Scattering of an electromagnetic wave from a slightly random dielectric surface: Yoneda peak and Brewster angle in incoherent scattering

Abstract

The scattering of an electromagnetic wave from a two-dimensional, slightly rough dielectric surface is studied based on the stochastic functional approach. It is shown that in the case of TM(p)-polarized incidence there exists a zero in the incoherent scattering at the angle we call the ‘Brewster scattering angle’, which depends on the incident angle in contrast to the Brewster angle of coherent reflection which is independent of the incident angle, that a ‘quasi-anomalous scattering’ can generally occur in the optically denser medium at the critical angle of total reflection in both TE(s)- and TM(p)-polarized incidence, regardless of which side of the random surface is illuminated, and that the Yoneda peak in the x-ray scattering can be interpreted as a special case of the quasi-anomalous scattering which becomes sharper when the relative refractive index becomes closer to unity as in the x-ray region. Cross-polarized scattering and enhanced backscattering due to the second-order effect are also calculated.     

Control of absorption spectrum of a one-dimensional resonant photonic crystal

The crystal under consideration is a layered structure consisting of alternating layers of two materials, one of which is a resonantly absorbing gas. It is shown that the combination of the dispersion of an atomic gas with the dispersion of a photonic-bandgap structures allows one to efficiently control the transmission spectra of s- and p-polarized modes in these combined systems. It is found that the spectrum is highly sensitive to the position of the gas resonance frequency with respect to the bandgap edge and to a change in the gas pressure. The transmission, reflection, and absorption spectra of the resonant photonic crystal are studied at an angle of incidence equal to the Brewster angle of a seed photonic crystal. Possible applications of the found particular features of the dispersion of resonant photonic crystals are discussed.     

Traveling of light through a 1D photonic crystal containing a defect layer with resonant dispersion

Spectral properties of a 1D photonic crystal that is comprised of two multilayered dielectric mirrors and a nanocomposite layer between them as a structural defect are studied. The nanocomposite consists of silver nanoballs dispersed in a transparent matrix and is characterized by an effective resonant permittivity. The spectral manifestation of the defect mode splitting for the s-polarized waves is studied as a function of the angle of incidence and concentration of nanoballs. Specific features of the transmission spectra for the s- and p-polarized waves are established for the angle of incidence equal to the Brewster angle of the seeding photonic crystal. It is shown, in particular, that, in the region of the continuous transmission spectrum of the spolarized waves, there arises an additional bandgap caused by mixing of the resonant mode with photonic modes.     

Shaping of nanostructured surface in femtosecond laser ablation of thin films

We report that the nanostructured surface of diamondlike carbon films can be shaped so as to have a sawlike pattern with obliquely incident p-polarized femtosecond laser pulses. The nanoscale surface shape was observed as functions of incident angle, superimposed number and fluence of laser pulses and characterized with height and slope angle of the inclined surface. It is shown that the inclined shape is formed with the non-uniform spatial distribution of the local field enhanced on the nanostructured surface.     

Magnetorefractive effect in nanocomposites: Dependence on the angle of incidence and on light polarization

The polarization and angular dependences of the magnetorefractive effect (MRE) in metal-insulator nanocomposites in reflection and transmission geometries have been calculated in terms of the high-frequency, spin-dependent tunneling mechanism. The MRE exhibits a weak polarization and angular response at small angles of incidence. The MRE in reflection and transmission starts to grow strongly with increasing angle of incidence. The MRE in reflection in nanocomposites with metal contents corresponding to the insulating phase near the percolation threshold reaches the largest values with p-polarized light at an angle of incidence close to the Brewster angle. The results of the calculation are in a qualitative agreement with experimental data.     

Numerical simulation of the optical reflection and transmission coefficients of a periodic surface of metallic nanowire grating

The optical reflection and transmission coefficients of a metallic nanograting have been studied with the use of numerical simulation in a wide range of the size of structural units of the grating. The grating is composed of silver nanowires arranged periodically on a quartz substrate. The cases of s- and p-polarized incident waves have been considered. In particular, it has been found that the spectral dependence of the reflection and transmission coefficients of the nanograting becomes oscillatory and exhibits several deep minima when all structural parameters of the grating (the nanowire’s width and height, and the grating period) approach tens of nanometers. The physical reason of the appearance of these oscillations has been analyzed. It has been shown how the depth and position of the discovered minima depend on the light angle of the incident wave and the rotation angle of the grating around its normal surface.     

