This PDF file contains the front matter associated with SPIE Proceedings Volume 8457, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Few/single molecule detection is of great importance in fields including biomedicine, safety and eco-pollution in relation to rare and dangerous chemicals. Superhydrophobic surfaces incorporated with the nanoplasmonic structure enable this device to overcome the diffusion limit of molecules dissolved in water with the concentration down to 10 attomolar. In this paper demonstrated the fabrication of hydrophobic surfaces using optical lithography/reactive ion etching and its application to overcome the diffusion limit. Various experiments such as contact angle measurements, SEM, fluorescence, Raman and FTIR absorption spectroscopy were performed which indicate that utilizing this device it could be possible to perform the measurements for the sample with extremely low dilution. The major application of this novel family of devices would be the early detection of tumors or other important pathologies, with incredible advances in medicine.

Cascaded optical field enhancement in coupled plasmonic nanostructures has attracted significant attention because of field enhancement factors that dramatically exceed those observed in isolated nanostructures. While previous studies demonstrated the existence of cascaded enhancement, little work has been done to identify the requirements for achieving maximum field enhancement. Here, we investigate cascaded field enhancement in silver nanosphere dimers as a function of volume ratio and center-to-center separation, and show the requirements for achieving the ultimate cascading limit in nanoparticle dimers. We observe field enhancements that are a factor 75 larger than observed in isolated silver nanoparticles.

A quantum treatment for surface plasmons is very useful. It allows to model effects like stimulated and spontaneous emission. So far, most of the research has been focused on semi-infinite metal boundaries for non-retarded surface plasmons. In this report, we use a second quantization scheme for retarded surface plasmons. The hydrodynamic model is used to model the electron density near metallic boundaries. The focus in this report is on circular cylinder shaped metal inclusions in a conventional dielectric host.

Frequency control of plasmon resonances is important for optical sensing applications such as Surface Enhanced Raman Spectroscopy. Prior studies that investigated substrate-based control of noble metal nanoparticle plasmon resonances mostly relied on metal substrates with organic or oxide spacer layers that provided a fixed resonance frequency after particle deposition. Here we present a new approach enabling continuous resonance tuning through controlled substrate anodization. Localized Surface Plasmon tuning of single gold nanoparticles on an Al film is observed in single-particle microscopy and spectroscopy experiments. Au nanoparticles (diameter 60 nm) are deposited on 100 nm thick Al films on silicon. Dark field microscopy reveals Au nanoparticles with a dipole moment perpendicular to the aluminum surface. Subsequently an Al2O3 film is formed with voltage controlled thickness through anodization of the particle coated sample. Spectroscopy on the same particles before and after various anodization steps reveal a consistent blue shift as the oxide thickness is increased. The observed trends in the scattering peak position are explained as a voltage controlled interaction between the nanoparticles and the substrate. The experimental findings are found to closely match numerical simulations. The effects of particle size variation and spacer layer dielectric functions are investigated numerically. The presented approach could provide a post-fabrication frequency tuning step in a wide range of plasmonic devices, could enable the investigation of the optical response of metal nanostructures in a precisely controlled local environment, and could form the basis of chemically stable frequency optimized sensors.

We study oscillations of a spaser driven by an external optical wave. When the frequency of the external field is shifted from the frequency of an autonomous spaser, the spaser exhibits stochastic oscillations at low field intensity. The plasmon oscillations lock to the frequency of the external field only when the field amplitude exceeds a threshold value. We find a region of external field amplitude and the frequency detuning (the Arnold tongue) for which the spaser becomes synchronized with the external wave. We obtain the conditions upon the amplitude and frequency of the external field (the curve of compensation) at which the spaser’s dipole moment oscillates with a phase shift of π relatively to the external wave. For these values of the amplitude and frequency, the loss in the metal nanoparticles within the spaser is exactly compensated for by the gain. It is expected that if these conditions are not satisfied, then due to loss or gain of energy, the amplitude of the wave travelling along the system of spasers either tends to the curve of compensation or leave the Arnold tongue. We also consider cooperative phenomena showing that in a chain of interacting spasers, depending on the values of the coupling constants, either all spasers oscillate in phase or a nonlinear autowave travels in the system. In the latter scenario, the traveling wave is harmonic, unlike excitations in other nonlinear systems. Due to the nonlinear nature of the system, any initial distribution of spaser states evolves into one of these steady states.

In this work, we investigated, both theoretically and experimentally, the saturable scattering in a single gold nanoparticle for the first time. In theoretical part, we used different models of the nonlinear properties to explain the nonlinear responses in gold material. In experimental part, multi-color confocal microscopy was used to observe the scattering of a single gold nanoparticle. As a result, by a resonant excitation, saturable scattering was observed with moderate excitation intensity (~10⁷ W/cm²); with even higher excitation intensity (>10⁹ W/cm²), reverse saturable scattering was observed, indicating the existence of higher order nonlinear properties. To completely comprehend the mechanism of this saturable scattering, we applied three kinds of excitation wavelengths (405nm, 532nm and 671nm) and four kinds of gold nanoparticle with different diameters (40nm, 50nm, 80nm and 100nm) to demonstrate the wavelength dependence and size dependence. Since the scattering of gold nanoparticles is significantly enhanced by localized surface plasmon resonance, we compared these dependencies with the spectral properties induced by LSPR and found that they match the spectra, revealing that the saturation is dominated by plasmon resonance. Besides, by fitting the dependencies, linear and nonlinear hyperpolarizability of a single gold nanoparticle were also deduced.

