This PDF contains the front matter associated with SPIE Proceedings Volume 6641, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Subwavelength hole arrays in metal films have the potential to exhibit narrow and high refractive index (RI) sensitive transmission features. We have previously demonstrated that such features can arise from the coupling between Wood anomalies (WAs) and surface Plasmon polaritons (SPPs) on opposite sides of the metal film, the "WA-SPP" effect. Rigorous coupled-wave analysis (RCWA) calculations on a 2D model, which are shown to give WA-SPP features very similar to that of 3D Finite-Difference Time- Domain (FDTD) calculations, are performed to determine how system parameters influence the strength of the WA-SPP effect. Herein we show that the optimum values for the film thickness and hole diameter are 45 and 175 nm, respectively.

Fluorescence is a highly sensitive, precise, and convenient detection technique that is widely used in chemistry, molecular biology and clinical laboratories. Fluorescence in the near-IR (700 - 900 nm) offers higher molar absorptivity and significantly lower background signals from scatter than those generated by visible wavelength excitation. The advantageous characteristics of near-IR fluorescence, primarily the reduced background signals, make this region of the spectrum ideal for enhancement by metal nanostructures. Though multiple groups have successfully demonstrated metal enhanced fluorescence, there remain several challenges in transferring this technology from the research stage to the commercial stage. Using a LI-COR Odyssey® Infrared Imaging System, we quantitatively analyzed the effects of silver particle geometries, including size, shape, and density of metal nanostructures, on the fluorescence enhancement of Near-IR fluorophores. Using silver island film coated glass slides, we were able to obtain an 18-fold enhancement of IRDye®700 and a 15-fold enhancement of IRDye®800 labeled DNA oligos over dye on plain glass. We further analyzed the silver-coated glass surfaces for enhancement reproducibility and linearity. We demonstrated that the metal enhanced emissions remained reproducible across a slide surface, and remained linear over several orders of magnitude. Finally, using a highly quenched labeled protein, we were able to show an enhancement and release of the quenched fluorescence, generating a 40-fold enhancement in the fluorescence emissions when spotted on a silver nanostructure coated glass slide. Generating silver nanostructure coated slides that enhance fluorescence while maintaining linearity and reproducibility will provide a class of new tools benefiting molecular biologists.

The effects of thin silver films embedded in a tandem pentacene/C₆₀ photovoltaic cell are investigated. A 2 nm Ag film improves the device's power efficiency under white light illumination from 0.32% to 1.11% by almost doubling its open circuit voltage and enhancing its short circuit current density. The doubled open circuit voltage is due to the formation of two separated photovoltaic pentacene/C₆₀ cells in series where discontinuous silver clusters provide carrier recombination centers. The increased photocurrent density is partly ascribed to improved charge separation and transport associated with the silver layer. In addition, wavelength dependent measurements suggest that plasmon-enhanced light absorption by pentacene due to surface plasmon resonance of silver nanoparticles contributes as much as a factor of 4 to the power efficiency near the plasmon resonance around 450 nm.

Vibrational Sum Frequency Generation (VSFG) on gold and silver nanoparticles capped with alkanethiols is studied. Aggregation of nanoparticles is characterized using TEM and SEM methods. VSFG process is enhanced due to the coupling of surface plasmon induced by the visible radiation in gold nanoparticle with vibrational transition of chemisorbed alkanethiol excited by the infrared beam. VSFG spectra show methyl and methylene stretch transitions. The ratio of their intensities varies with changing size of the particles and length of alkane chain. Dramatic change in intensity ratio and overall enhancement of VSFG intensity is observed when aggregation of gold nanoparticles occurs. For the first time we report the mode-specific SFG enhancement, namely, the methyl antisymmetric stretch gains the highest intensity. One possible explanation is that enhancement is caused by the change in SFG selection rules due to the effect of locally inhomogeneous electric field of plasmon. VSFG response from aggregates is significantly depolarized in comparison with response from non-interacting particles. This can be due to the depolarization of plasmon induced in aggregates of metallic nanoparticles. Divergence of VSFG beam from aggregates is stronger than that of the beam from non-interacting particles. This can be attributed to the incoherent nonlinear scattering in aggregates due to depolarization of surface plasmon. Potential applications of SFG nanoprobes for imaging, IR radiation conversion, and opto-electronic integrated circuits are discussed.

