镜面物体往复通过弱湍流大气系统的成像

分别利用部分相干理论、以广义随球波函数为基础的Ｋａｒｈｕｎｅｎ－Ｌｏｅ′ｖｅ展开和相干成像理论研究了弱湍流像差大气照明系统互强度函数传输特征和位地湍流介质中镜面物体成像规律。结果表明：仅当反射光束相干尺度（成像光束等效直径）小于成像孔径的尺度时才能改善湍流大气中两次成像的质量。     

Weak gravity-like force detector by “Atom interferometers”

We study nonlinear interaction of counter-propagating plane light waves in a semi-infinite isotropic lossless nonlinear Kerr medium and report existence of several regions of optical-polarization-multistability. The counter-propagating waves may be produced by normal reflection of an incident beam by a mirror in the nonlinear Kerr medium. We obtain nonlinear coupled differential equations for Stokes parameters of the two beams and solve them following the method of Prakash et al. [Mod. Phys. Lett. B 14, 47 (2000)] and the boundary conditions at the mirror. We find that, for the same incident intensity and for the same polarization state of the incident beam, output beam may exist in several stable polarization states.     

Total reflection of light propagating from an isotropic medium to an anisotropic medium

We study the propagation of light from an isotropic medium to an anisotropic medium. It is shown that total reflection can occur only for propagation from a denser medium to a rarer medium; this result does not agree with that of Lin and Wu [Opt. Lett. 23, 22 (1998)].     

非常偏振光在单轴晶体表面的反射-透射研究

为分析非常偏振光在晶体表面的能量损耗,给出一种求解反射率和透射率的方法,即根据电磁场的边值关系以及晶体的双折射和双反射现象,求解晶体光轴在入射面内时,非常偏振光从各向同性介质入射到晶体和从晶体出射到各向同性介质两种情况的反射率和透射率的方法,并给出反射率和透射率的解析解,同时得到对于晶体光轴在入射面内的情况,光轴的取向对非常偏振光反射率的大小几乎没有影响,但对产生全反射的临界角θc影响较大的结论。实验上用LiNbO3晶体验证了非常偏振光从各向同性介质入射到晶体时的反射率公式。求解方法简单实用,所给的表达式具有一般性,可以直接使用。     

光波p分量在单轴晶体表面反射和折射的相位特性

根据单轴晶体的双折射和双反射性质,通过数值计算研究了光轴在入射面内并与晶体界面成任意角时光波p分量在单轴晶体表面反射和折射的相位特性.结果表明,光轴取向对相位变化有较大影响,光从光疏各向同性介质射入单轴晶体时,光轴方向改变反射光p分量的相位突变点,但对折射光p分量相位无影响.光从光密各向同性介质射入单轴晶体未发生全反射时,光轴方向同时影响p分量反射光和折射光的相位突变|发生全反射后,光轴方向影响反射光p分量的相位变化曲线.从单轴晶体出射到光疏各向同性介质未发生全反射时,光轴方向改变反射光p分量的相位跃变规律,折射光p分量在光轴方向和晶面成小角度时在布儒斯特角附近发生相位突变|发生全反射后,反射光p分量的相位变化曲线随光轴方向的改变发生较大变化.     

One-Dimensional Inverse Scattering Problem in Acoustics

We are concerned with the inverse scattering problem (ISP) in acoustics within the Marchenko inversion scheme. The quantum ISP is first discussed and applied in order to exhibit certain characteristics and application prospects of the method which could be useful in extending it to classical systems. We then consider the ISP in acoustics by assuming plane waves propagating in an elastic, isotropic, and linear medium. The wave equation is first transformed into a Schrödinger-like equation which can be brought into the Marchenko integral equation for the associated nonlocal kernel the solution of which provides us the full information of the underlying reflective profile. We apply the method in several model problems where the reflection coefficient of the multi-layer reflective medium is used as input to the ISP and in all cases we obtain excellent reproduction of the original structure of the scatterer. We then applied the inverse scattering scheme to construct profiles with certain predetermined reflection and transmission characteristics.     

Effect of phonon damping on the resonance reflection of a transverse sound wave from a planar defect in a crystal

Resonance scattering of a transverse sound wave by a planar defect in an elastic isotropic medium is studied in a wide range of values of the ratio of the damping length and the size of the region of localization of longitudinal oscillations. The transition between two limiting cases is described. The character of the transition is demonstrated by typical plots of the dependence of the reflection and transmission coefficients on the parameter relating the wavelength of the incident wave and the strength of the defect. It is shown that renormalization of total reflection into conventional dissipative passage occurs for values of this parameter below a certain critical value.     

