混浊介质中线偏振光和圆偏振光的后向漫散射特征

以标准的组织模型Intralipid脂肪乳溶液为研究对象,采用CCD偏振成像系统,通过测量该混浊介质的后向漫散射光的斯托克斯矢量,深入研究了不同方位的线偏振光及不同旋向的圆偏振光入射时,后向漫散射光的特征.研究结果表明：对不同的入射偏振态,后向漫散射强度、偏振度的空间分布具有方位选择性,强度和偏振度的大小随距离入射点的距离增加而减小;介质浓度增加,后向散射强度增加,偏振度减小,且同一浓度下,圆偏振光的偏振度总是高于线偏振光.     

自然光在多层介质分界面上折射时的偏振度

通过光在介质的分界面上折射时产生的偏振现象,利用非磁性介质的菲涅耳公式及入射、折射时的光强关系,从理论上详细推导了自然光在两介质分界面上折射时其偏振度的数学表达式,探讨了透射光的偏振程度与介质层数的关系.实验测试的结果表明,在考虑误差存在的情况下,实验曲线与理论曲线的变化趋势基本相符;对于同一介质,折射光的偏振度随入射角的增大而单调地增加.     

Anomalous polarization effects during light scattering in random media

The dependence of the intensity of light backscattered from a layer of a randomly inhomogeneous medium on the polarization of incident light and the size of scatterers has been investigated. The results of numerical simulation have demonstrated that the direction of rotation of the plane of polarization is different in systems with small- and large-scale inhomogeneities. It is shown for the first time that the dependence of the sign of the residual circular polarization on the size of scatterers can be observed in systems described by the Henyey-Greenstein phase function used in simulating biological tissues. A similar anomalous polarization effect, which consists in changing the direction of rotation of the plane of polarization of backscattered light with an increase in the scattering angle, is revealed in studying the coherent backscattering component. These polarization effects are observed in light backscattering from optically active media.     

The effect of the optical anisotropy of scattering media on the polarization state of scattered light

The effect of the optical anisotropy of scattering media on the polarization state of scattered light is studied. The study is performed using a simple polarization method based on the comparison of the spectral composition of the co-and cross-polarized components of transmitted light measured for samples differently oriented with respect to the plane of polarization of probe linearly polarized light. The experimental results obtained are interpreted theoretically in terms of ordinary methods used in optics of birefringent media. Using rat skin as an example, it is shown that surface tissues can be characterized by a high degree of orientational order of the local optical axis of a medium within large areas (with a size of 5 mm or more), which manifests itself in macroscopic optical measurements. In such measurements in the spectral range 550–700 nm, whole rat skin behaves as a partially depolarized phase plate with a difference between the principal refractive indices Δn ≈ 0.00023.     

Manifestation of the polarization incoherence of light in polarization self-action effects

On the basis of the beam tensor formalism proposed by F. I. Fedorov, the theory of polarization selfaction of radiation in isotropic resonant media is extended to the case of partial elliptic polarization of an electromagnetic wave. The influence of the degree of radiation polarization on the known polarization self-action effects is demonstrated and the self-polarization (depolarization) of light is predicted.     

Polarization of light and its use in various problems of optics of scattering media

As light passes through scattering media, certain specific features of the polarization of radiation manifest themselves. The paper presents materials on this problem that were obtained at the Institute of Physics of the National Academy of Sciences of Belarus over recent decades. Results of experimental investigations of media that model real objects are described for the case where the dimensionless optical parameters of media and objects coincide. A method for determining the position of a diffuse light source in the atmosphere via predominant oscillations of the light vector of scattered radiation for two directions of observation is proposed. The structure of aerosol formations (smokes, dust and liquid-droplet and crystalline clouds) is interpreted based on the character of depolarization of laser radiation sounding atmosphere. The polarization of laser radiation passing through a turbid medium and reflected from it is studied. Practical applications are proposed. Fundamentals of an applied vector theory of radiation transfer, which made it possible to considerably expand notions of light scattering in strongly turbid media, are given. Studies of light propagation in encapsulated liquid crystals, which are used for solving of a large number of problems, are described. In these objects, ordinary and extraordinary rays that arise in crystals under electric voltage can give rise to a wave that is attenuated to a different degree and whose phase and polarization characteristics are varying.     

Coherent recovery of the degree of polarization of light propagating in random anisotropy media

We report on the study of light polarization behavior in random anisotropy scattering media. It is shown that, in the case of low scattering events, the degree of polarization (DOP) demonstrates oscillatory behavior due to the coherent character of light scattering. A strong increase in the DOP is demonstrated by using electro-optic fine tuning of the refractive index modulation depth of the scattering media.     