It is well known that propagation ranges of surface plasmon-polaritons supported by thin metal films are significantly limited by losses due to the concentration of a portion of the mode's energy within the metal. Propagation distances may be increased by using lower frequency light or thinner metal films. Implementation of these techniques is limited, however, and may not always be desirable. A layered structure, which allows for propagation ranges to be increased while holding the wavelength of the light and film thickness constant has been proposed. The surface plasmon-polariton guide consists of a metal film surrounded above and below by a thin, low index of refraction dielectric layer. When set in a dielectric cladding of higher index of refraction, the thickness of the inner dielectric layer may be increased up to a cutoff to achieve dramatic extension in propagation range. The effects of adjustment to parameters of the guide, such as the dielectric cladding index of refraction, metal film thickness and wavelength are discussed. Due to the fact that propagation distance and mode confinement are closely related, these two properties are investigated together, and the merits of the guide are discussed.

We demonstrate the use of gold nanorods as molecularly targeted contrast agents for two-photon luminescence (TPL) imaging of cancerous cells 150 μm deep inside a tissue phantom. We synthesized gold nanorods of 50 nm x 15 nm size with a longitudinal surface plasmon resonance of 760 nm. Gold nanorods were conjugated to antibodies against epidermal growth factor receptor (EGFR) and labeled to A431 human epithelial skin cancer cells in a collagen matrix tissue phantom. Using a 1.4 NA oil immersion objective lens, we found that excitation power needed for similar emission intensity in TPL imaging of labeled cells was up to 64 times less than that needed for two-photon autofluorescence (TPAF) imaging of unlabeled cells, which would correspond to a more than 4,000 times increase in emission intensity under equal excitation energy. However, the aberrations due to refractive index mismatch of the immersion oil and the sample limit imaging depth to 75 μm. Using a 0.95 NA water immersion objective lens, we observe robust two-photon emission signal from gold nanorods in the tissue phantoms from at depths of up to 150 μm. Furthermore, the increase in excitation energy required to maintain a constant emission signal intensity as imaging depth was increased was the same in both labeled and unlabeled phantom, suggesting that at the concentrations used, the addition of gold nanorods did not appreciably increase the bulk scattering coefficient of the sample. The remarkable TPL brightness of gold nanorods in comparison to TPAF signal makes them an attractive contrast agent for early detection of cutaneous melanoma.

Nanoscale variations in the local fields and material properties can enable higher-multipole (magnetic-dipole and electric-quadrupole) contributions to the nonlinear response in addition to electric-dipole contributions. Moreover, the local-field distribution in the structure is important to achieve favorable interaction with the locally varying nonlinearity. Local-field enhancement is particularly important for nonlinear optical effects. Extremely small features of a few nm, such as nanogaps between two particles, are expected to be particularly beneficial for field localization and enhancement. Here, we provide evidence of multipole interference in polarized secondharmonic generation from arrays of L-shaped gold nanoparticles. We also prepare T-shaped gold nanodimers and vary the size of the nanogap between their vertical and horizontal bars. Surprisingly, the second-harmonic signals do not decrease trivially with increasing gap size, because the gap region is nearly centrosymmetric, thereby forbidding second-order effects. Instead, asymmetric local fundamental field distributions along the dimer perimeter are favorable, in accordance with the symmetry rule.

We demonstrate both experimentally and computationally that SHG from arrays of T-shaped gold nanodimers with differing nanogap sizes results from asymmetry in the local field distribution rather than strict dependence on the nanogap size. Normal-incidence SHG measurements reveal that the SHG responses depend non-trivially on the nanogap size. Calculations show that strong orthogonal polarization components, which are not present in the exciting field, are induced, and that these induced components yield the dominant SHG response. The calculations also reveal that field enhancement is roughly independent of nanogap size and persists even for large nanogap sizes. A simple phenomenological model wherein the local surface susceptibility of the nanodimer interacts with the local field distribution along the nanodimer perimeter qualitatively explains the experimental results with good agreement.