Boundary states at reflective moving boundaries

We derive and evaluate boundary states for Maxwell’s equations, the linear, and the nonlinear Euler gas-dynamics equations to compute wave reflection from moving boundaries. In this study we use a Discontinuous Galerkin Spectral Element method (DGSEM) with Arbitrary Lagrangian–Eulerian (ALE) mapping for the spatial approximation, but the boundary states can be used with other methods, like finite volume schemes. We present four studies using Maxwell’s equations, one for the linear Euler equations, and one more for the nonlinear Euler equations. These are: reflection of light from a plane mirror moving at constant velocity, reflection of light from a moving cylinder, reflection of light from a vibrating mirror, reflection of sound from a plane wall and dipole sound generation by an oscillating cylinder in an inviscid flow. The studies show that the boundary states preserve spectral convergence in the solution and in derived quantities like divergence and vorticity.     

Reflection and transmission phenomena of waves propagating between an isotropic medium and an arbitrarily oriented anisotropic medium

We theoretically analyze waves propagating between an isotropic medium and an anisotropic medium. Closely examining the boundary condition reveals that the phenomenon of nonsymmetrical reflection occurs when the wave propagates from an anisotropic to an isotropic medium. Calculating the reflection of thin films requires correcting the phase change in each reflected trip in the Airy formula. Analytical results of measurement of the elliptical surface of a wave-vector distribution in an anisotropic medium indicate that reflection and transmission still occur when the reflected and the refracted angles are larger than 90 degrees .     

Chiral molecules split light: Reflection and refraction in a chiral liquid

A light beam changes direction as it enters a liquid at an angle from another medium, such as air. Should the liquid contain molecules that lack mirror symmetry, then it has been predicted by Fresnel that the light beam will not only change direction, but will actually split into two separate beams with a small difference in the respective angles of refraction. Here we report the observation of this phenomenon. We also demonstrate that the angle of reflection does not equal the angle of incidence in a chiral medium. Unlike conventional optical rotation, which depends on the path-length through the sample, the reported reflection and refraction phenomena arise within a few wavelengths at the interface and thereby suggest a new approach to polarimetry that can be used in microfluidic volumes.     

自旋—轨道耦合下冷原子的双反射

随着中性冷原子气体的人造自旋-轨道耦合的实验实现,近年来人们开始关注与之相关的可能应用,其中包括自旋-轨道耦合下原子反射镜的研究.本文在前人研究的基础上,考虑一束自旋-轨道耦合的冷原子气体入射到有限高势垒的情形,通过将部分反射和全反射情况进行对比,发现了与之前研究不同的性质.我们发现,在全反射条件下,反射原子的极化率随入射角变化较大,而随自旋-轨道耦合强度和原子入射能量的变化较小.但在发生部分反射的情况下,反射原子的极化率不仅随入射角变化较大,随自旋-轨道耦合强度和原子的入射能量变化也十分明显.我们仔细研究了自旋-轨道耦合原子气体的反射性质并讨论了其可能的应用.     

Reflexion und Brechung an optisch einachsigen Medien in Richtung fehlender Doppelbrechung

Reflection and Refraction at Uniaxial Media in Directions of Vanishing Double Refraction The amplitude relations for the reflection and refraction of plane monochromatic waves by uniaxial media in the case of vanishing double refraction of the refracted respectively reflected waves in the uniaxial medium are obtained by a limiting process from generalized Fresnel formulae earlier derived. The incidence both from the isotropic and from the uniaxial medium is considered. The boundary conditions may be fulfilled in the case considered only by addition of refracted respectively reflected waves with amplitudes varying linearly with the distance from the boundary plane in the uniaxial medium. The requirement of vanishing double refraction restricts the possible choice of the common tangential components of all refraction vectors and consequently also of the refraction vectors of incident waves from a primarily twodimensional complex manifold to onedimensional complex manifolds, which are determined in this paper.     

Double passage analysis in random media using two-scale random propagators

In location and remote sensing experiments there arise a number of effects related to the double passage of the backscattered field through the same random inhomogeneities as the incident one. To account for the correlation of the forward-backward propagating events, there is a need for a measure in which the random information along the propagation path is preserved. For the generation of even statistical moments, the relevant measure defined in the recently formulated stochastic geometrical theory of diflraction is the two-point random function (TPRF)—a paired field measure which is propagated along the geometrical rays of the deterministic background medium. From this function all even statistical moments can be generated. Here we present an approximate analytical solution for the high-frequency propagator obtained by applying the multiscale expansion asymptotic procedure to the partial differential equation governing the propagation a1 the TPRF. The test of the solution is performed on canonical backscattering problems based on point source-point scatterer and paint source-plane mirror configurations, which justifies its further application for construction of the coherence measures of the rctrareflected field. Coherence properties of the plane and spherical wavefields reflected backward by a plane mirror were investigated. Further, we investigated the intensity enhancement effects observed in the double passage of a Gaussian beam retroreflected from a plane mirror. Asymptotic expressions lor the retroreflected intensity are obtained, and their computations show good agreement with the direct numerical evaluations.     

