The effect of a local field on Raman scattering in a uniaxial crystal

This paper discusses the Raman scattering of light in an anisotropic crystal in the crystal optics approximation, taking into account local fields acting on the molecules. It shows that the effect of the local field reduces to the introduction of the effective Raman polarizability tensor of the molecules, which depends both on the properties of the molecules themselves and on the characteristics of the crystal at the frequencies of the incident and scattered waves. Raman scattering cross sections are obtained in a uniaxial crystal for various types of incident waves. It is shown that, in the case of an extraordinary incident wave, the local field substantially affects how the cross section depends on the direction of incidence. Zh. éksp. Teor. Fiz. 112, 180–191 (July 1997)     

Generation of a continuum and stimulated Raman scattering harmonics during scattering of electromagnetic radiation of relativistic intensity

A theory of the propagation instability of plane, monochromatic, circularly polarized electromagnetic waves of relativistic intensity in matter is developed for a spatially three-dimensional geometry including arbitrary polarization of the scattered radiation. Harmonic generation owing to striction and relativistic nonlinearity is examined, as well as scattering owing to electron recoil, the decay instability of the harmonics with formation of scattered electromagnetic waves (Stokes components of the stimulated Raman scattering and plasmons), the interaction of electromagnetic waves in the plasma (antistokes stimulated Raman scattering), and the generation of a radiative continuum. The transition of the three-dimensional theory to a one-dimensional problem in the nonrelativistic limit is discussed. Zh. éksp. Teor. Fiz. 113, 2034–2046 (June 1998)     

Angular dependence of Raman scattering selection rules for long-wavelength optical phonons in short-period GaAs/AlAs superlattices

The angular dependence of Raman scattering selection rules for optical phonons in short-period (001) GaAs/AlAs superlattices is calculated and experimentally studied. Experiments are performed using a micro-Raman setup, in the scattering geometry with the wavevectors of the incident and scattered light lying in the plane of superlattices (so-called in-plane geometry). Phonon frequencies are calculated using the Born model taking the Coulomb interaction into account in the rigid-ion approximation. Raman scattering spectra are calculated in the framework of the deformation potential and electro-optical mechanisms. Calculations show an angular dependence of the selection rules for optical phonons with different directions of the wavevectors. Drastic differences in the selection rules are found for experimental and calculated spectra. Presumably, these differences are due to the Fröhlich mechanism in Raman scattering for short-period superlattices.     

沙尘气溶胶粒子群的散射和偏振特性

根据Mie散射理论,以对数正态分布函数描述沙尘气溶胶粒子群的粒径尺度分布,计算了沙尘气溶胶粒子群在0.2～40μm波段间对太阳短波辐射和地球大气长波辐射的单次散射反照率、散射相矩阵函数,揭示了不同相对湿度时,沙尘粒子群对入射辐射的散射和偏振的特征。结果表明,沙尘粒子群的单次散射反照率随着入射波长的增加有较大起伏,不同相对湿度条件下,变化趋势基本一致;在可见光、近红外波段单次散射反照率随湿度增加而变大,湿度95%时非常接近于1;大于10μm的热红外波段单次散射反照率随相对湿度增加而减小,具有较强的吸收辐射能力。散射辐射强度受湿度影响较小,随散射角的增加呈现先减小后增大的趋势,且增大的趋势随着波长的增加而减弱;不同波段上,线偏振和圆偏振随散射角和相对湿度变化存在差异;在前向和后向仅对入射辐射为圆偏振辐射产生圆偏振散射;散射光的偏振特性及其湿度差异主要表现在后向散射区,多以拱形形式体现。拱顶峰值散射角位置存在差异,且峰值散射角随相对湿度的降低向后向漂移。     

Fundamental Studies of Stimulated Raman Scattering and Adaptive Optics on the Basis of Stimulated Light Scattering

Some results associated with the fundamental investigations of stimulated scattering of light in various media are reported. A number of problems of adaptive optics based on stimulated scattering is studied. Concrete results of experimental investigations of physically important characteristics of conventional (spontaneous) and stimulated Raman scattering are presented and discussed. Among them are the scattering indicatrix and the relations between the phases of laser radiation incident on a substance and stimulated scattering. These results were first obtained in the G. S. Landsberg Optical Department of the P. N. Lebedev Physical Institute of the Russian Academy of Sciences. Data on excitation sources and the radiation detection technique are systematized. The main characteristics of spontaneous Raman scattering and forward and backward stimulated Raman scattering (energy parameters, pulse duration, pulse shape, divergence, brightness, spectral width, far- and near-field intensity distributions) are presented. The results on dynamic holography, phase conjugation of light in stimulated scattering, and reconstruction and recording of information (images) with the help of amplifying dynamic holograms are presented. The physical mechanisms responsible for the interference field recording and the phase conjugation of pump radiation in stimulated light scattering are discussed. The data on phase conjugation for stimulated scattering excited by picosecond optical pulses and the results associated with the effect of excitation geometry on the optical phase conjugation in the case of stimulated scattering excited by nanosecond pulses are presented.     