It has recently been shown¹ that tapered arrays of thin metallic wires can guide and manipulate electromagnetic fields on the sub-wavelength spatial scale. Our computations demonstrate that two types of nanoscale imaging applications using terahertz and mid-infrared waves are enabled: image magnification, where the tapered wire array acts as a multi-pixel endoscope by capturing an electromagnetic field profile created by deeply subwavelength objects at the endoscope's tip and magnifying it for observation, and radiation focusing, where the image of a large mask at the endoscope's base is projected onto a much smaller image at the tip. The most important result of this work is the demonstration of a new computational technique that enables extracting TE, TM and TEM modes from a full 3-D electromagnetic simulation. Through extraction of the TEM electric field from the total electric field we show that the physical mechanism of the image propagation along the guiding structure is indeed the TEM modes of the multiconductor array.

F&diaero;rster resonant energy transfer (FRET) between the CdTe quantum dot (QD) acting as donors and acceptors is investigated at nanoscale proximity to gold nanoparticles (Au NPs). Photoluminescence (PL) studies of the acceptor QD emission from a mixed monolayer showed a distance dependent enhancement of the acceptor emission compared with that achieved for a donor-acceptor mixed monolayer in the absence of the Au NP layer. Time-resolved photoluminescence measurements showing a reduction in the donor lifetime, accompanied by an increase in the acceptor PL lifetime, provide further evidence for surface plasmon enhanced FRET.

We have studied the effects of planar inversion symmetry and particle-coupling of gold nanoparticle (NP) arrays by angle dependent second-harmonic generation (SHG). Time- and angle- resolved measurements were made using a mode-locked Ti:sapphire 800 nm laser onto gold NP arrays with plasmon resonance tuned to match the laser wavelength in order to produce maximum SHG signal. Finite-difference time domain simulations are used to model the near-field distributions for the various geometries and compared to experiment. The arrays were fabricated by focused ion-beam lithography and metal vapor deposition followed by standard lift-off protocols, producing NPs approximately 20nm high with various in-plane dimensions and interparticle gaps. Above a threshold fluence of ~ 7.3 × 10^-5 mJ/cm² we find that the SHG scales with the third power of intensity, rather than the second, and atomic-force microscopy shows that the NPs have undergone a reshaping process leading to more nearly spherical shapes.

Dielectric thin films on a metal surface are an efficient means in terms of effective index contrast to realize optical elements for surface plasmon (SPs). We show that laterally structured thin films can on one hand be applied as SP lenses or prisms. On the other hand, they can be applied as SP waveguides, including bends and couplers.

We report on the direct measurement of dispersion relations of plasmons confined in atomically thin metal films and wires by electron energy loss spectroscopy in wide energy-momentum range. Ultrathin Ag films are prepared on single crystal Si surfaces by molecular beam epitaxy, and its crystallinity is checked by electron diffraction. For the case of multi-atomic-layer Ag films, two plasmon modes are observed at around 3.9 eV and 1.8 eV which are localized at the top and the bottom surfaces of the films, respectively. For the case of Ag monoatomic layer, a single mode is observed that steeply disperses in the mid-infrared range. Nonlocal and quantum effects are found to be essential in understanding its full plasmon dispersion curve up to the critical wave number of Landau damping. For the case of Au atom chains, an anisotropic sound-wave-like plasmon dispersion is found that clearly shows 1D plasmon confinement in each atom chain.

A plasmonic coupling device consisting of an array of ellipsoidal silver nanoparticles embedded in silica in close proximity to a silver surface is studied. By tuning the inter-particle spacing, the shape of the particles in the array, and the height of the array above the silver film, the array-mediated surface plasmon excitation is studied. Finite Integration Technique simulations of such a plasmon coupler optimized for operation at a free space wavelength of 676 nm are presented. Plane wave normal incidence excitation of the system results is seen to result in resonantly enhanced fields near the nanoparticles, which in turn excite surface plasmons on the metal film. The existence of an optimum particle-surface separation for maximum surface plasmon excitation efficiency is demonstrated. Analysis of the frequency dependent electric field in the simulation volume as a function of particle aspect ratio reveals the influence of the particle resonance and the surface plasmon resonance on the excitation efficiency.

A unifying model based on enhanced elctron-hole recombination rate generated by surface plasmon (SP) waves of Au nanoparticles (NPs), electrons transferred from the CdSe quantum dots (QDs) to the Au NPs, as well as the photoexcitation wavelength is proposed to explain the observed optical enhancement and quenching from Au and CdSe nanocomposites. In our system, the photoluminescence-enhancement ratio can be manipulated to ~130, the largest value ever reported. Our experimental results clarify the ambiguity in controlling the light emission enhancement of semiconductor nanocrystals which are coupled with the SP waves of metal NPs.