Residual polarization of non-coherently backscattered linearly polarized light: the influence of the anisotropy parameter of the scattering medium

The effect of preservation of the residual polarization of backscattered light in the case of multiply scattered disordered media illumination by a linearly polarized plane wave is examined using the path-integral approach and Monte Carlo simulation. Disordered ensembles of non-interacting dielectric particles are considered as the model of scattering media. The influence of the anisotropy parameter of the scattering system on the degree of residual polarization is analysed. Experimental results obtained for various scattering systems at different wavelengths of illuminating light are in satisfactory agreement with the results of theoretical analysis and Monte Carlo simulation. The dependence of statistical properties of the polarization states of backscattered field partial components, such as probability distributions of ellipticity, on the anisotropy parameter is studied.     

Polarization preservation in diffusive scattering from in vivo turbid biological media: effects of tissue optical absorption in the exact backscattering direction

There is considerable recent interest in using polarized light to investigate turbid biological media. Although tissue multiple scattering randomizes incident polarization states, there are circumstances when appreciable degree of polarization can be observed in diffusive scattering. In this study, we use polarization modulation and synchronous detection to examine in the exact backscattering direction the polarization properties of diffusely reflected visible light from hands of human volunteers of varying pigmentation levels. The surviving polarization fraction increases with increasing pigmentation, likely due to preferential loss of highly scattered, long-pathlength photons; this mechanism lowers the average pathlength traversed by the detected light and hence increases the measured polarization preservation. This behavior is contrasted with the overall diffuse reflectance intensity, whose magnitude decreases with increasing absorption. These experiments demonstrate the important influences of medium optical properties on the polarization characteristics of multiply scattered light, which must be further investigated to enable quantitative polarization evaluation of turbid media such as biological tissues.     

Electrically-Controllable Liquid Crystal Polarizing Filter for Eliminating Reflected Light

A high-speed controllable polarizing filter has been developed to eliminate obstructive polarized light reflected from glass and watery surfaces for image pickup in video media program producing and marine dynamic remote sensing. In this device, the polarization plane of incident light is rotated through 0°, 45°, 90° or 135° by an electrically-controllable polarization rotator composed of 45° and 90° twisted nematic liquid crystal cells, and the polarization component of reflected light is absorbed by a fixed polarizing film. It selectively absorbs more than 80% of incident white light linearly polarized in an arbitrary direction. With the drastic reduction of reflected light, the object images hidden by the bright reflected light are clearly captured in real time. Another type of polarizing filter, using a guest-host liquid crystal cell instead of the polarizing film, controls light absorption as well as polarization angle.     

Some features of the polarization characteristics of strongly absorbing helical periodic media

Results are presented on the polarization characteristics (rotation of the plane of polarization and polarization ellipticity) as a function of the layer thickness and the absorption anisotropy in strongly absorbing media having a helical structure. A strong resonancelike change in the polarization ellipticity is found as a function of the anisotropy of the absorption at frequencies of diffractional interaction of the light with the medium. A change in the sign of rotation of the plane of polarization of the light is observed as the layer thickness is varied. It is established that sign of the rotation also changes as the absorption anisotropy varies. These effects are studied under conditions of interaction of light with a half space and with a layer of medium of finite thickness. Some new features are identified in the previously observed effect wherein the absorption of radiation in media having a periodic structure decreases as the layer thickness increases. Zh. Tekh. Fiz. 69, 72–78 (August 1999)     

Determination of the depth-resolved Stokes parameters of light backscattered from turbid media by use of polarization-sensitive optical coherence tomography

Polarization-sensitive optical coherence tomography (PS-OCT) was used to characterize completely the polarization state of light backscattered from turbid media. Using a low-coherence light source, one can determine the Stokes parameters of backscattered light as a function of optical path in turbid media. To demonstrate the application of this technique we determined the birefringence and the optical axis in fibrous tissue (rodent muscle) and in vivo rodent skin. PS-OCT has potentially useful applications in biomedical optics by imaging simultaneously the structural properties of turbid biological materials and their effects on the polarization state of backscattered light. This method may also find applications in material science for investigation of polarization properties (e.g., birefringence) in opaque media such as ceramics and crystals.     

The Imbert-Fedorov shift of paraxial light beams

We present a solution to the problem of reflection and transmission of a polarized paraxial light beam at an interface between two homogeneous media by using a two-form amplitude and an extension matrix to represent the vectorial angular spectrum of a three-dimensional (3D) light beam. We derive general formulas for the Imbert-Fedorov (IF) shift of the reflected and transmitted beams of a polarized paraxial light beam. The IF shift of two different types of polarized beams is calculated, and the influence of the polarization state and the polarization feature of the vectorial angular spectrum on the IF shift is discussed.     