Diagnostics of skin pathologies based on spectral analysis of backward and raman scattering

A mathematical model of the interaction of optical radiation with skin tissues is developed taking into account stimulated Raman scattering. Numerical experiments show that the backscattering spectra possess specific features typical of skin pathologies. It is shown that the pathology type can be determined from an analysis of the differential ratios of the Raman scattering intensities at 1271 and 1663 cm^?1 to the intensity in the region of 1454 cm^?1. It is found that the difference in the differential ratios of the Raman scattering intensities for pathologically changed and normal layers may exceed 40%.     

Stimulated scattering of electromagnetic waves in a magnetised plasma

We present estimates of threshold powers, growth rates and amplification factors for stimulated scattering of electromagnetic waves off electrostatic modes in a magnetized plasma, The magnetic field strength is assumed to influence only the electrostatic modes and not the propagation of incident and scattered electromagnetic waves.     

光纤中受激拉曼散射连续谱研究

我们在实验中研究了自相位调制效应和受激四光子混频效应对受激拉曼散射光谱的影响。在较强的泵浦光和适当的入射条件下,得到九阶受激拉曼散射的级联 Stokes 连续平滑谱带,带宽3500cm~(-1),其强度可与530nm 泵浦光强相比拟。     

Optical properties in photoelectron diffraction theory

Photoelectron diffraction effects may be strongly influenced by optical properties of the solid. Due to refraction and absorption of light at a surface, the state of polarization of light may be changed and, therefore, the corresponding photoelectron diffraction intensity. In order to include optical properties of solids in photoelectron diffraction theory, a general polarization vector of light is defined taking into account both refraction and absorption of light at the vacuum–solid boundary. In a first step, the radiation field of light inside the solid is approximated macroscopically according to classical electrodynamics. Analytical expressions are derived within a real-angle representation of Fresnel equations to reveal the influence of refraction and absorption of light on the state of polarization of light. A general refractive index in dependence on the incident angle of light is introduced which determines the refractive angle inside the solid (refraction law with real angles) and the order of influence of absorption of light. The general polarization vector is applied in the calculation of dipole transition matrix elements in a multiple-scattering cluster model of photoelectron diffraction, where the process of photoabsorption (dipole transition matrix element) and multiple scattering processes of photoelectrons (scattering path operator) are considered separately. Different analytical and numerical results of photoelectron diffraction effects are presented for light of general polarization incident at general angles taking into account the optical properties of the solid. Examples are shown and discussed in detail for Cu(001) and GaAs(110) surfaces.     

伴随自聚焦的受激布里渊散射相位共轭研究

在聚焦激发方式下,当不均匀泵浦光场包含一个还发生自聚焦的强分量时,受激布里渊散射仍能产生高质量的共轭波。散射波这时完全发自自聚焦所形成的亮丝区域。共轭比η依赖于强分量和总入射光的强度之比σ,并在0<σ<1间区某处形成一极大值η_max(=80％)。借助“光纤”集光的细丝模型计算了自聚焦对η(σ)的影响,得到同实验圆满一致的结果。 关键词：     

Inelastic light scattering by electrons and plasmons in metals

The cross section of the inelastic light scattering by electron-hole plasma in metals is studied. The Coulomb interaction of electron excitations is taken into account self-consistently. The system of the Boltzmann equation for electronic fluctuations and Maxwell’s equations for the interaction field is solved. The Raman spectra consist of the electron-hole background, diffuson and plasmon resonances. The widths of this background and resonance are determined by the electron collision rate as well as by the decay of the incident and scattered radiation in the metal. The line shape depends on the screening of the electron-light interaction, i.e., on the incident radiation frequency. Zh. éksp. Teor. Fiz. 112, 679–689 (August 1997) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Cooperative effects in Raman scattering

We formulate a theory of Raman scatterings from molecules based on the idea that the molecules within a small portion of the wavelength of the incident light should be considered as a single quantum-mechanical system. In such a system, if the final level involved in the Raman scattering is populated by the stimulated absorption or earlier scattering, the theory predicts that the scattering cross section would be increased approximately by a factor of the number of molecules existing in this final scattering level.     