We demonstrate that the Fano resonances can be generated in a quasi-3D (Q3D) plasmonic nanostructure array fabricated on an indium tin oxide (ITO) coated glass substrate because of the interference between the broad plasmon modes of the gold nanodiscs and the narrow waveguide mode of the dielectric waveguide of the ITO layer. The finite-difference time-domain (FDTD) simulations were performed to investigate the far-field reflectance spectra and the near-field electric field distributions. The Q3D plasmonic nanostructure arrays were fabricated on ITO coated glass substrates via electron beam lithography (EBL) and the reflectance spectra were measured and compared to the simulation results. The effect of the Fano resonances on surface-enhanced Raman scattering (SERS) was studied. The results show that a strong enhancement can be achieved by tuning the narrow Fano resonance near the excitation wavelength and the broad plasmon resonance covering both the excitation and the Stokes Raman scattering wavelengths.

Leakage radiation spectroscopy of organic nanofibers composed of self-assembled organic molecules (para-Hexaphenylene, p-6P) deposited on a thin (40-60 nm) Ag film has been performed in the spectral range 420-675 nm which overlaps with the nanofiber photoluminescence band. Using a soft transfer technqiue, domains of mutually parallel oriented organic nanofibers were initially grown under high-vacuum conditions by molecularbeam epitaxy onto a cleaved muscovite mica substrate and afterwards transferred onto a silver film prepared on the glass carrier. The sample placed on a flat side of a hemisphere prism with an index matching liquid was illuminated by either a He-Cd 325 nm laser or by white light from a bulb. In the case of laser excitation two orthogonal linear polarizations and two different configurations of p-6P nanofibers were applied, both parallel and perpendicular to the plane of detection. The leakage radiation was observed on the opposite side of the Ag film at the phase matching angle. The spectrally resolved intensity of the scattered radiation has been measured as a function of scattering angle at normally incident light. The spectrum contains a distinct peak at an wavelength dependent angle above the critical angle. By analyzing this dispersion curve one can argue that it originates from the interaction between the nanofiber excitons and surface plasmon polaritons of the metal film.

Ultrashort extreme-ultraviolet (EUV) light pulses are an important tool for time-resolved pump-probe spectroscopy to investigate the ultrafast dynamics of electrons in atoms and molecules. Among several methods available to generate ultrashort EUV light pulses, the nonlinear frequency upconversion process of high-harmonic generation (HHG) draws attention as it is capable of producing coherent EUV pulses with precise control of burst timing with respect to the driving near-infrared (NIR) femtosecond laser. In this report, we present and discuss our recent experimental data obtained by the plasmon-driven HHG method that generate EUV radiation by means of plasmonic nano-focusing of NIR femtosecond pulses. For experiment, metallic waveguides having a tapered hole of funnel shape inside were fabricated by adopting the focused-ion-beam process on a micro-cantilever substrate. The plasmonic field formed within the funnelwaveguides being coupled with the incident femtosecond pulse permitted intensity enhancement by a factor of ~350, which creates a hot spot of sub-wavelength size with intensities strong enough for HHG. Experimental results showed that with injection of noble gases into the funnel-waveguides, EUV radiation is generated up to wavelengths of 32 nm and 29.6 nm from Ar and Ne gas atoms, respectively. Further, it was observed that lower-order EUV harmonics are cut off in the HHG spectra by the tiny exit aperture of the funnel-waveguide.

The excitation of surface plasmons in metallic nanostructures by resonant ultrashort femtosecond light pulses produces interesting phenomena such as optical field nanolocalization, nanoscale electric field enhancement and ultrafast sub-femtosecond beating of the plasmon eigenmodes. Nonlinear two-photon photoemission electron microscopy has proven to be a powerful tool for spatiotemporal characterization of such effects on the nanoscale below the optical diffraction limit. As a step toward using intense, few-cycle 4 femtosecond laser pulses to excite and control surface plasmons, we report on the multiphoton-photoemission electron microscopy experiments on lithographically-fabricated gold nanostructures excited by these few-cycle laser pulses. In addition, the effects of the shape and size of silver plasmonic structures, as well as the polarization of the excitation source are examined in the two-photon photoemission induced by picosecond laser pulses. Potential approaches toward spatiotemporal control of lightfield nanolocalization are described.

Spin-symmetry breaking in nanoscale structures caused by spin-orbit interaction, leading to a new branch in optics – spinoptics is presented. The spin-based effects offer an unprecedented ability to control light and its polarization state in nanometer-scale optical devices, thereby facilitating a variety of applications related to nano-photonics. The direct observation of optical spin-Hall effect that appears when a wave carrying spin angular momentum (AM) interacts with plasmonic nanostructures is introduced. A plasmonic nanostructure exhibits a crucial role of an AM selection rule in a light-surface plasmon scattering process. A spin-dependent dispersion splitting was obtained in a structure consisting of a coupled thermal antenna array. The observed effects inspire one to investigate other spin-based plasmonic effects and to propose a new generation of optical elements for nano-photonic applications.