Polarization visualization of scattering media with CW laser radiation

The method of polarization visualization of a multiply scattering medium containing macroinhomogeneities based on analysis of polarization spatial distribution of a scattered linearly polarized light is discussed. The treatment is based on statistical properties of the effective optical path distribution of scattered field components. The influence of media scattering properties and the geometry of the experiment on the inhomogeneity image contrast obtained with use of polarization degree and of normalized scattered intensity of radiation as visualization parameters are discussed, as well as spatial resolution achieved in these both cases. Using the results of theoretical analysis and of the experimental model, the relationship between the shapes of spatial distributions of polarization degree and the intensity of the scattered light is considered as a function of the position of the visualized object (an absorbing half-plane immersed in a plane layer of the scattering medium). The opportunities for enhancing the quality of the images formed in this way are also discussed.     

Role of Light Polarization in the Optothermal Effect

It is shown that the highest optothermal effect in low-intensity irradiation is attained on chromophores of stationary orientation exposed to irradiation by a linearly polarized light. For chromophores with stochastization of orientation between the events of light absorption, the magnitude of the optothermal effect is independent of polarization and is three times lower than in stationary orientation. In anisotropic media, an optimally oriented linearly polarized light is more efficient.     

Interaction of laser radiation with an axially symmetric polarization with condensed media

The interaction of laser radiation with an axially symmetric polarization with condensed media is studied theoretically. The interaction results in the formation of ordered micro- and nanoscale structures that can be described in terms of the universal polariton model of laser-induced media damage. It is shown that the radially polarized radiation induces a periodic ring resonance grating that focuses the excited surface plasmon-polaritons, thus increasing the total light intensity in the center of the irradiated zone.     

Optical manifestations of planar chirality

We report that planar chiral structures affect the polarization state of light in a manner similar to three-dimensional chiral (optical active) media. In experiments with artificial metal-on-silicon chiral planar gratings of 442 wallpaper group symmetry, containing millions of chiral elements per square centimeter, we observed rotation of the polarization azimuth in excess of 30 degrees of light diffracted from it. The rotation was found to change its sign for two enantiomeric forms of the media and to have components associated with both the structural arrangement and the chirality of individual structural elements.     

Polarization plane's weak rotation amplifiers and polarization azimuth stabilizers

A simple and effective method to measure an electromagnetic wave polarization plane's weak rotations in various media is proposed. The specific features of the polarization plane's rotation amplification for the light reflection and transmission through the absorbing and amplifying isotropic layers are calculated. The amplification effects on an anisotropic and cholesteric liquid crystal (CLC) layers are also considered. In conclusion the question of probable choice of the amplifier's noise/signal ratio is discussed.     

Single layer homogeneous model for surface roughness by polarized light scattering

In this paper a homogeneous single layer model for surface roughness by polarized light has been developed. It has been shown that the reflectance change in non-absorbing layer is directly proportional to the refractive index of the ambient and substrate media for s polarization but inversely proportional to the p polarization and it is directly proportional to the square of the thickness of the layer for both the polarization. In an absorbing layer, it has been shown that the thickness of the layer is equal to the twice of surface roughness of the single layer identical system for s polarization but it is ratio of twice of surface roughness to the square of refractive index of thin film for p polarization. The extinction coefficient of the layer is directly proportional to the thickness of that layer for both the polarization. The consequence of the scattered light on the specular reflectance and transmittance for oblique incidence shows that there is reduction in reflectance (in both non-absorbing and absorbing cases) and transmittance (in the absorbing case for p polarization only), due to roughness on the surface under the Drude effective-medium approximation. Thus such an absorbing layer provides a valid model for the effect of scatter on the transmittance for p polarization only.     

Generation of quadrature-squeezed light during the propagation of a light wave in a birefringent fiber

It is shown that generation of quadrature-squeezed states of a vector electromagnetic field in which quantum fluctuations in one of the quadrature components are smaller than in the coherent state can occur in cubically nonlinear media (birefringent fibers) with efficient energy transfer between the polarization modes of the field. It is shown that for certain distributions of the initial total power between modes, light with suppressed quantum fluctuations in both polarization modes of the vector field is formed at the fiber exit. The optimal conditions for obtaining quadrature-squeezed light are determined. New analytical expressions are obtained for the degree of squeezing in the two polarization modes in the case when there is no energy transfer between the polarization components of the field propagating in the fiber (eigenmodes of two-wave mixing).