Clebsch-Gordan coefficients and two-phonon resonance Raman scattering in cubic crystals

The intensity of two-phonon resonance Raman scattering in cubic crystals is expressed in terms of Clebsch-Gordan coefficients. A plot of the scattering intensity against the direction angles of the polarization vectors of the incident and scattered radiation is obtained. Several useful polarization relations are obtained for the scattering intensities in experiments with different geometries.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 75–80, August, 1978.     

Theory of Raman scattering in Europium-chalcogenides

The intensity of the spin assisted Raman scattering in the Eu-chalcogenides is calculated using the excited states which were used in the analysis of the optical absorption. Various mechanisms are examined for the Raman scattering. In these mechanisms, the cross effect of the 4f spin-orbit interaction and the exciton-phonon interaction is found to be the most important for the scattering intensity. The characteristics of the Raman scattering from this mechanism are as follows: When the frequency of the incident light is in the tail region of the absorption peak, the polarization of the scattered light is perpendicular to that of the incident light; when the light in the middle region of the absorption peak is applied, the polarization of the incident light is depolarized in the scattered light; the scattering intensity decreases when the spin fluctuation is suppressed by an application of magnetic field or by lowering temperature through the Curie temperature. These characteristics in the Raman scattering have been observed in the experiments.     

Generation of Raman polaritons in three-level atomic media

A theory of formation of Stokes field (Raman) polaritons, which arise due to the coherent stimulated Raman scattering of light in an ensemble of three-level atoms placed in a Fabry-Perot cavity in the case of a strong coupling regime, is developed. The dispersion and absorption properties of Raman polaritons are investigated and the conditions for polariton amplification are found. It is shown that for certain pump power values, nonclassical correlations (entanglement) between light and dark polaritons are observed in the system.     

Optical properties of pigmented coatings taking into account particle interactions

A T-matrix approach is used to obtain the orientation-averaged scattering and absorption cross sections of randomly oriented particle clusters, and the average angular distribution of the radiation scattered by them. The coefficients involved in the expansion of the phase function are obtained from this T-matrix approach, and used in a multiple scattering formalism to characterize the angular distribution of the diffuse radiation propagating through a particulate coating perpendicularly illuminated with collimated visible radiation. Asymmetry between forward and backward propagating diffuse radiation intensities is taken into account by means of this multiple scattering approach, which is based on solving the radiative transfer equation for successive scattering order contributions. A four-flux model is applied to compute the reflectance in terms of wavelength of the incident radiation and particle concentration. An application of the formalism is carried out to predict the optical properties of titanium dioxide pigmented polymer coatings, in terms of the pigment volume fraction and the degree of aggregation.     

罗丹明B荧光增强苯受激拉曼散射研究

将液芯光纤技术与荧光增强受激拉曼散射技术相结合,能够大大增强受激拉曼散射光谱强度,降低受激拉曼散射阈值。通过对罗丹明B苯溶液在液芯光纤中的受激拉曼散射进行研究,结果表明:荧光染料Rhodamine B可以降低苯溶液的各阶受激拉曼散射阈值近一个数量级;在一定浓度范围内(10-6mol/L~10-8mol/L)各阶Stokes阈值随浓度降低而降低,并在理论上给出了解释。并且理论推导了在荧光种子作用下的四阶耦合波方程。液芯光纤中的受激拉曼光谱技术在对实现宽带受激辐射激光器、种子激光,以及生物大分子结构研究、生物分子的非生物过程研究等领域等有光明应用前景。     

Relationship between cross section and matrix normalization of polarized radiation scattering

A simple relationship between the total scattering cross section and the normalizing constant of the scattering matrix for the general case of an arbitrary scattering particle and elliptically polarized incident radiation is obtained. The polarized radiation is described by the Stokes parameters I, Q, U, V. The obtained relationship is a consequence of two forms of energy conservation. The first one is in terms of the total scattering cross section. The other one involves the normalizing constant of the scattering matrix. The obtained relationship contains dimensionless integrals of the radiation scattered over all directions of scattering. The integrals depend on the elements of the first row of the scattering matrix and on the relative values of the Stokes parameters of the incident radiation. In the case of cross section, the incident radiation is assumed to be a plane wave. In the case of normalization constant, the incident radiation is assumed to be a convergent beam. The possible dependence of the scattering integrals on specificities of the particle illumination is taken into account in the obtained relationship. The relationship may be helpful in the various cases. So, the relationship allows one to determine any of the two characteristics of the scattering process under investigation, cross section or normalizing constant, via the other one. The relationship can be used for obtaining the scattering integrals and for analyzing the influence of the incident radiation polarization on cross section and normalizing constant.