The comprehensive understanding of the excitation and propagation of surface plasmons (SPs) on metallic nanowires (NWs) is essential for potential applications of these materials as nanoscale optical waveguides. Combining theory and different experimental methods, we did intensive study on the excitation and propagation of SP modes in crystal Ag nanowires. We found the excitation of NW SP modes is strongly affected by the excitation configuration. When an optically “thick” NW is radiated at the end of the NW, several SP modes could be excited simultaneously with appropriate incident polarization. If the NW is in the medium of uniform refractive index, the coherent superposition of these SP modes generates chiral SPs in single NW, and the handedness of the chiral SPs can be controlled by the input polarization angle. When we use a near field scanning optical fiber tip to excite the SPs on metallic nanowires from the middle of the NW, we also found multiple SP modes in the NWs can be excited through polarization selective near field interaction. The excitation mechanism of the tip-induced SP propagation is quite different from the previous wire-endlaunching scheme. We found the input coupling efficiency is modulated by Fabry-Pérot interferences in the near field coupling case.

We present a fabrication method of gold nanorod/ polymer composite microstructures by means of a femtosecond near-infrared laser light. The mechanism of this method is based on a cooperation of two optical reactions; two-photon polymerization (TPP) reaction only at the surface of gold nanorods, and optical accumulation of gold nanorods in photo-polymerizable resin. Gold nanorods were mass-produced by seed mediated growth method, and were mono-dispersed in photo-resin. The wavelength of the laser light was tuned resonant to two-photon absorption of the photo-resin, and also close to a longitudinal local surface plasmon resonance (LSPR) mode of the gold nanorods. The laser light excited LSPR onto gold nanorods, resulting in the formation of thin polymer layer only at their surface through TPP. Concurrently occurring optical accumulation of gold nanorods by continuous irradiation of laser light, gold nanorods got together into focus spot. The TPP layer at the surface of gold nanorods worked as a glue to stick one another for forming their aggregated structure in micro/nano scale. By controlling the intensity and the exposure time of laser light, an optimal condition was found to induce dominant polymerization without any thermal damages. The scanning of the focus spot makes it possible to create arbitrary micro/nano structures. This method has a potential to create plasmonic optical materials by controlling the alignment of gold nanorods.

The scattering properties of a plasmonic array can be reinforced by placing the array near a planar reflector. Finite- Difference-Time-Domain (FDTD) simulations have been used to demonstrate the key design challenge of modulating the electric field that drives the plasmonic scattering, by varying the distance of a single Ag nanodisc from a Ag reflector. We show that the thickness of the dielectric separation layer plays a critical role in determining the spectral characteristics and the intensity of the power scattered by a Ag nanodisc near a reflector. A possible application of the designed structure as a plasmonic light-trap for thin Si solar cells is also experimentally demonstrated. Electron-beam lithography has been used to fabricate a pseudo-random array of 150nm plasmonic Ag nanodiscs on SiO₂ on a Ag reflector substrate. The plasmonic reflector shows a high diffuse reflectance of ~54% in the near-infrared, near-bandgap 600-900nm wavelength region for thin Si solar cells, with a low broadband absorption loss of ~18%. Wavelength-angle resolved scattering measurements indicate an angular scattering range between 20° to 80° with maximum intensity of the scattered power in the 20° to 60° angular range.

We have demonstrated the surface plasmon-polariton interference using a long-range surface plasmon-polariton waveguide coupler. A clear interference fringe with the visibility of 87 % was observed. The coupling ratio of the waveguide coupler was estimated to be 64:36 by two-photon interference experiments.

We fabricated a plasmonic racetrack resonator with a trench structure, evaluated it at visible wavelengths, and observed its operation at these wavelengths. Trench channel plasmon polaritons were stored in the racetrack resonator when incident light irradiated the input port. The plasmonic racetrack resonator with a trench struc- ture can be fabricated in only a few steps, and the resulting increase in the coupling coefficient has potential applications in optical integrated circuits.

Optical antennas and passive resonant structures, as frequency selective surfaces, configure a new kind of optical systems that can be classified as belonging to the resonant optics area. Typical antenna-coupled detectors using microbolometers as transducers have included materials with the largest temperature coefficient of resistance (TCR) value. These materials are located at the feed point of the antenna where the electric current is the largest and the Joule effect dissipates the best. At the same time, the signal delivered to the external circuit is also depending on the resistivity value. This two-material configuration requires al least two e-beam fabrication steps. Although the resistivity values of metals changes substantially, the actual range of TCR values for most of metals is quite narrow. In this contribution we analyze how the choice of the material involved in the fabrication of resonant structures may enhance the bolometric effect. This analysis is made taking into account the electromagnetic interaction of light with the resonant element. The generated heat changes temperature and this variation produces the signal. Finite element package Comsol has been used to properly simulate the situation and predict the effect of changing the fabrication to an unique material, simplifying the manufacturing. Besides, the performance of the structure is depending on the used material.

We theoretically investigate compact plasmonic coupler based on metal nanopillar over silicon on insulator substrate demonstrating routing of light at nanoscale. Proposed geometry demonstrates strong mode confinement, allows sharp bends with low loss and easy integration on chip circuitry. The coupler is optimized for visible regime and can be tuned for specific wavelengths. Plasmonic transverse magnetic (TM) modes are observed and examined using finite difference time domain (FDTD) computations. Coupling length (Lc) and gap width (Wc) for the nanopillar assisted four-port plasmonic coupling structure is optimized to give enhanced efficiency. The structure renders subwavelength light manipulation overcoming conventional photonics with applications in plasmonic circuitry for nanoscale guidance of light in data transmission, integrated chip design etc.

