共查询到20条相似文献,搜索用时 46 毫秒
1.
We show that a weakly absorbing, strongly scattering (white) medium can be made very strongly absorbing at any frequency within its strong-scattering bandwidth by optimizing the input electromagnetic field. For uniform absorption, results from random matrix theory imply that the reflectivity of the medium can be suppressed by a factor ~(?(a)/?)N(-2), where N is the number of incident channels and ?, ?(a) are the elastic and absorption mean free paths, respectively. It is thus possible to increase absorption from a few percent to >99%. For a localized weak absorber buried in a nonabsorbing scattering medium, we find a large but bounded enhancement. 相似文献
2.
Expressions are obtained for the efficiency of absorption and scattering of radiation by uniform spheroids in the quasi-static approximation and the region of their applicability is studied. The prolate and oblate nonabsorbing particles with refractive indices 1.1≤n≤10 and axial ratios 1.1≤a/b≤100 were studied. The approximation expressions are found for the particle size at which the efficiency factors are calculated in the quasi-static approximation with an accuracy of 1%. 相似文献
3.
V. A. Loiko A. V. Konkolovich A. A. Miskevich 《Journal of Experimental and Theoretical Physics》2016,122(1):176-192
Light scattering by an optically anisotropic liquid crystal (LC) droplet of a nematic in an isotropic polymer matrix is considered in the Wentzel–Kramers–Brillouin (WKB) approximation. General relations are obtained for elements of the amplitude matrix of light scattering by a droplet of arbitrary shape and for the structure of the director field. Analytic expressions for the amplitude matrices are derived for spherical LC droplets with a uniformly oriented structure of local optical axes for strictly forward and strictly backward scattering. The efficiency factors of extinction and backward scattering for a spherical nonabsorbing LC droplet depending on the LC optical anisotropy, refractive index of the polymer, illumination conditions, and orientation of the optical axis of the droplet are analyzed. Verification of the obtained solutions has been performed. 相似文献
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V. P. Dick 《Optics and Spectroscopy》2007,103(4):632-639
The maximum value of the light extinction coefficient μ, which can be observed in a dispersive medium with a relative refractive index n of the scattering particles, is studied within the framework of a quasi-crystalline approximation for nonabsorbing dispersive media consisting of monodisperse spherical scatterers. A change in the diffraction parameter x of the scattering particles and their volume concentration c v is accompanied by nonmonotonic variations of the extinction coefficient, and the function μ(x, c v ) exhibits several maxima. The dimensions and concentrations of particles are determined, for which the extinction coefficient reaches the absolute maximum μmax. The μmax value exhibits a monotonic growth with increasing relative refractive index n of the scattering particles. The conditions of validity of the Ioffe-Regel criterion of radiation localization have been studied. It is established that the localization in nonabsorbing dispersive media can be observed only for n ? 2.7. The intervals of x and c v in which the criterion of radiation localization is satisfied in dispersive media consisting of particles with n = 3.0 and 3.5 are determined. 相似文献
7.
The small-slope approximation (SSA) in rough-surface scattering theory uses the surface slope as a small parameter of expansion. But, from the physical point of view, the slope may not be a restrictive parameter because we can change the slope of a surface simply by tilting the coordinate system. We present the theory of rough-surface scattering in a coordinate-invariant form. The new method, tilt-invariant approximation (TIA), leads to a different expansion that does not require that the slope of a surface be small. For a small Rayleigh parameter this approximate solution provides the correct perturbation theory, for a large Rayleigh parameter it provides the Kirchhoff approximation with several correcting terms. 相似文献
8.
《Waves in Random and Complex Media》2013,23(4):361-380
Abstract The small-slope approximation (SSA) in rough-surface scattering theory uses the surface slope as a small parameter of expansion. But, from the physical point of view, the slope may not be a restrictive parameter because we can change the slope of a surface simply by tilting the coordinate system. We present the theory of rough-surface scattering in a coordinate-invariant form. The new method, tilt-invariant approximation (TIA), leads to a different expansion that does not require that the slope of a surface be small. For a small Rayleigh parameter this approximate solution provides the correct perturbation theory, for a large Rayleigh parameter it provides the Kirchhoff approximation with several correcting terms. 相似文献
9.