The mutual coherence function and the backscatter amplification effect for a reflected Gaussian-beam wave in atmospheric turbulence

The influence of a modified spectrum of refractive-index fluctuations (that includes a high wavenumber rise as well as inner- and outer-scale parameters) on the backscatter amplification effect, arising from double passage of an optical wave through statistically dependent inhomogeneities of a random medium, is studied for the case of a Gaussian-beam wave reflected by a mirror of finite size. A formal expression is first developed for the mutual coherence function, which subsequently leads to tractable analytic models for the mean irradiance in the strictly backward direction. When the inner scale and Fresnel zone are of comparable size, the modified spectrum predicts significantly larger values of the enhancement factor than predicted by the Kolmogorov power-law spectrum. It is also shown in this analysis that by varying the focal length of the mirror the enhancement effects can be greater or less than those of a plane mirror, depending on focus adjustment. All calculations are based on weak irradiance fluctuations using complex ABCD ray-matrix representations for the propagation channel and a generalized spectral representation theory for the complex phase perturbations.     

Backscattering enhancement analysis for targets in continuous random media based on wave polarization

Owing to the double passage effect, the phenomenon of backscattering enhancement arises in which the radar cross-section (RCS) in a random medium is twice that in free space. In a previous study, it was proved that the enhancement in radar cross-section (ERCS) deviates from two and has large and anomalous fluctuations, sometimes as a result of the wave polarization and other parameters, especially for targets in strong random media. Linear, including horizontal and vertical, polarizations were considered. In this paper, a numerical analysis is presented to show that the fluctuations can be reduced and make ERCS dependent almost only on the double passage effect under certain conditions. Therefore, we will have a better detection technique of targets of large sizes in continuous random media. In doing that, the linear and circular polarizations of incident waves are considered. We assume the case where a directly incident wave is produced by a line source in the far field distributed uniformly along the axis parallel to the conducting cylinder (target) axis.     

Double passage analysis in random media using two-scale random propagators

Abstract

In location and remote sensing experiments there arise a number of effects related to the double passage of the backscattered field through the same random inhomogeneities as the incident one. To account for the correlation of the forward–backward propagating events, there is a need for a measure in which the random information along the propagation path is preserved. For the generation of even statistical moments, the relevant measure defined in the recently formulated stochastic geometrical theory of diflraction is the two-point random function (TPRF)—a paired field measure which is propagated along the geometrical rays of the deterministic background medium. From this function all even statistical moments can be generated. Here we present an approximate analytical solution for the high-frequency propagator obtained by applying the multiscale expansion asymptotic procedure to the partial differential equation governing the propagation a1 the TPRF. The test of the solution is performed on canonical backscattering problems based on point source–point scatterer and paint source–plane mirror configurations, which justifies its further application for construction of the coherence measures of the rctrareflected field. Coherence properties of the plane and spherical wavefields reflected backward by a plane mirror were investigated. Further, we investigated the intensity enhancement effects observed in the double passage of a Gaussian beam retroreflected from a plane mirror. Asymptotic expressions lor the retroreflected intensity are obtained, and their computations show good agreement with the direct numerical evaluations.     

Intracavity sequential quasi-synchronous interactions in an active nonlinear medium with a regular domain structure

A theory is developed to describe sequential quasi-synchronous wave interactions in an active non-linear medium with a regular domain structure inside a cavity. In particular, sequential processes of quasi-synchronous third-harmonic generation and quasi-synchronous parametric amplification that occur in a Nd:Mg:LiNbO₃ crystal with a regular domain structure under low-frequency pumping are analyzed. The efficiency of these nonlinear optical processes is studied as a function of both the reflection coefficient of the exit mirror and the linear loss in the medium.     

Reflection and transmission coefficients of electromagnetic waves with different polarizations on a one-dimensional layer of an inhomogeneity of the medium

We have obtained strict formulas (without approximations) for the reflection and transmission coefficients of electromagnetic waves with an arbitrary polarization in an isotropic medium with a one-dimensional layer of an inhomogeneity of an arbitrary profile playing the role of a transition layer between two different homogeneous media. Since these formulas involve values that are found by numerically integrating the first-order ordinary differential equations, the result of this paper is a fast and convenient method for calculating the above coefficients. The calculated results for two particular cases are given. An analytical limiting passage from the obtained formulas to the particular case of a sharp interface between the media (i.e., to known Fresnel formulas) is presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 9, pp. 1075–1086, September, 1996.This work was supported by the Russian Foundation for Fundamental Research.     

Total reflection of waves propagating from an isotropic medium to an anisotropic medium

We examine the value n(i)/n(eff)(theta(t)) , the ratio of the indices of refraction for waves transmitted from an isotropic medium to an anisotropic medium. It is found that total reflection can occur in the case of propagation from a rarer medium to a denser medium.     

Waveguide grating mirror for large-area semiconductor lasers

We have fabricated and tested a waveguide grating mirror that uses anomalous reflection of light associated with excitation of waveguide modes. Sharp features are observed in the reflection spectra in both the wavelength and the angular domains. We confirm experimentally that, when the waveguide grating mirror is placed a short distance in front of a large-area semiconductor laser, it can control the emission spectrum. This demonstration opens a new approach to the design of very compact semiconductor lasers operating in the single-frequency-single-mode regime.