In this paper we describe the fabrication of a periodic, two-dimensional arrangement of gold square patches on a Silicon substrate, and highlight technological limitations due to the roughness of the metal layer. Scanning Electron Microscope (SEM) and Atomic Force Microscope analyses are also reported showing that the geometrical parameters obtained are almost identical to the nominal parameters of the simulated structure. The device is functionalized by means of a conjugated rigid thiol forming a very dense, closely packed, reproducible 18 Å–thick, self-assembled monolayer. The nonlinear response of the 2D array is characterized by means of a micro-Raman spectrometer and it is compared with a conventional plasmonic platform consisting of a gold nano-particles ensemble on Silicon substrate, revealing a dramatic improvement in the Raman signal. The SERS response is empirically investigated using a laser source operating in the visible range at 633 nm. SERS mapping and estimation of the provided SERS enhancement factor (EF) are carried out to evaluate their effectiveness, stability and reproducibility as SERS substrate. Moreover, we take advantage of the simple geometry of this 2D array to investigate the dependence of the SERS response on the number of total illuminated nano-patches.

Ripples on silicon have been fabricated by femtosecond laser ablation to minimize Si removal and to achieve a flat (not a groove-like) coverage of extended millimeter size areas for nano-/micro-fluidic applications. Such flat ripple-covered regions were found to control flow and wetting properties of water. Depending on orientation of ripples the flow speed of a 1 µl water droplet can be changed from 1.6 to 9.1 mm/s. Gold-coated ripples on sapphire are demonstrated as an excellent SERS substrate with more than one order-of-magnitude larger sensitivity and superior reproducibility a,.., compared to the commercial SER.S substrates; SERS signal on the ripples was more than 15 times higher and more than 2 times more uniform as compared to Klarite substrate at 633 mn excitation wavelength. It was shown that ripples can also be fabricated on thin transparent conducting indium tin oxide (ITO) coatings of 45 mn thickness. The electrical resistance can be controlled by orientation and area fraction of ripples. Applications on miniaturized heaters for incubation and micro-chemistry chambers on lab-on-chip and electrowetting are discussed along with potential applications in orientational flows, self-assembly of micro-chips, and sensing.

Considerable magneto-optical activity has been observed in aqueous solutions of colloidal noble metal nanoparticles (Au and Ag, 2–50 nm in diameter) in a magnetic field as low as 0.5 T parallel to the propagation of the incident light exciting localized surface plasmons in the nanoparticles. The magnetic circular dichroism (MCD) spectra show pronounced Zeeman splitting in the plasmon absorption bands. The observed magneto-optical effects is due to the enhancement of the magnetic Lorentz force for localized surface plasmons in resonantly excited strongly polarizable Ag and Au nanoparticles. The magnitude and the spectral position of the MCD signal depend on the contribution of scattering and absorption components in the extinction spectra of nanoparticles. Addition of pyridine into the colloidal solution of silver nanoparticles causes aggregation of nanoparticles and the appearance of a characteristic intense long-wavelength band in the extinction spectrum. The MCD spectrum also shows signals from short- and long-wavelength components. The possible method for MCD biosensing based on controlled aggregation of plasmonic nanoparticles in the presence of analyte followed by differential MCD detection in the long-wavelength region is discussed.

Nowadays, bringing photovoltaics to the market is mainly limited by high cost of electricity produced by the photovoltaic solar cell. Thin-film photovoltaics offers the potential for a significant cost reduction compared to traditional photovoltaics. However, the performance of thin-film solar cells is generally limited by poor light absorption. We propose an ultrathin-film silicon solar cell configuration based on SOI structure, where the light absorption is enhanced by use of plasmonic nanostructures. By placing a one-dimensional plasmonic nanograting on the bottom of the solar cell, the generated photocurrent for a 200 nm-thickness crystalline silicon solar cell can be enhanced by 90% in the considered wavelength range. These results are paving a promising way for the realization of high-efficiency thin-film solar cells.

We have investigated optical characteristics of silicon nanowire (Si NW) on Al disk arrays using the finite-difference time-domain (FDTD) simulations. Without the Al disk, the Si NW arrays alone exhibit strong absorption peaks, originated from guided mode resonance. The arrays of SiNW with Al disk possess additional broad peaks, at slightly larger wavelengths than those of the resonant guided mode peaks. The FDTD simulations show formation of concentrated electromagnetic field at the Si NW/Al interface, indicating excitation of localized surface plasmons. These results suggest that bottom-contact electrodes can work as means to enhance the optical absorption of the Si NWs as well as to collect carriers in Si NW-based optoelectronic devices.

We experimentally investigated Zinc oxide (ZnO) nanowires (NWs) on flat Si substrate and ZnO NWs on Au nanoislands attached on a Si substrate via hydrothermal technique, pursuing surface enhanced Raman scattering (SERS). Au nanoislands were formed by thermal annealing of a Au thin film deposited on Si substrate. ZnO NWs were then grown on two types of substrates (with and without Au nanoislands) and thermally annealed together. During the thermal annealing process, the ZnO NWs were coupled to Au nanoislands. After the thermal annealing, strong SERS enhancement was observed of ZnO NWs on Au nanoislands. Over 30 times enhancement in SERS was found when the initial Au layer thickness was 40 nm.

