Scattering from rough surfaces

Scattering from rough surfaces is studied using a perturbative treatment of the Ewald-Oseen extinction theorem. Expressions for the first and second order fields in the roughness parameter are presented for arbitrary incident fields and used for the calculation of scattering and extinction cross sections. The cross sections are shown to have contributions from diffuse scattering as well as from surface polariton emission and include the hitherto studied effects such as Smith-Purcell radiation, Wood anomalies and reflectance drops at rough surfaces.     

Determination of the equivalent solid angles of radiation reflected from rough surfaces of opaque materials

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 3, pp. 456–462, March, 1989.     

White light scattering from non-Gaussian rough surfaces

Optics and Spectroscopy - A method is proposed for calculating the spectral correlation function of light intensity scattered from non-Gaussian rough surfaces. The correlation function of a...     

Scattering of He atoms from rough surfaces

Three diverse rough surfaces have been studied using inelastic He scattering. The first is an ion bombarded Ag(110) surface where a broadened specular peak remains visible but scattering remains entirely elastic as viewed by the incoherent component. The second is a cleaved Te(10 ) surface composed of helical chains where the roughness originates from thermal oscillations and scattering is almost entirely inelastic. Thirdly, a glass (7740) disc is shown to be physically rough but the surface is sufficiently rigid to yield largely elastic incoherent scattering.     

弹性波在固体自由粗糙平界面上的散射

利用散射幅度矩阵的概念来处理弹性波在粗糙界面弹性介质中的散射问题。利用微扰近似解边界方程,对散射幅度进行求解,得到了散射幅度的0阶、1阶和2阶解。同时分析了粗糙起伏高度符合高斯分布时,散射幅度的数学期望值和方差,它们分别代表平均场和声场在偏离镜面方向的起伏。最后进行了实验。     

Pulse broadening of enhanced backscattering from rough surfaces

Recently, we presented a study of pulse scattering by rough surfaces based on the first-order Kirchhoff approximation which is applicable to rough surfaces with RMS slope less than 0.5 and correlation distance l≳λ. However, there has been an increased interest in enhanced backscattering from rough surfaces, study of which requires inclusion of the second-order Kirchhoff approximation with shadowing corrections. This paper presents a theory for the two-frequency mutual coherence function in this region and shows that the multiple scattering on the surface gives rise to an additional pulse tail in the direction of enhanced backscattering. The theory predicts pulse broadening approximately 20% greater than that caused by single scattering alone for a delta-function incident pulse and typical surface parameters. Analytical results are compared with Monte Carlo simulations and millimetre-wave experiments for the one-dimensional rough surface with RMS height 1λ and correlation distance 1λ, showing good agreement.     

Rigorous solutions for electromagnetic scattering from rough surfaces

Abstract

First, the rough surface scattering problem is formulated from a statistical point of view. Then, different numerical schemes that permit one to solve Maxwell equations without approximation are presented for the three-dimensional scattering problem. Particular attention is paid to boundary integral methods and to the numerical techniques developed to handle large linear systems when short-range interactions dominate. Lastly, several important connected issues that require further numerical and theoretical improvements are discussed.     

Pulse broadening of enhanced backscattering from rough surfaces

Abstract

Recently, we presented a study of pulse scattering by rough surfaces based on the first-order Kirchhoff approximation which is applicable to rough surfaces with RMS slope less than 0.5 and correlation distance l?λ. However, there has been an increased interest in enhanced backscattering from rough surfaces, study of which requires inclusion of the second-order Kirchhoff approximation with shadowing corrections. This paper presents a theory for the two-frequency mutual coherence function in this region and shows that the multiple scattering on the surface gives rise to an additional pulse tail in the direction of enhanced backscattering. The theory predicts pulse broadening approximately 20% greater than that caused by single scattering alone for a delta-function incident pulse and typical surface parameters. Analytical results are compared with Monte Carlo simulations and millimetre-wave experiments for the one-dimensional rough surface with RMS height 1λ and correlation distance 1λ, showing good agreement.     

Transition radiation from polarization charges

Summary A treatment of transition radiation is presented. This is based on the fields produced by the polarization charges in the radiation zone. These charges are extracted from the exact forms of the fields which were derived previously. A distinction is found between the radiation in the forward and in the backward regions. This would call for experimental verification. Comparison with other treatments shows similarity in the general features but important differences in the details.

