Multiple scattering of elliptically polarized light in two-dimensional medium with large inhomogeneities

For elliptically polarized light incident on a two-dimensional medium with large inhomogeneities, the Stokes parameters of scattered waves are calculated. Multiple scattering is assumed to be sharply anisotropic. The degree of polarization of scattered radiation is shown to be a nonmonotonic function of depth when the incident wave is circularly polarized or its polarization vector is not parallel to the symmetry axis of the inhomogeneities.     

不同波长的散射介质后向散射光偏振度特性

基于Stockes矢量,通过测量以线偏振光和圆偏振光入射时脂肪乳剂后向散射光的偏振度,研究了532nm、650nm和780nm三个波长的光与散射粒子粒径为325nm的脂肪乳剂溶液作用后,其后向散射光的偏振度特性.研究结果表明,对于入射线偏振光,780nm波长后向散射光中的线偏振光成分多于圆偏振光成分,而532nm波长则相反;对于入射圆偏振光,三个波长后向散射光中的圆偏振光成分均多于线偏振光成分;532nm波长的总偏振度高于650nm和780nm两个波长各自的总偏振度;线偏振光的保偏性优于圆偏振光的保偏性,但偏振光在散射介质中的穿透深度较小.因此,后向散射成像技术适用于物体表层成像,而且选择波长略大于粒径的线偏振光可以提高成像质量.     

不同波长的散射介质后向散射光偏振度特性

基于Stockes矢量,通过测量以线偏振光和圆偏振光入射时脂肪乳剂后向散射光的偏振度,研究了532 nm、650 nm和780 nm三个波长的光与散射粒子粒径为325 nm的脂肪乳剂溶液作用后,其后向散射光的偏振度特性.研究结果表明,对于入射线偏振光,780 nm波长后向散射光中的线偏振光成分多于圆偏振光成分,而532 nm波长则相反;对于入射圆偏振光,三个波长后向散射光中的圆偏振光成分均多于线偏振光成分;532 nm波长的总偏振度高于650 nm和780 nm两个波长各自的总偏振度;线偏振光的保偏性优于圆偏振光的保偏性,但偏振光在散射介质中的穿透深度较小.因此,后向散射成像技术适用于物体表层成像,而且选择波长略大于粒径的线偏振光可以提高成像质量.     

Backscattering of linearly and circularly polarized light in randomly inhomogeneous media

The scattering of linearly or circularly polarized light from a semibounded randomly inhomogeneous medium is considered. A new technique for simulating the electromagnetic radiation transport using the Monte Carlo method is proposed, which makes it possible to avoid cumbersome calculation of Muller matrices. Expressions are obtained for the co- and cross-polarized components of backscattered light for incident light of arbitrary polarization. The coherent and incoherent backscattering components are calculated for arbitrary combinations of incident and scattered light polarizations. It is shown that the main contribution to coherent backscattering is from the co- and cross-polarized components for linearly and circularly polarized light, respectively. The backscattering from an optically active random medium is calculated.     

生物组织多光谱偏振特性研究

生物组织内部结构复杂且具有较强的散射特性,而光作为生物组织检测的重要信息载体,其自身特性包括颜色、幅值、偏振等都对信息获取有较大的影响.结合偏振成像,对生物组织多光谱偏振特性展开了研究,依据不同微粒尺寸的分布建立了均匀单层生物组织模型,结合瑞利和米氏散射理论模拟了基于单个微粒的两种散射事件.瑞利散射具有较好的前向后向散...     

Inelastic electron scattering from a Coulomb potential in a laser field

We present a theoretical study of inelastic electron scattering from a fixed Coulomb potential in the presence of a laser field, based on analytic expressions for the two-photon continuum-continuum transition matrix element. We present here the particular case of incident and scattered light polarizations orthogonal to each other and to the incident electron momentum. Results are given for the cross sections corresponding to the detection of electrons and polarized photons in coincidence, and for the detection of polarized photons only.     

Dependence of the circular polarization of backscattered light in random media on anisotropy of scatterers

The scattering of linearly or circularly polarized light from a semi-infinite randomly inhomogeneous medium is considered. Using the Monte Carlo method, it is shown that, in the case of a wide front of incident and scattered optical radiation and irrespective of the degree of scattering anisotropy, the copolarized component of backscattered light dominates the cross-polarized component for the linear polarization and the cross-polarized component dominates the copolarized component for the circular polarization. If the beams of incident and scattered radiation are spatially separated and the size of scatterers exceeds the wavelength, the circular copolarized component dominates the cross-polarized one. A similar effect of the change in direction of the rotation of the plane of polarization in relation to the size of scatterers is revealed for pulsed radiation.     