It is shown that fork-shaped plasmonic gratings can display a hybrid mode that features both plasmonic mode (TMmode) and dielectric mode (TE-mode) characteristics with wide range of tunable group velocities. A dielectric gap is introduced in the middle of metallic grating and it is found that this gap plays an important role in controlling the TE-TM mode coupling. By controlling the polarization angle we can switch from plasmonic mode to dielectric mode. Thus, a new scheme for manipulating the optical confinement by using a polarizer is realized. (see Figure) We can combine the plasmonic mode and dielectric mode to reduce the intrinsic loss of Plasmon-polariton due to the free-carrier absorption in the conducting material with the same degree of confinement. The fork structure provides an easier way to control the group velocity in a wide range. The dispersion relations were calculated by using Rigorous Coupled Wave Analysis. We obtain tunable group velocities ranging from 0.2c to almost zero (i.e. achieving localized Surface Plasmon-polariton) and from 0.05c to 0.3c by varying the pillar and dielectric (made of Si₃N₄) thicknesses respectively. This fork structure is expected to have applications in surface plasmon polariton (SPP) mixed with guided-mode based optical devices, such as optical buffering, hybrid waveguides, splitters and lasers and especially for applications requiring slow light propagation.

We report that unique properties of long-range surface plasmon polaritons (LR SPP) allow one to produce optical components with very wide tuning range using small variations in the refractive index of the dielectric layer. Our filter is based on integration of a thin metal film between two dielectrics with dissimilar refractive index dispersion. In this configuration, the filter only has low insertion loss at a wavelength for which the refractive indices of the top and bottom dielectrics are the same, leading to a bandpass filter. As a proof-of-principle demonstration, we present operation of LR-SPP- based bandpass optical filters with refractive index matching fluids on an Au/SiO₂ surface in which a 0.004 variation in the refractive index of the top dielectric translates into 210nm of bandpass tuning at telecom wavelengths. To make a more practical solid-state device, thermo-optic polymer can be used as a top dielectric and we expect that only 8°C of temperature variation translates into 200nm. The tuning mechanism proposed here may be used to create monolithic filters with tuning range spanning over more than an optical octave, compact and widely-tunable laser systems, multi-spectral imagers, and other plasmonic components with broadly-tunable optical response.

Electromagnetic radiation is attenuated by a metal grid disposed on a substrate. The magnitude of extinction is a combination of the total scattering and surface plasmon absorption, as predicted by the Mie theory adapted to the case at hand. Experimental measurements conducted over a wide wavelength range using a metal grid on a sapphire window support the calculations. We analyzed the electric field generated in the wire mesh by the Drude-Lorentz theory. While the analysis and data show that the attenuation across a window covered by a wire mesh consists of a combination of the Fresnel and Mie losses, a considerable plasmon field is generated in the wire. Further it is shown that under visible illumination the metal grid generates enough electrical filed to substantially elevate the window temperature.

We report far-field optical extinction spectra of linear chains of gold and silver nanocylinders with interparticle separations close to the particles' surface plasmon resonance (SPR) wavelength. The spectra reveal a typical pattern of dipole-like and quadrupole SPR peaks and additional non-SPR peaks. We rationalize the extra peaks by constructive interference of the scattered and incident electromagnetic fields.

Mid-infrared photodetectors are the subject of many research efforts within the last two decades for enhancing their operating parameters such as temperature stability, detectivity and quantum efficiency. This is due to their wide range of applications like biosensing, night vision, and short range communication. However, mid-infrared photons have much smaller energy compared with the band gap energy of well known semiconductors including III-V and II-VI families. One way to overcome this problem is to utilizing quantum confinement effects by absorbing a photon through the intersubband transition of a conduction electron or valance hole. Fabricating devices at the nanoscale size to achieve quantum confinement is costly and imposes limitations for further device preparation. In addition, the optical properties of quantum confined devices are sensitive to nanoscale geometrical parameters which make them vulnerable to fabrication imperfections. The other approach of detecting mid-infrared light is by exploiting the non-degenerate two photon absorption process (TPA). Two photons with different energies can be absorbed simultaneously by a semiconductor with the band gap energy less than the overall energy of two photons. Thus, a mid-infrared photon as the signal can be detected by a bulk semiconductor with much larger band gap energy when a near-infrared photon as the gate assists the absorption process through TPA.

We report our results on arrays of transparent metal coated wedges for plasmonic nanofocusing. FIB milling and chemical etching were used for the fabrication. FEM simulations were used to design the system. The design, fabrication and characterization of wedge structures are presented. The structure shows plasmonic properties in the optical spectral range, with excitation and propagation of surface plasmon polaritons at the wedge tip. The particular designs proposed allow the condensation of plasmonic waves at the wedge tips leading to the nanofocusing effects.

In this paper, a design of Planar Metamaterial Optical Antenna based on split ring resonance (SRR) structure is reported. The design exploits the special property of the metals and metamaterials. Metal acts as strongly coupled Plasmon in nano-scale range when operated at optical frequency. Planar metamaterial exhibits its optical properties from the structure rather than the composition. The structure of planar metamaterial antenna is tailored in such a way that it will yield an antenna of high directivity and enhanced intensity response in the optical frequency regime.

Nanobump structures are fabricated on the gold thin film by femtosecond laser direct writing (fs-LDW) technique. The height and diameter of the gold nanobump are about 30nm, and 400 nm, respectively. The scattering light of surface plasmon wave radiated from a nanobump is observed using a total internal reflection microscopy. A quarter-circle structure composed of nanobumps is designed and produced to manipulate scattering light into specific pattern: The focusing and diverging of the quarter circular structure in three dimensional space are demonstrated. The polarization properties of focusing spot are also examined.

