The results show that the resonance angle increased when the air gap, which was within half a wavelength, between the SPR device and the glass slide was decreased. For experiment, we measured the reflectivity versus incident angle. The results verify the theoretical prediction. Utilizing this novel surface plasmon resonance gap sensing technique, we have measured an air gap down to 100 nm. The technique is better than the other methods used in nanometer-scale gap measurements.