V. A. Loiko U. Maschke V. Ya. Zyryanov A. V. Konkolovich A. A. Miskevich 《Optics and Spectroscopy》2011,111(6):866-872
We consider monolayer polymer films with oriented droplets of a nematic liquid crystal (LC). Relations for the coherent transmission
coefficients of a layer of oriented ellipsoidal droplets and for the intensity of light scattered by monolayers of spherical
and spheroidal droplets have been obtained. The amplitude-phase screen model and the interference approximation of the theory
of multiple wave scattering have been used. To describe light scattering by an individual ellipsoidal droplet with inhomogeneous
surface binding, we have developed an anomalous diffraction approximation. For monolayers of spherical LC droplets, the coherent
scattering coefficients and the angular scattering structure have been analyzed. The internal structure of nematic droplets
have been calculated by the relaxation method based on the solution of the minimization problem of the free energy volume
density. We have studied basic regular features of light scattering by a monolayer with homogeneous and inhomogeneous boundary
conditions at the LC-polymer interface. We show that, for films that contain droplets with inhomogeneous boundary conditions
of the tangentially normal type, the angular structure of the scattered light is asymmetric with respect to the polar scattering
angle. 相似文献
10.
The theory of distortion correction by phase conjugation, developed since the discovery of this phenomenon many years ago, applies to situations when the field that is conjugated is monochromatic and the medium with which it interacts is deterministic. In this Letter a generalization of the theory is presented that applies to phase conjugation of partially coherent waves interacting with either deterministic or random weakly scattering nonabsorbing media. 相似文献
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We propose to use channels in strongly scattering nonabsorbing random media for guiding electromagnetic waves, and demonstrate this concept using near-field microscopy of surface plasmon polaritons (SPP's) propagating along the gold film surface covered with randomly located scatterers. In the wavelength range of 725-765 nm, we observe complete inhibition of the SPP propagation inside the random structures composed of approximately 50-nm-wide gold bumps and their clusters with the density of 50 microm(-2), as well as well-defined SPP guiding along corrugation-free 2- and 4-microm-wide channels. 相似文献
13.
The two-beam approximation of dynamic electron diffraction in crystals is deduced from successive scattering by two-dimensional gratings. The scattering-amplitude caused by the single grating (phase-grating) is determined by the atomic scattering factors of the single atoms. The use of real atomic scattering factors leads here to the same solutions as the twobeam theory, using the Schroedinger-equation. Anomalous absorptions effects are described in the usual theory by introducing a complex lattice potential into the Schroedinger-equation, taking into account inelastic scattering. A more exact calculation of only elastic scattering by a single atom results in complex atomic scattering factors. Using the complex atomic scattering factors one can describe the anomalous absorption, if recursion-formulae for successive scattering are applied. On the other hand, the transformation to differential equations leads to results, which are not in agreement with experiments. The influence of inelastic scattering for the anomalous absorption can be neglected compared with the complex atomic scattering factors. 相似文献
14.
The geometrical optics approximation is shown for the first time to be sufficient for determining the lens transparency in the Z-scan method for nonabsorbing media. The diffraction effects are taken into account in calculating the cross section of a focused Gaussian beam. With the use of the matrix method, the lens transparency of a Z-scan scheme is determined as a quantity inverse to the square of its normalized optical power. At a small phase incursion, the expressions for the lens transparency obtained by different methods coincide. 相似文献
15.