The mesoscopic effect of spectral modulation occurring due to the interference of two photonic fiber modes filtered out by a metal-coated SNOM tip is used to observe the surface plasmon polariton (SPP) excitation in SNOM tips. In a spectrum of the broadband light transmitted by a SNOM tip a region of highly regular spectral modulation can be found, indicating the spectral interval in which only two photonic modes (apparently HE₁₁ and TM₀₁) are transmitted with significant and comparable amplitudes. The modulation period yields the value of optical path difference (OPD) for this pair of modes. Due to the multimode fiber’s inherent modal dispersion, this OPD value depends linearly on the fiber tail length l. An additional contribution to OPD can be generated in a metal-coated SNOM tip due to a mode-dependent photon-plasmon coupling strength resulting in generation of SPPs with different propagation velocities. For an Al-coated 200 nm SNOM tip spectra of transmitted light have been registered for ten different l values. An extrapolation of the linear OPD (l) dependence to l=0 yields a significant residual OPD value, indicating according to our theoretical considerations a mode-selective SPP excitation in the metal-coated tip. The modal dispersion is shown to switch its sign in the SNOM tip. First results of analogous experiments with an Al-coated 150 nm SNOM tip confirm our conclusions.

The synthesis and study of optical properties of copper nanoparticles are of great interest since they are applicable to different areas such as catalysis, lubrication, conductive thin films and nanofluids. Their optical properties are governed by the characteristics of the dielectric function of the metal, its size and environment. The study of the dielectric function with radius is carried out through the contribution of free and bound electrons. The first one is corrected for size using the modification of the damping constant. The second one takes into consideration the contribution of the interband transitions from the d-band to the conduction band, considering the larger spacing between electronic energy levels as the particle decreases in size below 2 nm. Taking into account these specific modifications, it was possible to fit the bulk complex dielectric function, and consequently, determine optical parameters and band energy values such as the coefficient for bound electron contribution Q_bulk = 2 x 10²⁴, gap energy E_g = 1.95 eV, Fermi energy E_F = 2.15 eV and damping constant for bound electrons γ_b = 1.15 x 10¹⁴ Hz. The fit of the experimental extinction spectra of the colloidal suspensions obtained by 500 μJ ultrashort pulse laser ablation of solid target in water and acetone, reveals that the nanometric and subnanometric particles have a Cu- Cu₂O structure due to an oxidation reaction during the fabrication. The results were compared with those obtained by AFM, observing a very good agreement between the two techniques, showing that Optical Extinction Spectroscopy (OES) is a good complementary technique to standard electron microscopy.

A device consisting of a disk-shaped, Moiré-type plasmonic cavity placed inside a plasmonic crystal cavity, with a 250 nm polymethyl-methacrylate (PMMA) film over the cavities is analyzed by 3D finite-difference time domain (FDTD). Both cavities can be fabricated by Focus Ion Beam, and the waveguide and the Moiré cavity contour can be defined by one-step lithographic process. The device is characterized by calculating the cavity spectrum, the reflection and the radiation spectra and the electric field intensity distribution. It was verified that the transverse-magnetic (TM) input mode generates surface plasmon polaritons (SPP) at the PMMA/gold interface that excites localized surface plasmon polariton on the Moiré cavity, that, in turn, generates reflected waves back to the waveguide and diffracted radiation. Also, the lack of plasmonic crystal bandgap permits the evanescent coupling of Bloch waves to the plasmonic crystal. The high electric field generated by the LSPP on the Moiré surface, and by the Bloch waves at the borders of the plasmonic crystal holes, contributes to the fluorescence of molecules dissolved in the PMMA film. The radiated fluorescence can be detected by a lensed fiber placed above the Moiré surface, and the reflected signal can be detected at the output.

This study numerically and experimentally demonstrates the enhancement of phase detection sensitivity of a gratingcoupled surface plasmon resonance (GCSPR) sensor by using incident light at a nonzero azimuth angle. Phase detection measurements were performed using an electro-optic heterodyne interferometer. The experimental results show that when the GCSPR sensor was rotated azimuthally by 0° and 58°, the phase detection sensitivities were approximately 3.2x10^-7 RIU and 5.5x10^-8 RIU, respectively. The nonzero azimuth angle was found to enhance the sensor sensitivity by a factor of 5.87 relative to the zero azimuth angle

We present a novel theoretical approximation for predicting the enhanced optical transmission properties through a periodic array of subwavelength square apertures in perforated metal films. We show that a Fabry-Perot resonance occurs in an effective resonant cavity whose dimensions are determined by the apertures' geometry and the decay lengths of the associated evanescent diffracted modes. This model demonstrates strong agreement to simulated results, and can be used to rapidly and efficiently design aperture arrays with specific transmission properties.

The spectral radiative properties of coherent thermal emission in the mid- and far-IR from two metal-semiconductor resonating structures were demonstrated experimentally. Using an efficient implementation of Rigorous Coupled-Wave Analysis, a truncated resonator was designed to selectively emit at mid-IR and far-IR wavelengths. A High Impulse Power Magnetron Sputtering deposition technique was used to fabricate two Ag-Ge-Ag resonating structures with layer thicknesses of 6-240-160 nm for one sample and 6-700-200 nm for the other. Reflectance measurements demonstrated spectrally selective absorption at the designed mid- and far-IR wavelengths whose general behavior was largely unaffected by a wide range of incident angles. Further, radiance measurements were taken at various high temperatures, up to 601 K, where spectrally selective emission was achieved through wave interference effects due to thermally excited surface waves. From these radiance measurements, spectral emittance was directly derived and compared to the emittance inferred from reflectance measurements. It was established that inferring emittance through Kirchhoff’s law can help to approximate the expected emission from a structure, but it is not an exact method of determining the actual emittance of a thermal source at higher temperatures due to the temperature dependence of material parameters.

