Dynamics at the air-water interface revealed by evanescent wave light scattering

A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle illumination. Peak width and height are affected by the interfacial profile and the focusing of the beam. In addition, the propagation of capillary waves was studied at the surface of pure water and in the presence of latex particles and amphiphilic diblock copolymers. The range of the scattering vectors where propagating surface waves were detected is by far wider than standard surface quasi-elastic light scattering (SQELS) and comparable with those of X-ray photon correlation spectroscopy (XPCS).     

Enhanced backward scattering by surface plasmons on silver film

Surface plasmon and its potential application in nanotechnology have attracted a remarkable amount of attention recently due to their novel properties. In this work we present an angularly resolved surface plasmon scattering study on a primitive metal surface. Using a reversed attenuated total reflection (RATR) setup in the experiment, we obtained a double-crescent shaped and enhanced scattering pattern at far field. The scattering pattern as a function on the variation of angle and polarization of incident beam are studied. Both theoretical and experimental results reveal an enhanced backward scattering by surface plasmon excitation. Consequently, it is shown that this angularly resolved surface plasmon scattering measurement can be employed for resolving a richness of nanoscale surface textures. PACS 42.79.-e; 42.30.Wb; 78.20.Ci     

Relating temperature dependence of atom scattering spectra to surface corrugation

It is suggested that a measurement of the temperature dependence of the most probable intensity of energy-resolved atom-surface scattering spectra can reveal the strength of the surface corrugation. To support this conjecture, a classical mechanical theory of atom scattering from a corrugated surface, valid in the weak corrugation limit, is developed. The general result for the scattering probability is expressed in terms of spatial integrals over the impact parameter within a surface unit cell. For the case of a one-dimensional corrugation, approximate expressions for the scattering probability are obtained in terms of analytic closed form expressions. As an indicator of its relation to experimental measurements, calculations using a one-dimensional corrugation model are compared with data for Ar scattering from a molten Ga surface and an approximate value of the corrugation height parameter is extracted.     

Scattering of surface plasmon-polaritons and volume waves by thin gold films

The specific features of elastic scattering of volume waves and surface plasmon polaritons by polycrystalline gold films have been investigated. An analysis of the relative scattered energy, power spectral density of surface roughness, and integral and angular dependences of scattering of waves of different nature indicates a strong nonradiative multiple scattering of surface plasmon polaritons in gold films. When roughness increases, this scattering leads to an increase in scattering isotropy and to a partial loss of structural information about gold films. The analysis of the scattered energy of surface plasmon polaritons with application of the data on multifractal dimension of gold surface indicates also that the radiative scattering of surface plasmon polaritons depends on both the rms surface roughness and the surface wave propagation length.     

实际加工表面红外激光散射特性的实验研究

为了研究激光在实际加工表面的散射特性,利用分辨率为10 nW的激光功率计PM100D,波长为1550 nm的激光器和精密转台,自行设计并搭建了半球空间中目标表面散射特性的测量系统. 以典型的刨床加工的若干标准粗糙度比较样块为被测目标,在1550 nm红外激光以不同方位照射下,测量了微观具有V形槽结构的不同粗糙度的样块表面的散射功率分布. 实验结果转换成双向反射分布函数后,对比分析了入射光方位、入射角和表面粗糙度对此类典型表面散射特性的影响,并分析了特殊散射场形成的原因. 结果表明,表面纹理、入射角以及粗糙度均对目标表面的散射特性有规律性影响,这一结果对于具有规律性加工纹理表面的散射特性的研究和建模有一定的参考价值,对激光技术在实际加工表面的应用研究提供了一定的基础. 关键词： 散射特性 双向反射分布函数 红外激光 实际加工表面     

Multiple scattering and neutralization aspects of low energy noble gas ions incident on a Cu (110) crystal

Experiments have been done with 1 keV Ne⁺ ions bombarding a Cu (110) single crystal in a (111) plane. From the measured energy spectra of the scattered ions the minimum and maximum scattering angles for multiple scattering on the surface are determined. These minimum and maximum scattering angles were also calculated using a computer model. The parameters for an interatomic potential function between ion and metal atom are determined by comparison of the experimental and calculated scattering angles. A neutralization model for an energetic ion at an atomic surface is given. The reliability of this model is tested by comparison of the results of computer calculations and the measured peak intensity distributions as a function of the scattering angle.     