We study nonlinear optical response of nanofabricated gold particles with sub-100-nm spatial resolution by means of non-linear near-field scanning optical microscopy (NSOM). In our instrument, femtosecond pulses at 800 nm wavelength are coupled to hollow-pyramid aperture sensors. Such probes show high throughput and preserve pulse duration and polarization, enabling the achievement of sufficiently high peak power in the near field to perform nonlinear optics on the nanoscale. We study second-harmonic generation (SHG) from gold nanoparticles of two different kinds, namely, closely-packed gold triangles and nanoellipsoids. We find a strong dependence of SHG efficiency on the shape and the fine structure of the nanoparticles. Near-field SHG is therefore a subwavelength resolution probe of local field enhancements occurring at specific sites of the particles. This work is focused on the dependence of NSOM linear and nonlinear images on the aperture size and linear polarization direction of light. Our measurements give strong evidence that SHG is mainly excited by a high field concentration at the rims of the metal NSOM aperture. This conclusion is supported by the high spatial resolution obtained for SHG even with apertures so large that FW imaging shows much poorer resolution.

Electromagnetic eigenstates are used to try and develop a systematic approach for computing the macroscopic electric and magnetic response of a two-constituent composite medium where neither constituent exhibits any intrinsic magnetic response, i.e., the magnetic permeability equals 1 everywhere. Results for two-dimensional arrays of equally long circular cylinders appear promising as far as computational power is concerned. Proximity of the physical parameters of the system to a resonance of the composite microstructure increases the chances of getting negative values for both the electric permittivity and the magnetic permeability.

We develop a method to study the optical and magneto-optical response of perforated metallic films with magneto-optic media embedded within their holes. Due to the strong electromagnetic field confinement associated with the excitation of the transmission resonances appearing in this type of structures and nonreciprocal nature of the magneto-optical phenomena, strongly enhanced conversion of the polarization state in both reflected (magneto-optical Kerr effect) and transmitted (magneto-optical Faraday effect) waves was found. Possibility to reach huge rotation angles is demonstrated by increasing magneto-optic holes filler/background optical contrast, which appears to be responsible for the resonance quality.

In this paper we present a novel means of active control of a plasmonic system at the quantum level: the electron spin. Through manipulation of far infrared wavelength optical energy in the near-field, we experimentally show that electron spin can influence near-field mediated light propagation through a spintronic medium consisting of a dense ensemble of bimetallic ferromagnetic (F)/nonmagnetic(N) microparticles. The metallic medium under study is composed of ferromagnetic particles with nonmagnetic nano-layers, and it resembles a rudimentary spinplasmonic device that can be both optically and magnetically activated. Far infrared light transmission through the spinplasmonic medium shows very strong magnetic field dependent attenuation and optical phase retardation of the transmitted far infrared light pulses. The large attenuation is due to the interface resistance resulting from dynamic electron spin accumulation in N as spin-polarized electrons are optically driven from the F layer to the N layer. The demonstration of spin-dependent light propagation offers the basis for the development of novel devices and opens the door to a new field of spinplasmonics.

The extent to which light can be focused with conventional optics is limited to λ/2 by the phenomenon of diffraction. Optical energy needs to be focused to less than 100nm to enable improvement and innovation in nanoscale applications. A novel lens structure to focus surface plasmons to a few tens of nanometer with high throughput is described here. This paper outlines the theoretical design and fabrication considerations of this novel plasmonic lens structure.