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Riassunto Si presenta una trattazione della radiazione transitoria. Essa è basata sui campi emessi nella regione asintotica dalle cariche di polarizzazione. Queste cariche sono estratte dalle forme esatte di campi che erano stati precedentemente derivati. Si verifica una distinzione chiara fra la radiazione nella direzione avanti e indietro. Questo neccesiterebbe una verifica sperimentale. Il confronto con altri trattamenti mostra una somiglianza nelle linee generali ma anche importanti differenze nei dettagli.

     

Growth of rough surfaces

The growth of objects with rough surfaces is a common phenomenon. We describe several models used in the study of the temporal evolution of fluctuating interfaces and then we explain the dynamical scaling in this class of growth models with self-affine surfaces. The recent progress in this field is reviewed. Much emphasis is put on roughness properties and in particular on a possible kinetic roughening transition — a nonequilibrium analog of the thermal roughening transition. Both analytical and numerical results for scaling exponents are summarized and indications of a phase transition in some models are discussed.     

Nanoadhesion between rough surfaces

A model is developed to describe the adhesion between deformable fractal surfaces over the mesoscopic realm that covers the familiar range of interest in nanotechnology from atomic dimensions to microns. This model helps us gain a quantitative understanding of the variation of adhesion with surface energy, with microstructure of rough surfaces, and with bulk deformability. The present analysis goes beyond the Gaussian distribution of asperity heights by investigating the influence of the microstructure of self-affine fractal surfaces. Our calculation reveals that orders of magnitude increase in adhesion are possible as the roughness exponent decreases.     

The reflection of ultrasound from partially contacting rough surfaces

Ultrasound is commonly used to detect and size cracks in a range of engineering components. Modeling techniques are well established for smooth and open cracks. However, real cracks are often rough (relative to the ultrasonic wavelength) and closed due to compressive stress. This paper describes an investigation into the combined effects of crack face roughness and closure on ultrasonic detectability. A contact model has been used to estimate the size and shape of scatterers (voids) at the interface of these rough surfaces when loaded. The response of such interfaces to excitation with a longitudinal ultrasonic pulse over a wide range of frequencies has been investigated. The interaction of ultrasound with this scattering interface is predicted using a finite-element model and good agreement with experiments on rough surfaces is shown. Results are shown for arrays of equi-sized scatterers and a distribution of scatterer sizes. It is shown that the response at high frequencies is dependent on the size, shape, and distribution of the scatterers. It is also shown that the finite-element results depart from the mass-spring model predictions when the product of wave number and scatterer half-width is greater than 0.4.     

Multiple light scattering from metal and dielectric rough surfaces

Abstract

A numerical study is done on light scattering from one-dimensional random rough surfaces supporting both dielectrics and metals. The influence of the corrugation on the Brewster angle as well as on the angular distribution of transmitted intensity into the dielectric is investigated. The authors also obtain enhanced backscattering in the light reflected from metallic surfaces. Finally they discuss the influence of roughness on the drop of reflectance due to polariton absorption.     

Fluctuations of the acoustic field Bragg-backscattered from rough surfaces

A rigorous theory of backscattering from slightly rough, statistically non-stationary surfaces is developed. The development proceeds through the application of two ensemble averages: the first is applied to all realizations of the surface having fixed non-stationary features, and the second over all non-stationary surface characteristics. The resulting theory is applied to acoustic sea-floor reverberation, where it is found that non-stationarity must be assumed to obtain agreement with observed reverberation fluctuations. The analysis is further extended to the time domain where it is demonstrated that, for Bragg scatter, no reduction in the predicted fluctuations occurs for frequency diverse waveforms, thus providing a method of differentiating Bragg scatter from other non-resonant scattering processes.     

Exact multiple scattering of waves from random rough surfaces

The exact multiple scattering theory of waves scattered from a random rough surface is presented. We give an iterative series for the mean scattered intensity (I (Q)) for all order in the statistics. We show that the coherent intensity for large correlation distances approaches the value obtained in the Kirchhoff approximation by Beckmann. Also we prove that a “white noise” surface reflects specularly the whole incident intensity.     

The depolarization of light scattered from rough metal surfaces

To describe the depolarization of the electromagnetic field scattered from rough metal surfaces, a finite, non-vanishing value of the conductivity has to be considered. To reveal the modifications imposed by a complex dielectric constant, the Beckmann formula is expanded in power series of slope terms. We then arrive at an analytic expression which is convenient for evaluation as a function of the parameters involved. With this expression, plots of the cross-polarization ratio vs. angle of incidence and vs. slope are presented.