Simulations of Two-Dimensional Photon Scanning Tunneling Microscope by Boundary Integral Equation Method: p-polarization

Accurate simulations of a two-dimensional photon scanning tunneling microscope (2D-PSTM) for incident p-polarized waves (TM-mode) have been performed by the boundary integral equations called guided-mode extracted integral equations. The method used in this paper is a global method and the case of uncoated dielectric probe is treated. Complete and rigorous integral equations for a given configuration of 2D-PSTM have been solved numerically by the conventional boundary-element method with high accuracy. Using three universal laws, i.e., the optical theorem, the energy conservation law and the reciprocity relation for incident p-polarized waves, numerical results have been confirmed. The basic physical characteristics of interaction between probe-tip and near-field for incident p-polarized waves are compared in detail with those of incident s-polarized waves (TE-mode) which are previously reported.This paper was originally presented at the 5th International Conference on NEAR FIELD OPTICS and RELATED TECHNOLOGIES(NFO-5), which was held on December 6–10, 1998 at Coganoi Bay Hotel, Shirahama, Japan, in cooperation with the Japan Society of Applied Physics and Mombusho Grant-in Aid for Scientific Research on Priority Areas “Nearfield Nano-optics” Project, sponsored by Japan Society for the Promotion of Science.     

Research of negative refractive direction of P-light in metal

This paper studies the light propagation in metal. Using the complex wave vector, we analyze the propagation direction of light energy in a metal, and find that P and S-polarized light propagate at a different refraction angle when a beam of light passes from the air to a metallic boundary at a certain angle. Especially, P-polarized light will be refracted at a negative angle, and the direction of P-polarized light is the same side of the incident light.     

Surface-plasmon-polariton waves guided by the uniformly moving planar interface of a metal film and dielectric slab

We explored the effects of relative motion on the excitation of surface-plasmon-polariton (SPP) waves guided by the planar interface of a metal film and a dielectric slab, both materials being isotropic and homogeneous. Electromagnetic phasors in moving and non-moving reference frames were related directly using the corresponding Lorentz transformations. Our numerical studies revealed that, in the case of a uniformly moving dielectric slab, the angle of incidence for SPP-wave excitation is highly sensitive to (i) the ratio β of the speed of motion to speed of light in free space and (ii) the direction of motion. When the direction of motion is parallel to the plane of incidence, the SPP wave is excited by p-polarized (but not s-polarized) incident plane waves for low and moderate values of β, while at higher values of β the total reflection regime breaks down. When the direction of motion is perpendicular to the plane of incidence, the SPP wave is excited by p-polarized incident plane waves for low values of β, but s-polarized incident plane waves at moderate values of β, while at higher values of β the SPP wave is not excited. In the case of a uniformly moving metal film, the sensitivity to β and the direction of motion is less obvious.     

Lossy effects on the lateral shifts in negative-phase-velocity medium

Theoretical investigations of the lateral shifts of the reflected and transmitted beams were performed, using the stationary-phase approach, for the planar interface of a conventional medium and a lossy negative-phase-velocity medium. The lateral shifts exhibit different behaviors beyond and below a certain angle, for both incident p-polarized and incident s-polarized plane waves. Loss in the negative-phase-velocity medium affects lateral shifts greatly, and may cause changes from negative to positive values for p-polarized incidence.     

a-Si:H/a-SiNx:H超晶格薄膜光致发光性质的研究

本文报道了a-Si:H/a-SiNx:H超晶格薄膜光致发光某些性质的研究。实验发现,这种超晶格薄膜光致发光的强度和峰值能量随交替层a-Si:H厚度,测量温度及光照时间等而变化。同时还发现,在阴、阳两极上,利用GD法沉积的样品,发光强度和峰值能量也有所不同。文中对这些实验结果作了初步解释。     