Conducting nanoparticles with plasmon resonances create local, nanoscopic field enhancements that boost an analyte molecule’s surface-averaged Raman scattering cross-section orders of magnitude above the bulk Raman cross-section by an amount known as the enhancement factor (EF). Demonstrations of single-molecule sensitivity with EF ~ 10¹³ have been reported from small “hot spots” (e.g., regions of enhanced electromagnetic near fields) on specialized substrates, but realistic chemical sensing requires high average EF over large substrates for practical sampling.¹ By using simple wet chemical methods, NSRDEC scientists have fabricated large-area arrays of novel, highly conducting, anisotropic Ag and Al nanoparticles. The nanoparticles adhere to an ultrathin layer of poly-4(vinyl pyridine), and are anchored by submicron coating of poly-methyl methacrylate on glass and SiO₂-coated Si substrates. The average interparticle spacing is determined by the dilution of the nanoparticle-water suspension. We present surface-enhanced Raman spectroscopy (SERS), spectrophotometry, and microscopy data from these nanoparticle arrays, model this data and the nanoscopic field enhancement, and determine the SERS EF. We compare the observed absorption resonances and SERS EF with those predicted by finite difference time domain modeling of the nanoscale fields and optical properties, and find good agreement between measured and calculated reflectivity, achieving EF ~ 10⁶ for benzenethiol adsorbed onto a monolayer array of 120 nm Ag nanoparticles over an area of ~ 0.5 cm². We discuss a way forward to increase SERS EF to 10⁷ with large-area samples assembled using chemical methods, by using spiky Ag “nano-urchins” with very large predicted field enhancements.

A novel plasmonic surface is evaluated as a potential surface for surface enhanced Raman scattering (SERS) experiments. This paper examines the electromagnetic response of an array of gold triangles commonly used for surface enhanced Raman scattering (SERS) with a finite element simulator, and then compares those results with the theoretical performance of a novel surface described herein. The gold triangle array modeled as a standard SERS surface could be fabricated using nanosphere lithography [1]. The new design introduced in this paper utilizes a strongly tapered nanowell shape, which is etched out of a gold/alumina multilayer stack. The nanowell void creates a series of resonators stacked on top of one another, with each metal/insulator/metal combination representing one resonator. Resonators with different void radii, have different refractive indices. Therefore, the taper of the nanowell defines the vertical refractive index gradient, and the taper in this paper was chosen to span both positive and negative refractive indices within the multilayer stack. The tapered nanowell design is shown to have a very strong response, and displays a unique stability with respect to disorder within the array.

A hybrid metal photonic crystal based nanostructured cavity and waveguide for the sub-wavelength confinement of light is proposed and it is shown that a bottom reflector is vital for the vertical emission from a silicon (Si) photonic crystal (PC) nanocavity. A photonic crystal slab of Si (ε_d=11.56 or n_d=3.4) with air holes and metal as an underlying substrate is chosen and three dimensional (3D) photonic bandgap for structure is calculated with plane wave expansion (PWE) method. Using finite difference time domain (FDTD) method, the transmission of a cavity mode as a function of Photonic crystal slab thickness is calculated and it is observed that the transmission increases with the increase in slab thickness at wavelength, λ = 1.55μm. Also, transverse electric field profiles (Ey) of the cavity mode has been shown and quality factor are calculated for the cavity and possible application in the area of PC light based emitters such as plasmonic lasers and single photon source is assessed.

Extraordinary transmission of surface plasmonic (SP) structures has been widely studied but lacking is a focus on the off-normal dependency of the resonant modes and how this affects the transmission spectrum. The measurements of offnormal spectral transmission for a SP structure were compared to finite-difference time-domain simulations. The SP sample is a gold/titanium thin film (50 nm) with a 2D square array of circular holes deposited on 1 μm of highly ndoped, n=2e18cm^-3, gallium-arsenide (GaAs) upon a semi-insulating GaAs substrate. Spectral transmission measurements were taken for wavelengths from 2-12μm, incident elevation and azimuthal angles of θ=0°, 20° and 40°, and φ=0° and 45°, respectively, with linearly polarized and un-polarized light. The first and second-order surface plasmon modes and their dependency on θ, φ, polarization and the grating momentum vector were identified. The measurements and simulations corroborate the theoretical analysis, giving a closed-form solution to the spectral location of lower-order modes. For off-normal incidence in a plane parallel to the array periodicity (φ=0°), the (1,0) mode as defined for p-polarization splits while the (0,1) mode as defined for s-polarization, remains essentially un-changed for all θ. For φ=45° incidence, both polarizations split the modes. Full polarimetric spectral transmission was both measured and simulated, giving a Mueller matrix representation of the spectral transmission of the SP structure at θ=0° and 20° and φ=0° and 45°, demonstrating that this structure is moderately depolarizing when resonant. The results show the dependence on incident angle and polarization of the extraordinary transmission of SP structures.