Compton scattering of 59.5 keV gamma rays from p-Si sample in an external electric field

This study is related to Compton scattering of photons from a p-Si sample whose surface charge density distributions are changed by an external electric field. The external electric field intensity in the range 0-75 kV/m was used to change the surface charge density distributions of the sample. The sample surface perpendicular to the electric field was selected as the scattering surface. The p-Si sample was bombarded by 59.5 keV γ-photons emitting from an Am-241 point source. The Compton scattered photons at an angle of 90^o were detected by an Si(Li) detector. The Compton scattering intensity suddenly increased with the application of the electric field since the applied electric field distorts both the negatively charged scattering center (free electron, bound electron, ionized acceptor) and the positively charged scattering center (hole) and their momentum distribution in the sample. There is a good third-order polynominal relation between the Compton scattering intensity and the increasing (or decreasing) electric field intensity. The results show that the positively charged scattering centers behave like negatively charged scattering centers, but the latter are slightly more effective than the former in the Compton scattering of γ-rays from the sample in the electric field.     

On argon beams as tools to probe surfaces

We present experimental data and a theoretical analysis for the scattering of an argon beam from the (001) surface of LiF. The scattering pattern of the Ar beam was investigated for incident energies between 0.089 and 0.350 eV and for a variety of polar and azimuthal incidence angles. We find a bilobular scattering pattern for small incidence angles and along the direction of maximum corrugation on the surface, and a broad peak centered around the specular direction for higher incidence angles. An interaction potential based on the effective medium theory has been evaluated. The corrugation of this potential across the surface is in fair agreement with the data interpreted using the classical rainbow angles. Such corrugation is smaller than the one determined by He scattering, in agreement with previous Ar/metal surface investigations.     

Structure analysis of the KBr(100) surface An investigation with a new method for surface analysis of insulators

The surface structure of highly insulating KBr(100) was investigated by a new technique, impact collision atom scattering spectroscopy with detection of neutrals (NICASS). By using neutral atoms in the scattering experiment as projectiles [different from conventional ion scattering (ISS)], uncertainties in the experimental data due to surface charging effects are avoided. As a result, a surface structure model for KBr(100) is presented. By comparing the experimental scattering information with computer simulated data, an inward relaxation in the first layer has been deduced. The relaxation is different for the two components K and Br: K is shifted by 0.5 Å and Br by 0.3 Å, resulting in a surface rumpling of 0.2 Å.     

Hf-radiowave specific second-order sea-surface-scattering cross-section matrix

The modified small-perturbation method is employed to derive analytic formulas for the hf-radiowave specific sea-surface second-order scattering cross section (SSC) matrix for an arbitrary scattering geometry. The elimination of SSC-matrix singularity at the limit of an ideally conducting statistically rough surface is examined. A numerical study of the scattering properties of the sea surface is performed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 5, pp. 381–397, May, 1992.     

Quantitative evaluation of equatorial small-angle X-ray scattering for cylindrical fibers

Elongated microvoids, internal fibrillar structure, and edge scattering from both surface refraction cause an equatorial streak in small angle X-ray scattering. A model for analyzing the edge scattering of fibers is proposed. Simulation results indicate that the intensity of edge scattering from surface refraction of a cylindrical fiber is strong and makes an important contribution to the equatorial streak. Two factors influence edge scattering intensity. One is the sample-to-detector distance (D); edge scattering intensity increases with increasing D. The equatorial streak becomes weak when D is shortened. The other factor is the refraction index. Edge scattering intensity increases as the real component of the refraction index decreases. In experiment, weak or even no equatorial streaks were found for samples measured in a roughly index-matching fluid. Edge scattering can be eliminated or weakened, and it can be calculated by comparing the intensities of a cylindrical fiber when it is measured in air and in index-matching fluid. The simulation data are basically in agreement with the experimental data.     

Surface plasmon damping due to rough boundary scattering

The surface plasmon damping due to carriers scattering at the statistically rough (semiconductor-dialectric) interface is considered. The specular parameter and the integral relation are used as the boundary condition for a non-equilibrium part of the distribution function. There exist certain cases when the rough surface scattering of carriers is shown to play an important role in the surface plasmon damping.     

Light scattering from bulk and surface spin waves in opaque ferromagnets; The influence of quadratic coupling terms

We calculate the light scattering spectrum from spin waves, for backscattering from an opaque ferromagnet with magnetization parallel to the surface. The spectra contain features arising from both bulk and surface magnons. Including the quadratic terms in the spin density in the fluctuating part of the dielectric tensor leads to an asymmetry in the Stokes/anti-Stokes ratio for scattering for both bulk and surface waves. Our calculations give a good account of the data reported by Grunberg and Metawe, for scattering from EuO.     