Determination of electron-diffusion length from photocurrent characteristics of the structure ITO/a-SiC:H(p-type)/a-Si:H/a-Si:H(n-type)/Pd

In this study the electron diffusion length L _n is determined from the relative spectral response of the photocurrent characteristics of the p/i/n sandwich structure ITO/a-SiC:H(p-type)/a-Si:H/a-Si:H(n-type)/Pd. The techniques used for the preparation of the a-Sic:H and a-Si:H amorphous films were glow-discharge and rf magnetron sputtering, respectively. The thickness of the p-type, intrinsic and n-type layer were 400 Å, 7000 Å and 600 Å, respectively. The response of the short-circuit current density J _sc was measured versus the photon energy hv at both constant light intensity and constant temperature. The electron diffusion length was found to be 0.31 m by means of the method of Agarwala and Tewary. Although, in the case of single crystals many diffusion length measurements have been made, there are only few papers for amorphous silicon this films [1]. As it is well-known, the diffusion length of the charge carriers is the most important parameter from the point of view of solar cell applications [2]. In order to obtain a high efficiency in a solar cell all carriers created under illumination in the intrinsic layer should reach the electrodes [3]. In the case that the thickness of the intrinsic layer is much larger than the diffusion length, not all carriers can reach the electrodes and, accordingly, a low efficiency results [4]. On the other hand, carriers which reach the electrodes without thermalizing do not contribute to the photocurrent and finally the efficiency of the solar cell is negatively affected. In order to avoid such an effect to a large extent, the thickness of the amorphous layers in a p/i/n solar cell must be conveniently chosen compared to the diffusion length of the carriers.Here it is aimed to determine the electron diffusion length. In order to achieve this goal, the photocurrent characteristics of an ITO/a-SiC:H(p-type)/a-Si:H/a-Si:H(n-type)/Pd structure was measured versus the photon energy at constant light intensity and constant temperature. In order to determine the electron diffusion length, the method of Agarwala and Tewary [5] was utilized.     

Applying the phase difference property of polarization angle for measuring the concentration of solutions

This paper proposes a simple method for measuring the concentration of solutions based on the phase difference of internal reflection polarization angle and circularly polarized heterodyne interferometry. For a circularly polarized heterodyne light beam incident on the boundary surface between a hemispherical prism and a test solution, the reflected light passes through a properly oriented analyzer for interference. The phase difference between s- and p-polarized light is sensitive to the solution concentration when the incident angle equals the internal reflection polarization angle. Based on these effects, the resulting phase difference makes it possible to analyze the concentration of solution through heterodyne interferometry. The experiments in this study confirm the feasibility of this method, which provides the advantages of simple installation, ease of operation, and high accuracy.     

Physical nature of anomalous optical transmission of thin absorptive corrugated films

The enhancement of p-polarized light transmittance through periodically relief thin absorptive film on dielectric or semiconductor substrate was considered theoretically. The calculation of transmittance/reflectance was performed in the framework of modified differential formalism method. Numerical results obtained for noble metals (Au, Ag and Cu) under arbitrary relief correlation between two sides of film allow ascertaining physical nature of surface electromagnetic fields responsible for the enhancement transmittance effect. These are Fano, Zenneck-Sommerfeld and Brewster modes on the interfaces with absorbing medium. For anticorrelated reliefs of opposite film surfaces the bound of their modes was found especially effective. The article is published in the original.     

Three dimensional a-Si:H thin-film solar cells with silver nano-rod back electrodes

We present three dimensional (3-D) amorphous silicon (a-Si:H) thin-film solar cells with silver nano-rods as back electrodes, which are fabricated by low cost nano imprint lithography (NIL). After conformal deposition of thin metal and semiconductor layers, we can achieve a dome-shaped geometry, which is shown to be effective in reducing the reflectance at the front surface due to the graded refractive index effect. In addition, the enhancement of the diffused reflectance over a broad wavelength in this dome-shaped geometry provides light trapping due to the increase in the effective light propagation length. Using this 3-D solar cell, we achieved 54% increase in short circuit current density and 45% increase in the conversion efficiency compared to the control cells with flat Ag surfaces. This 3-D structure can be also used for improving light harvesting in various photovoltaic devices regardless of materials and structures.     