非球形粒子散射光的去偏振特性研究

目标对入射偏振光的散射特性反映了目标的属性信息。在Rayleigh散射理论的基础上，通过单层非球形粒子对入射偏振光的散射数学模型，应用矢量传输方程来计算非球形粒子散射的Mueller矩阵元，求解散射介质的偏振度，讨论在不同介质层厚度、粒子半径和探测角的条件下，非球形粒子散射光去偏振度的变化特性，给出了模拟仿真结果。该方法为研究目标的内部结构、厚度和粗糙度等特征以及目标的探测和识别提供了一种新的途径。     

Interaction of ultrashort elliptically polarized laser pulses with nonlinear helical photonic metamaterial

The effect of nonlinear properties of a material with a periodic structural cell (three-dimensional spiral) on the specificity of transmission and reflection of elliptically polarized laser pulses normally incident on the metamaterial is studied using the finite-difference time-domain method. An analysis of the hodograph of electric-field strength vector showed that an increase in the peak intensity of a linearly polarized laser pulse incident on a sample leads to an increase in the orthogonal component of the electric-field strength vector in the pulse transmitted through the medium. When pulses containing few electric-field periods are incident on a metamaterial, the latter demonstrates radically different optical properties for right- and left-handed circularly polarized light passing through the medium. It was shown that an increase in the intensity of a right-handed (left-handed) circularly polarized ultrashort pulse, incident on a sample composed of a rather large number of right-handed (left-handed) spirals made of nonlinearmaterial, widens the frequency range within which the incident light is almost entirely reflected from the medium.     

光学元件亚表面缺陷偏振双向反射分布函数

 利用琼斯散射矩阵,借助右手正交基组来表示入射场和散射场,推导出光学元件亚表面缺陷或微粒在不同偏振状态下的双向反射分布函数的表达式。给出了亚表面缺陷在不同入射角条件下,不同偏振状态下的双向反射分布函数与散射方位角之间的关系,以及不同入射角下p偏振入射产生的p偏振双向反射分布函数的3维散射图。结果表明:p偏振入射产生的p偏振双向反射分布函数强烈依赖于入射角、散射角和方位角,且随着入射角的增加,其最小值点所对应的方位角逐渐减小。     

动态光散射实验中散射光偏振状态的研究

颗粒散射光的偏振状态对提高动态光散射实验系统空间相干性和测量结果正确性有着重要影响,因此研究散射光的偏振状态具有重要现实意义的。本文利用米散射理论分析了入射光与散射光偏振状态之间的关系,在此基础上揭示了在动态光散射中使用垂直偏振光作为入射光的理论依据,并在实验中验证了上述理论的正确性。     

A Monte Carlo approach for the calculation of polarized light: application to an incident narrow beam

Monte Carlo approaches to compute multiple scattering of polarized light are examined. A Backward Monte Carlo (BMC) method is developed to solve the Stokes vector of the multiple scattered light for an inhomogeneous scattering medium with boundaries. A generalized form of the BMC method in vector notation is proposed. This method can determine the scattered light with sufficient accuracy in both intensity and polarization compared to the same calculation using the doubling-adding method for a plane parallel medium.For application to a narrow incident beam and an inhomogeneous medium, a modified BMC method is developed, borrowing a concept from the Forward Monte Carlo (FMC) method for the first scattering events. Furthermore, a modification of the total scattering matrix, i.e., the combination of the derived scattering matrix with its time inverse, is discussed. This BMC method can be used successfully for model calculations of lidar and other laser measurements of polarized light.     

Controllable and switchable chiral near-fields in symmetric graphene metasurfaces

A strong chiral near-field plays significant roles in the detection, separation and sensing of chiral molecules. In this paper, a simple and symmetric metasurface is proposed to generate strong chiral near-fields with both circularly polarized light and linearly polarized light illuminations in the mid-infrared region. Owing to the near-field interaction between plasmonic resonant modes of two nanosheets excited by circularly polarized light, there is a strong single-handed chiral near-field in the gap between the two graphene nanosheets and the maximum enhancement of the optical chirality could reach two orders of magnitude. As expected, the intensity and the response wavelength of the chiral near-fields could be controlled by the Fermi level and geometrical parameters of the graphene nanosheets, as well as the permittivity of the substrate. Meanwhile, based on the interaction between the incident field and scattered field, the one-handed chiral near-field in the gap also could be generated by the linearly polarized light excitation. For the two cases, the handedness of the chiral near-field could be switched by the polarized direction of the incident light. These results have potential opportunities for applications in molecular detection and sensing.     