We investigate the long-range coupling of individual atoms coupled to plasmon modes of metallic nanostructures. Placing a pair of emitters along a thin metallic wire, we observe a strong, wire- mediated long-range interaction between the emitters. As a result, super- and subradiance can occur over distances large compared to the resonant wavelength. The states with enhanced or suppressed decay rate are the symmetric or anti-symmetric single-excitation states. Coupling more atoms to a wire network with a nontrivial coupling topology leads to interesting entangled subradiant states of the system. A similar long-range superradiance effect can be observed when two emitters are coupled by a metamaterial slab (also known as a perfect lens) having a refractive index n=-1. Besides the modification of decay rates, dipole-dipole shifts enter due to the plasmon-mediated interaction. Based on the superradiance effect, we propose setups for building a two-qubit quantum phase gate for quantum emitters coupled by a nanowire and a perfect lens, respectively, where the qubits are strongly interacting and individually addressable at the same time.

We experimentally demonstrate the possibility to implement an optical bio-sensing platform based on the shift of the plasmonic band edge of a 2D-periodic metal grating. Several 2D arrangements of square gold patches on a silicon substrate were fabricated using electron beam lithography and then optically characterized in reflection. We show that the presence of a small quantity of analyte, i.e. isopropyl alcohol, deposited on the sensor surface causes a dramatic red shift of the plasmonic band edge associated with the leaky surface mode of the grating/analyte interface, reaching sensitivity values of ~650nm/RIU. At the same time, dark field microscopy measurements show that the spectral shift of the plasmonic band edge may also be detected by observing a change in the color of the diffracted field. Calculations of both the spectral shift and the diffracted spectra variations match the experimental results very well, providing an efficient mean for the design of sensing platforms based on color observation.

In this paper, the near field distribution patterns excited from half spiral nanoslits and gratings are investigated. The various near field distribution patterns observed are due to the interference of propagating surface plasmon emerging from the nanoslits or gratings. The half spiral nanoslits are incident with left and right-handed circular polarization. The resulting focal spots are found at different positions for left (LHC) and right-handed circular (RHC) polarizations. This is due to the change in phase difference of propagating surface plasmon waves emerging from the nanoslit when excited by different circular polarizations. The distance between the focal spots for left and right-handed polarizations is λ_spp/2. In addition, the half spiral nanoslit is also illuminated with linear polarization in different rotational angles. This paper also includes the near field distributions that result from the interference of surface plasmon polariton fields with partial spiral shape. It is believed that these interesting field patterns due to different arrangements of nanoslits could be used for trapping molecules, near field imaging and sensing.

Laser cooling of materials has been one of the important topics of photonic research during recent years. This is due to the compactness, lack of vibration, and integratibility of this method. Although laser refrigeration has been achieved in rare earth doped glass, no net cooling of semiconductors has been observed yet. The main challenge in this regard is the photon trapping inside the semiconductors, due to its high refractive index, which prevents the extraction of the energy from the material. Various methods have been proposed to overcome photon trapping but they are either not feasible or introduce surface defects. Surface defects increase the surface recombination which absorbs some portion of the photoluminescence and converts it to heat. We exploit the surface plasmons produced in silver nanoparticles to scatter the PL and make the extraction efficiency significantly higher without increasing the surface recombination. This is also important in the semiconductor lighting industry and also for enhancing the performance of solar cells by coupling the sunlight into the higher index absorbing region. Finite difference time domain simulations were used to find the total power extraction efficiency of the silver nanoparticles. It is also proposed for the first time to use the silver nanoparticles as mask for dry etching. The results for both etched and unetched cases were compared with each other. We also refer to a method of silver nanoparticle fabrication which is easy to apply to all kinds of cooling targets and is relatively cheaper than deposition of complex anti-reflective coatings.

A study of a generic multishell cloaking system that conceals an object from incident electromagnetic radiation regardless of the object shape and/or material (optical) properties is presented. Transparency conditions based on zero permittivity materials for both cylindrically and spherically symmetric systems are derived. It has been shown that zero permittivity material shells can be realized using noble metals. In addition, we proposed a zero-index lowloss tunable shell design based on metal-dielectric composite material to realize the cloak. Our results show that the proposed design can achieve cloaking across the entire optical spectral range and can decrease the scattering-cross section by a factor of up to 10³. Furthermore, a full wave analysis is performed showing the independence of cloak performance on the object shape and material properties. The proposed approach toward clocking does not require optical magnetism and underline the importance of zero index materials for achieving electromagnetic invisibility.

Active resonance tuning is highly desired for the applications of plasmonic structures, such as optical switches and surface enhanced Raman substrates. In this paper, we demonstrate the active tunable plasmonic structures, which composed of monolayer arrays of metallic semishells with dielectric cores on stretchable elastic substrates. These composite structures support Bragg-type surface plasmon resonances whose frequencies are sensitive to the arrangement of the metallic semishells. Under uniaxial stretching, the lattice symmetry of these plasmonic structures can be reconfigured from hexagonal to monoclinic lattice, leading to not only large but also polarization-dependent shifts of the resonance frequency. The experimental results are supported by the numerical simulations. Our structures fabricated using simple and inexpensive self-assembly and lift-transfer techniques can open up applications of the stretch-tunable plasmonic structures in sensing, switching, and filtering.

Magnetoplasmonics merges plasmonics and magnetism, providing ways to control the surface plasmon propagation but also to control and probe the magnetism of materials. We present an analysis of the optical properties of magnetic cavity consisting of a magnetic dielectric between two sheets of non-magnetic metal. We find that the field distribution of the plasmonic modes inside the cavity is strongly dependent on the magnetisation. The very different field distributions of the modes, depending on the magnetisation direction of the dielectric, should allow interesting possibilities for future magnetic control of the coupling to far- field radiation.