Backscattering target detection in a turbid medium by use of circularly and linearly polarized light

The polarization properties of the backscattered light from a turbid medium containing large-diameter (10.143-microm) and small-diameter (0.202-microm) spherical polystyrene particles are studied. It is shown that the difference in the polarization properties of the emerging light that originates at the target and that is backscattered from the medium allows for improvement of image contrast by use of polarized light. Based on the images obtained by the CCD camera, the polarization memory effect with circularly polarized light is demonstrated to have an advantage over the linear polarization technique in imaging a highly reflective target inside a turbid medium containing large particles.     

Backscattering of circularly polarized pulses

Using numerical simulations of vector radiative transport, we examine time-resolved backscattering of circularly polarized plane waves normally incident upon a slab containing a random distribution of latex spheres in water. For large spheres the effect of polarization memory occurs a short time after first-order scattering and before depolarization. It is the result of successive near-forward-scattering events that maintain the incident wave's helicity. For moderately large scatterers it exhibits a simple dependence on the anisotropy factor. For larger spheres or those with higher refractive indices, it also depends on complicated angular and polarization characteristics of backscattering given by Mie theory.     

Backscattering of a wave in layered regularly and randomly inhomogeneous media

Pacific Ocean Oceanological Institute, Far Eastern Branch, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1079–1083, September, 1989.     

Time-resolved backscattering of circularly and linearly polarized light in a turbid medium

Time-resolved backscattering profiles of circularly and linearly polarized light were measured from a turbid medium composed of small and large polystyrene sphere particles in water. It is shown that, based on the measurements of the time-resolved backscattered copolarized and cross-polarized components of the incident polarized light, either linearly or circularly polarized light can be used to effectively image an object that is deep inside a turbid medium composed of small particles, depending on the depolarization properties of the object itself. For large particles such as in tissue, fog, and clouds, the experimentally observed polarization memory effect on the backscattering temporal profiles suggests that a significant improvement in the image contrast can be achieved by use of circularly polarized light.     

Three-photon ionization of the potassium atom by linearly and circularly polarized light

The measurement and calculation results of the dependence of the three-photon ionization process of potassium atoms by linearly and circularly polarized light within the frequencies from 16300 to 16600 cm^-1 are presented. The experimental data do not confirm the predictions of perturbation theory on the existence of a window of nonlinear transparency for circularly polarized light.     

Micrometre double-quantum ionization of Rydberg hydrogen using linearly and circularly polarized light

The European Physical Journal D - We investigate the two-color two-photon K-shell ionization of neutral atoms based on the relativistic second-order perturbation theory and independent particle...     

Propagation of circularly polarized light in media with large-scale inhomogeneities

Small-angle multiple scattering of circularly polarized waves in disordered systems composed of large (larger than the light wavelength) spherical particles is discussed. The equation for Stokes’s fourth parameter V — the difference between the intensities of the left-and right-hand polarized light — is shown to have the form similar to that of the scalar transport equation for intensity I, the only difference being the presence of an additional “non-small-angle” term responsible for depolarization. In the case of small-angle scattering, depolarizing collisions are relatively rare and, in contrast to the scalar case, the problem contains an additional spatial scale, namely the depolarization depth. The polarization degree and helicity of the scattered light are calculated for the case of purely elastic scattering and in the presence of absorption in the medium. For strong absorption, depolarization is shown to follow the transition to the asymptotic regime of wave propagation. The features appearing in strong (non-Born) single scattering are also discussed. Zh. éksp. Teor. Fiz. 115, 769–790 (March 1999)     

双轴螺旋向性负材料中极化光波的左-右旋偏振耦合

研究了双轴螺旋向性负材料中极化光波的左 右旋偏振耦合效应.证明这种极化光的左-右偏振耦合效应导致在介质中传播的左右旋光具有频率移动效应.讨论了极化光左-右偏振耦合效应的起源（非局域极化效应）与它的若干应用, 如可控位置依赖频移. 关键词： 左-右偏振耦合 负材料 频移     

Visualization of scattering media upon backscattering of a linearly polarized nonmonochromatic light

The method of polarization visualization of multiply scattering macroinhomogeneous media, based on analysis of the spatial distributions of polarization characteristics of a linearly polarized radiation backscattered from a medium, is discussed. The effect of optical characteristics of the medium and the scattering geometry on the quality of the images obtained in the case of visualization of an absorbing heterogeneity immersed into a multiply scattering medium is considered. The comparative analysis of the quality of formed images was performed with the use of different polarization characteristics of the backscattered radiation as a visualization parameter. The theoretical interpretation of the obtained experimental results is given within the framework of the phenomenological approach based on the concept of the distribution of the effective optical paths of partial components of the scattered optical field. To calculate the probability density of the effective optical paths, the statistical simulation method was used.     