Effects of Breaking Waves on Composite Backscattering from Ship-Ocean Scene

The existence of the sea surface is bound to affect the electromagnetic(EM) scattering from marine targets. When dealing with the composite scattering from targets over a sea surface by applying high-frequency EM theories,the total scattering field can be decomposed into three parts in low sea states, namely, the direct scattering from the sea surface, the direct scattering from targets and the coupling scattering between the sea surface and targets. With regard to high sea states, breaking waves make the direct scattering from the sea surface and the coupling scattering more complicated. To solve this issue, a scattering model is proposed to analyze the composite scattering from a ship over a rough sea surface under high sea states. To consider the effect of breaking waves,a three dimensional geometric model is adopted together with Ufimtsev's theory of edge waves for the scattering from a breaker. In addition, the coupling scattering between targets and breaking waves is taken into account by considering all possible scattering paths. The simulated results indicate that the influence of breaking waves on the scattering field from the sea surface and on the coupling field is non-negligible, and the numerical results also show the effectiveness of the proposed scattering model.     

Analysis of one-dimensional rough surface scattering based on bidirectional reflectance distribution function model

Through in-depth analysis of the scattering properties of a one-dimensional random rough surface, a method to calculate the spatial bidirectional reflectance distribution function (BRDF) characteristics of a randomly rough surface is proposed. The scattering characteristics of an electrically large rough surface can be substituted by combination of subsection electromagnetic fields. The radar cross-section (RCS), which is transformed from the BRDF, is compared with numerical results from the Method of Moment (MoM). The agreement of the results verifies that this method could calculate the electromagnetic scattering field efficiently and straightforwardly. Moreover, the resulting combined fields from the BRDF of subsections in the rough surface show a good match with the entire scattering field of a whole surface, which indicates that a large electrically rough surface could be feasibly and effectively substituted with the combination of scattering elements using the BRDF method and the statistical method.     

Study on the shadowing effect for optical wave scattering from randomly rough surface

Based on the Kirchhoff approximation for rough surface scattering and by calculating the shadowing function of the rough surface, the formula of the scattering cross section of the dielectric rough surface is presented with consideration of the shadowing effect for the optical wave incidence. It is obtained that in comparison with the conventional Kirchhoff solution, the shadowing effect should not be neglected for the optical wave scattering from the rough surface. The influence of the shadowing effect for different incidence angle, surface root mean square slope, and surface roughness on the scattering cross section is discussed in detail.     

Numerical simulation methods for rough surface scattering

Numerical methods are of great importance in the study of electromagnetic scattering from random rough surfaces. This review provides an overview of rough surface scattering and application areas of current interest, and surveys research in numerical simulation methods for both one- and two-dimensional surfaces. Approaches considered include numerical methods based on analytical scattering approximations, differential equation methods and surface integral equation methods. Emphasis is placed on recent advances such as rapidly converging iterative solvers for rough surface problems and fast methods for increasing the computational efficiency of integral equation solvers.     

Scattering of Solar and Atmospheric Background Radiation from a Target

Light scattering property of environment is very important in theoretical study and application of the remote sensing. What's more, it is valuable for infrared radiation, imaging, and the detection of target and tracking. In this paper, solar and atmospheric background radiation, and their scattering property from target are discussed. BRDF (Biodirectional Reflectance Distribution Function) is a very important quantity that shows the radiation and reflection feature of target. According to electromagnetic radiant and scattering theories, the relationship between laser radar scattering cross section (LRCS) and BRDF is introduced. LOWTRAN model is an effective method of calculating the spectral distribution of solar and atmospheric radiation. Here it is applied to compute solar and atmospheric background radiation scattered from a target. The relative equations are deduced. Thus, the spatial and spectral distribution of scattering light is given. As a special example, for the Lambert's surface, the equations are simplified. As a result, the spatial and spectral distributions scattering radiation of solar and atmospheric background from a rough painted surface are present. The scattering of solar radiation plays a primary role in MIR region, but scattering of atmospheric background radiation is higher in LIR region. At the same time, there is obviously specular reflectance for solar radiation due to coherent scattering from rough surface.     

A statistical model for the scattering of atoms from randomly stepped surfaces

The scattering of an atomic beam from a randomly stepped surface has been calculated using the hard corrugated wall model. Under the basic assumption that scattering from the step edges may be neglected the scattering equation can be solved without any further approximation. The solution displays the usual diffraction peaks each of them is broaden by a term characterizing the step configuration. If the step distribution is ergodic and stationnary in space this term is the characteristic function of the difference of level between two point of the surface considered as a random variable. Statistical models for the step repartition at the surface are proposed and the scattering intensity is derived in a closed form. The main result is that the broadening of the peaks varies from no broadening to a maximum according as the interferences from waves reemitted by the various terraces are constructive or destructive. A comparison is made with previous experimental data from which an estimation of the average step separation can be drawn. The sensitivity of the atomic beam scattering to steps is found to be more than one step every one hundred crystal atoms.