Brewster angle for anisotropic materials from the extinction theorem

We explore the physical origin of the Brewster angle in the external and internal reflections associated with an anisotropic material. We obtain the expressions of the reflected fields and the existence condition of the Brewster angle by using the extinction theorem. It is found that the Brewster angle will occur if the total contribution of the material’s electric and magnetic dipoles to the reflected field becomes zero. In internal reflection, the requirements on the material parameters ε and μ for the Brewster angle are the same as those in external reflection, and the Brewster angle is just the refraction angle in external reflection at the incidence of the external Brewster angle. The results of the present paper are applicable to dielectric and magnetic materials, including metamaterials. PACS 73.20.Mf; 78.20.Ci; 41.20.Jb; 42.25.Fx     

Light diffraction on acoustophotorefractive holographic gratings

The intermediate regime of light diffraction on acoustophotorefractive holographic gratings written in cubic photorefractive crystals according to the synchronous-detection mechanism is studied. It is shown that the diffraction efficiency in sillenite-type gyrotropic crystals only slightly depends on the incident light polarization and the external electric field. The highest diffraction efficiency in nongyrotropic crystals was achieved for p-polarized writing and reading light and at a considerable external electric field strength.     

Size effects in the internal reflection in gold cluster films in polarization modulation experiments

The internal reflection in gold nanocluster films in the Kretschmann geometry is studied using polarization modulation of electromagnetic radiation. The reflection coefficients R _s and R _p for s- and p-polarized light, respectively, as well as their difference ΔR = R _s − R _p , are measured as functions of the angle of incidence of electromagnetic radiation at different wavelengths in the range of 0.6–1.6 μm. A topological size effect is found in the interaction of light with the cluster electronic system, which consists of the fact that the surface plasmon resonance in gold cluster films can be excited by both p- and s-polarized light. It is found that the magnitude and the sign of curvature of the angular dependence of ΔR are related to the degree of resonance with light of either only p-polarization or both polarizations simultaneously.     

Investigation of Brewster anomalies in one-dimensional disordered media having Lévy-type distribution

In this paper, we calculate the localization length of a TM electromagnetic wave in unitof system length versus incident angle in a disordered layered structure where therefractive index of one of its constituents follows a Lévy-type distribution with a powerexponent α.The incident angle at which the localization length takes the maximum value is called thegeneralized Brewster angle as before. However, in contrast to previous works with a weakdisorder, the wave incident at generalized Brewster angle is not always in the extendedregime. For special values of α and the frequency, the system is in a localizedstate at this angle. But, the localization length at this Brewster angle is always largerthan that at other angles. The effects of α variation on the localization length at thisBrewster angle and its position are investigated for different frequencies. Thelocalization at this angle degrades with increasing α for all frequencies. Atsome working frequencies, the generalized Brewster angle is a decreasing function ofα. However,at other frequencies, the dependence of generalized Brewster angle on α is not monotonic. Forincident angles smaller than a specific angle, the localization length increases withincreasing α.However, for incident angles larger than this specific angle, there are incident angles atwhich any increase of α leads to the decrease of localization length. Inother words, for these incident angles, the improvement of Anderson localizationsurprisingly happens with decrease of disorder strength and the refractive index contrast.     

Goos–H?nchen shift at an interface of a composite material: effects of particulate clustering

The Goos–H?nchen (GH) shift of a p-polarized light beam reflected from an interface of a composite material of particulate metals in a dielectric host is studied theoretically using effective medium approaches, with focus on the effects due to the clustering of the metal particles. With application of a fractal-clustering model, it is shown that the composite can have optically metallic behavior even for relatively low volume fraction of metal when clustering takes place, with appreciable negative GH shifts to take place for light of long wavelengths close to grazing incident angles. Furthermore, we confirm that large reflectance is always accompanied with this metal behavior, thus rendering these shifts easily observable.