光强连续可调的圆偏振光衰减器

利用1/4波片及偏光棱镜,设计了光强连续可调的圆偏振光衰减器,通过该器件可获得偏振度高且光强连续可调的圆偏振光.该衰减器解决了632.8 nm多膜氦氖激光器出射光为非完全自然光且偏振面随时间做随机变化导致实验误差的问题,为偏光信息测试系统提供了相对稳定的激光光源.     

Bloch oscillations for circularly polarized light

All previous investigations on the Bloch oscillations of waves focus on scalar waves. Here we demonstrate, for the first time, the existence of Bloch oscillations of vector fields for circularly polarized light (CPL) propagating through a designed liquid crystal structure. To obtain the Wannier-Stark ladder of the CPL, we have designed a cholesteric liquid crystal structure with spatially varying pitch. The Bloch oscillations of the CPL have been observed in such a structure by exact numerical simulations. We have also shown that such a phenomenon can be easily detected in time-resolved reflection experiments.     

Optimization of focusing of linearly polarized light

We show that, by adding a π-phase shift to one-half of a linearly polarized beam, the roles of the transversal and longitudinal field components of the focused beam are interchanged, resulting in better focusing of the longitudinal component in the direction perpendicular to the phase jump line. For this component the scheme produces a spot with FWHM >15% smaller than a spot generated with either linearly or radially polarized light for any NA. The scheme has a similar advantage when applied to circularly polarized light, and it holds for both a plane wave and a realistic case of a Gaussian incident beam. This technique may find applications when using recording media responsive to the longitudinal field only, particularly in read/write for optical storage where the resolution in one transverse dimension is most important.     

All-optical magnetic recording with circularly polarized light

We experimentally demonstrate that the magnetization can be reversed in a reproducible manner by a single 40 femtosecond circularly polarized laser pulse, without any applied magnetic field. This optically induced ultrafast magnetization reversal previously believed impossible is the combined result of femtosecond laser heating of the magnetic system to just below the Curie point and circularly polarized light simultaneously acting as a magnetic field. The direction of this opto-magnetic switching is determined only by the helicity of light. This finding reveals an ultrafast and efficient pathway for writing magnetic bits at record-breaking speeds.     

Coherent effects in multiple scattering of linearly polarized light

Comparing the stochastic Monte Carlo technique with the iteration procedure for solving the Bethe-Salpeter equation in the framework of numerical simulation, the time correlation function and the interference component of the coherent backscattering of a linearly polarized light wave in a multiply scattering medium are calculated. The results of the simulation agree well with theoretical results obtained by generalizing the Milne solution, as well as with experimental data.     

Phase fluctuations and localization length in layered randomly inhomogeneous media

We consider the problem of the inclined incidence of a plane wave on the halfspace of a randomly inhomogeneous layered medium without absorption. The probability distribution of the reflection coefficient phase with respect to the incidence angle is calculated. With the help of this distribution we analyse the quantities connected with localisation effects—the length localization and moments of the intensity inside the medium.     

Phase fluctuations and localization length in layered randomly inhomogeneous media

Abstract

We consider the problem of the inclined incidence of a plane wave on the halfspace of a randomly inhomogeneous layered medium without absorption. The probability distribution of the reflection coefficient phase with respect to the incidence angle is calculated. With the help of this distribution we analyse the quantities connected with localisation effects—the length localization and moments of the intensity inside the medium.     

Photomagnetization of polydomain magnetic insulators by circularly polarized light

A new effect of magnetization of magnetic insulators due to light absorption by magnetic ions is proposed. The estimates for an yttrium ion garnet crystal are made.     

Filtering of light in randomly layered media

We use the analogy with the transmission properties of the random dimer system to model a system of random monolayers and study the transmission of light for different disorder strengths. We show the existence of unity resonant transmission peaks, corresponding to extended modes, controlled by the thickness of the layers. These peaks become narrower if we increase the refractive index of the impurity layers or their number. The very high resolution of the transmitted light leads us to discuss the possibility of making high quality light filtering devices based on such a layered system.