Enhancement of Brillouin light scattering (BLS) at the wavelength of 532 nm was observed from Rayleigh-like and Sezawa-like acoustic modes of alkaline-earth boro-aluminosilicate glass covered with periodic arrays of gold nanodisks. This enhancement is attributed to mediation of surface plasmons of the nanodisks. For nanodisks with diameters of 71 nm to 90 nm, heights of 30 nm, and periodicity of 100 nm, the maximum measured surface-plasmon enhancement of BLS intensity was, respectively, ~ 2.4 and ~ 5.6 for Rayleigh-like and Sezawa-like modes, relative to the intensity from a gold film with the same fractional coverage area but without surface-plasmon coupling. The maximum for the Rayleigh-like modes occurs with the smallest-diameter nanodisks, and that for the Sezawa-like modes occurs with the largest-diameter nanodisks. The angular dependence is relatively broad. Calculations employing the discrete dipole approximation were used to predict the electric-field intensities in the gold disks and nearby glass as a function of nanodisk diameter. The average calculated intensity at the top surface of the gold increases with decreasing diameter, consistent with the experimental results for Rayleigh-like modes and the expectation that surface ripple is the dominant scattering mechanism for such modes. The results of this study suggest that nanodisk arrays can provide a platform for practical implementation of surface-enhanced BLS analogous to other surface-enhanced spectroscopies, and suggest the additional possibility of substantially extending the range of wave numbers in BLS through plasmonic-crystal band folding.

Three kinds of periodic gold nanostructures: nanoslit array, nanohole array and nanogrid, were fabricated and compared. These nanostructures were made on a 130nm-thick gold film with the same 600nm-period. Each array size was 150μm x 150μm in square. The transmission spectra show 630nm peak in air and about 830nm peak in water environment. These peaks are verified by the resonances of surface plasmonic waves on the outside surface. The wavelength sensitivities of the surface plasmon resonance in aqueous condition are tested. They are 590.9nm, 556nm and 514nm per refractive index change for the nanoslit, nanogrid and nanohole structures, respectively. The higher sensitivity of nanoslit array is attributed to the extraordinary transmission of transverse magnetic wave in the nanoslit gap.

The Bloch modes of a periodic slit array in a metallic slab are identified, then used to investigate the transmission of light through sub-wavelength slits residing in a finite-thickness slab. Specifically, the Bloch mode method is used here to study Fabry-Perot-like resonances within individual slits, in conjunction with the onset of surface plasmon polariton (SPP) resonances and in the vicinity of the Wood anomalies. Although the results largely agree with our earlier numerical simulations obtained with the Finite-Difference-Time-Domain (FDTD) method, there are indications that the FDTD method has difficulty with convergence at and around resonances; the points of agreement and disagreement between the two methods are discussed in the present paper. When the period p of the slit array is comparable to (or somewhat below) the incident wavelength λ_o, the Bloch mode method requires only the 10-20 lowest-order modes of the slit array to achieve stable solutions; we find the Bloch mode method to be an effective tool for studying dielectric-filled apertures in highly conductive hosts.

Silver nanoparticles were obtained by UV radiation of silica films containing Ag⁺ ions. 2d-hexagonal nanostructured sol-gel thin films were prepared by dip-coating method using the non-ionic diblock copolymer Brij58 to produce channels into the film, which house the silver nanoparticles. An absorption band located at 438 nm was detected; it corresponds to the surface plasmon resonance. High resolution transmission electronic microscopy measurements show core-shell structures of silver-silver oxide nanoparticles in these sol-gel silica films. These optical properties were modeled and well fitted with the Gans theory considering refractive index higher than the one coming from host matrix. This index is explained because the silver oxide shell modifies the local surrounding medium of the metallic nanoparticles and therefore plays an important role in the optical properties of the films.

This paper reports the details regarding the design and fabrication of gold nanostructures on glass substrates through nanosphere lithography (NSL) for the application of localized surface plasmon resonance (LSPR), which can be used for biosensors. It is realized through gold film deposition on nanospheres dispersed on a surface and subsequent anisotropic etching. Depending on the gold deposition and etching conditions, a variety of gold nanostructure shapes can be obtained. So far through this method, only 2D nanocrescents are reported. In this paper it is pointed out that both 2D and 3D non-conformal nanostructures can be fabricated, and some 2D and 3D profiles of the obtainable nanostructures are simulated by our programs under various deposition and etching conditions. The fabrication processes of the nanostructures on glass substrates are also reported, and the simulated profiles of such nanostructures coincide well with the experimental results. These results prove that our profile simulation program can realize the design of 2D and 3D nanostructures obtainable by nanosphere lithography, and reduce the effort and cost for achieving optimized nanostructures by experiments in the trial and error stage.