Scattering of electromagnetic wave by perfect electromagnetic conductor (PEMC) sphere placed in chiral media

A theoretical investigation has been carried out for electromagnetic waves scattering from a perfect electromagnetic conductor (PEMC) sphere which is placed in chiral media. The formulation of the problem is realized by expanding the incident as well as the scattered electromagnetic fields in terms of left circularly polarized (LCP) and right circularly polarized (RCP) waves. By applying the boundary conditions at the chiral-PEMC interface, eight simultaneous equations are generated, which yield the scattering coefficients associated with the Left and Right electromagnetic waves. The relative contribution of Co-polarized and Cross-polarized components of fields to the calculations of scattering cross-section is presented. The effect of admittance parameter and the effect of chirality parameter in cases of lossless, lossy permittivity and lossy permeability on Co and Cross components of scattering cross sections are observed. The results are also compared with available published literatures which are in good agreement.     

Theory of polarization phenomena in the hyper-Raman effect

This paper describes a general theory of the polarization state of hyper-Raman emission. In particular an examination is made of the azimuth and ellipticity of hyper-Raman scattered radiation relative to that of a general elliptically polarized source.

It is shown that a distinction may be made between infra-red active and inactive vibrations in the hyper-Raman effect by an analysis of the ellipticity of the scattered light. For a circularly polarized source, the scattering from infra-red inactive vibrations exhibits full reversal of circularity; infra-red active vibrations scatter with no change in circularity. In hyper-Rayleigh scattering a similar analysis is given for non-polar and polar molecules.     

多光子非线性Compton散射对等离子体中颗粒成长的影响

应用等离子体颗粒成长模型和多光子非线性Compton模型,研究了多光子非线性Compton散射对等离子体中颗粒成长的影响。提出了将入射光和多光子非线性Compton散射光作为颗粒成长的新机制,对颗粒凝合截面、凝合系数、颗粒收集的电子流和离子流的表达式进行了修正。结果表明,等离子体参数的变化与多光子非线性Compton散射成分、电子散射前的初始速度、入射角、与电子同时作用的光子数等因素有关。散射使生长过程中收集离子机制和凝合机制增强,颗粒的凝合截面增大,颗粒半径较快的非均匀增长。     

Synchronization of optical polarization conversion and scattering in chiral fibers

We demonstrate that polarization transformation and scattering in adiabatically twisted single-mode birefringent optical fibers is synchronized so that light in one evolving elliptically polarized mode is freely transmitted while orthogonally polarized light is scattered out of the fiber. Thus, linearly polarized radiation initially oriented along the fast axis of the untwisted fiber is transformed to circularly polarized light with the same sense of rotation as the twisted fiber and is scattered out of the fiber. When the fiber twist is first accelerated and then decelerated, the fiber becomes a broadband, low-insertion-loss, linear polarizer.     

表面上方微粒及微粗糙度偏振光散射特性

为了区分由表面上方微粒和表面微粗糙度两种散射机理引起的散射光,利用偏振双向反射分布函数,并借助于由,■,■组成的正交右手基组表示了入射电场和散射电场。从理论上给出了两种不同散射机理在不同偏振状态下的双向反射分布函数与入射面外方位角之间的变化关系,并通过对这两种散射机理下的偏振双向反射分布函数的比较发现,利用p偏振入射产生的p偏振散射光(BRDFpp)可以将表面上方微粒和表面微粗糙度两种散射机理区分开来。     

Theory of compton scattering of polarized photons by a polarized particle with spin 1/2

Formulas are obtained for the differential effective scattering cross section when elliptically polarized photons are scattered by a point, initially stationary, a polarized Dirac particle possessing a charge, and an anomalous magnetic moment. The cases in which the incident radiation is unpolarized, linearly polarized, and circularly polarized are analyzed.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 8, pp. 121–128, August, 1968.In conclusion we thank Professor A. A. Sokolov for suggesting this problem.     

Raman optical activity comes of age

The theory and applications of Raman optical activity (ROA), which measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or, equivalently, a small circularly polarized component in the scattered light, are briefly reviewed. Thanks to new developments in instrumentation, ROA may be applied to a wide range of chiral molecular species. As well as providing the absolute configuration of small chiral molecules, the application of ab initio methods to the analysis of experimental ROA spectra holds great promise for the determination of the three-dimensional structure and conformational distribution in unprecedented detail. The many structure-sensitive bands in the ROA spectra of aqueous solutions of biomolecules provide detailed structural information including, in the case of proteins, the tertiary fold in addition to secondary structure elements such as helix and sheet. ROA studies of unfolded and partially folded proteins are providing new insight into the residual structure in denatured proteins and the aberrant behaviour of proteins responsible for misfolding diseases. It is even possible to measure the ROA spectra of most intact viruses, from which information about the folds of the major coat proteins and the structure of the nucleic acid core may be obtained. Hopefully this review will stimulate interest in the molecular physics aspects of the subject, and will encourage further theoretical work aimed at extracting maximum information from the plethora of structure-sensitive bands in typical ROA spectra.