V. A. Loiko U. Maschke V. Ya. Zyryanov A. V. Konkolovich A. A. Miskevich 《Optics and Spectroscopy》2011,110(1):110-118
We considered light scattering by a polydisperse ensemble of droplets of a nematic liquid crystal. To model light scattering
by a monolayer of polymer-dispersed spherical droplets of a nematic liquid crystal with cylindrical symmetry of its internal
structure, we proposed a semianalytical modeling method. The method is based on interference approximation of the theory of
multiple wave scattering, anomalous diffraction approximation, and effective-medium approximation. The method takes into account
cooperative optical effects in concentrated, partially ordered layers and can be used to analyze the small-angle structure
of the intensity of scattered radiation in relation to the concentration, size, polydispersity of liquid crystal droplets,
orientation of their optical axes, and refractive indices of the liquid crystal and polymer. The obtained relations can be
applied to solving direct and inverse problems of light scattering in composite liquid crystal materials using data of polarization
measurements. We present graphical results of solving the direct problem for components of the polarization vector of scattered
wave. These results illustrate the formation of an angular structure for monolayers with a high concentration of polydisperse
droplets of the liquid crystal in the range of small scattering angles (0 < θ
s
≤ 8°). 相似文献
16.
Coherent x-ray radiation of a relativistic electron crossing a single-crystal plate in the Laue scattering geometry is considered
in a two-wave approximation of the dynamic diffraction theory [1]. Analytical expressions describing the spectral-angular
distribution of parametric x-ray radiation (PXR) and diffraction transition radiation (DTR) formed on the atomic planes located
at an angle δ to the crystal plate surface (asymmetric scattering) are derived. Dependence of the spectral-angular density
of PXR, DTR, and their interference term on the angle δ is investigated.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 80–89, August, 2008. 相似文献
17.
Sandra Jacquier Frédéric Gruy 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(17-18):2794-2803
We previously [Jacquier S, Gruy F. Approximation of the light scattering cross-section for aggregated spherical non-absorbent particles. JQSRT 2008;109:789–810] reformulated the anomalous diffraction (AD) approximation to calculate the light scattering cross section of aggregates by introducing their chord length distribution (CLD). It was applied to several ordered aggregates. This new method is entitled ADr, with the r for rapid because this one is at least 100 times faster than the standard AD method. In this article, we are searching for an approximated expression for CLD suitable all at once for ordered and disordered aggregates. The corresponding scattering cross-section values are compared to the ones coming from the standard AD approximation. 相似文献
18.
L. E. Paramonov 《Optics and Spectroscopy》2012,112(5):787-795
Light scattering by isotropic ensembles of ellipsoidal particles is considered in the Rayleigh-Gans-Debye approximation. It is proved that randomly oriented ellipsoidal particles are optically equivalent to polydisperse randomly oriented spheroidal particles and polydisperse spherical particles. Density functions of the shape and size distributions for equivalent ensembles of spheroidal and spherical particles are presented. In the anomalous diffraction approximation, equivalent ensembles of particles are shown to also have equal extinction, scattering, and absorption coefficients. Consequences of optical equivalence are considered. The results are illustrated by numerical calculations of the angular dependence of the scattering phase function using the T-matrix method and the Mie theory. 相似文献
19.
Small-slope approximation (SSA) is a scattering theory that is supposed to unify both the small-perturbation model and the Kirchhoff approximation (KA). We study and compute the second-order small-slope approximation (SSA2) in a high-frequency approximation (SSA2-hf) that makes it proportional to the first-order term, with a roughness-independent factor. For the 3D electromagnetic problem we show analytically that SSA2-hf actually meets KA in the case of perfectly conducting surfaces. This no longer holds in the dielectric case but we give numerical evidence that the two methods remain extremely close to each other for moderate scattering angles. We discuss the potential applications of SSA2-hf and give some 2D numerical comparison with rigorous computations. 相似文献
20.
F. Ehlotzky 《Physics letters. A》1974,47(6):491-492
By means of a simple approximation we evaluate the Kapitza-Dirac diffraction probabilities for scattering of electrons in backward direction by a standing wave of intense coherent light. 相似文献