Sol-gel silica films containing silver ions were annealed in a rich-hydrogen atmosphere and subsequently in a rich-oxygen atmosphere. High resolution transmission electronic microscopy measurements shown unusual core-shell structures of silver-silver oxide nanoparticles in these films. The optical properties of these nanostructures exhibited red shift and damping in the UV-vis spectra. In order to calculate the optical properties were used the Mie theory using two approaches. The first one, corresponding to the core-shell model that includes a refractive index of the shell (n_s) different to the one of the host matrix (n_m). While in the second approach, we replaced in the Mie theory the refractive index of the environment (silica) by a local refractive index (n_l) depending on the thickness of the silver oxide shell. Both calculations given the same results because they are equivalents.

Surface Enhanced Raman Spectroscopy is a powerful analytical technique capable of single molecule detection sensitivity. We have detected SERS on the tip of a 3 mm-core diameter PMMA plastic optical fiber. The technique involves deposition of 30 nm gold nanoparticles followed by deposition of sample of interest to be analyzed. SERS enhancement has been demonstrated for several chemicals like glycerin and dye Rhodamine 6G as well biological molecules like Acetaminophen, aspirin and Streptavidin and poly-L-Lysine. It is shown that interfering spectrum of PMMA can be subtracted to reveal the SERS spectrum of molecule of interest. The technique can simplify SERS detection by connecting the other end of fiber directly to a spectrometer. SERS was recorded for various concentrations of analytes. Using a focused 633 nm laser, a detection sensitivity of 0.1picogram was established.

The approach described in the present paper was applied for analysis of Fe-based amorphous and crystallized alloys. All the analyzed specimens have Sw~1. Using classical approach to the Kramers-Kronig transform this value is insufficient for refraction index and therefore optical conductivity determination. The present paper considers new ways of Kramers-Kronig transform accuracy increase by use of high-order quadrature method and new approach to reflectivity extrapolation. Using the advanced described approach a set of amorphous and crystallized alloys of Fe₈₀TM₅B₁₅ type was analyzed where TM is the 3d-transition metal. It is shown while adding a small amount of Ti, V or Cr the observed plasma frequency tends to be about 3 to 4 eV higher than in case Mn, Co or Ni impurity was added. The proposed method error of the optical constants determination estimate is not greater than 15% for refraction and absorption indexes and 25% for conductivity even in case experimental spectral range is relatively small. Plasma frequency of analyzed specimens was calculated. The methods of plasma frequency determination were compared. Determination of base points by direct method allows significant accuracy increase and adequate error estimation of this value.

For realization of highly integrated optical circuits, various metallic nanostructures supporting the propagation of surface plasmon polaritons have been extensively studied experimentally and theoretically in recent years. This paper reports on the development of a numerically stable and accurate finite-difference-based bidirectional beam propagation method (FD-BiBPM) for analyzing piecewise z-invariant plasmonic structures. Our method is developed based on the scattering operators. The adoption of complex coefficient rational approximations to the square root operator allows to correctly model the propagation of evanescent modes excited at discontinuity interfaces. In view of the large index contrast at metal-dielectric interfaces, a fourth-order accurate finite difference formulation for discretization is incorporated to the present method and its fine treatment of these interfaces guarantees accuracy. By using the present method, the reflection and transmission spectra of the Bragg gratings consisting of a thin metal film embedded in dielectric medium and an array of equidistant metal ridges on each side of the film are calculated. The good agreement of our results with the previously reported simulations illustrates the potential of the newly developed FD-BiBPM for the analysis of longrange surface plasmon polariton (LRSPP) waves guided along the described Bragg gratings.

We present FDTD simulations of light interaction with two dimensional silver structure made of the tip forming array of channel plasmon-polariton waveguides, that confines light to a small width beam or focus. The flat end of triangle formed plasmon-polariton waveguides array is illuminated with the optical range H-polarized Gaussian beam or plane wave. Light is transported through the structure with plasmon-polariton waves on surface of metal. At sloped planes energy from plasmon-polariton modes is refracted at an angle defined by propagation constants of modes. Propagation constants of excited plasmon-polaritons modes in waveguides array are predicted by semi-analytical calculations. Choosing canal widths, their separation and slop angle, we can couple energy from waveguides array to both free space propagation beams and to surface waves of the whole tip structure, which have propagation constants greater than free space waves. Combined effects of refraction, diffraction on the narrow end of the structure and the plasmon-polaritons like properties of surface waves on the whole structure lead to significant local enhancement of the field, high directivity of the output energy and focusing with resolution below diffraction limit for free space.