Coherent backscattering of polarized light from a turbid medium

Approximate analytical expressions for the intensities of the polarized components of light reflected from a disordered medium with large discrete particles (larger than the wavelength) have been derived with the use of the method of decoupling of the vector transfer equation that is based on separate treatment of basic and additional polarization modes. The results obtained provide the relation between the peak shape in the angular distribution of the backscattered radiation with a given polarization and the optical characteristics of the medium and are in good agreement with experimental data and numerical calculations.     

Modulation of electromagnetic waves by time-dependent magnetic fields in a ferrite

The modulation of phase and amplitude of an electromagnetic wave in a ferrite by a longitudinal, time-dependent (sinusoidally modulated) magnetic field has been investigated. In the case of an infinite medium, an analytical expression for the amplitude envelope of the wave is obtained and it is found that the envelope differs appreciably from the sinusoidal form. In the case of a ferrite slab, the amplitude of the transmitted and the reflected components of the magnetic vector have been evaluated by an expansion method. Numerical calculations indicate, as expected, that for a uniform plane wave incident on a ferrite sheet of finite thickness, the transmitted beam is strongly amplitude modulated.     

Transformation and shift of a Gaussian light beam upon reflection from a resonant medium

The specific features of the transformation and shift of a Gaussian beam reflected from a resonant absorbing medium are analyzed numerically. The study is based on the expansion of the field of the incident Gaussian beam into plane-wave components by using the Fourier integral transform. The calculations are performed for a frequency range covering the resonance region. The conditions for the splitting of the profile of the reflected beam and for its negative shift are established.     

Experimental verification of the technique for calculating light scattering in turbid media and determination of the single-scattering albedo based on the spectroscopy of elastically reflected electrons

The equations of light transfer in a turbid medium and transfer equations for electrons undergoing only elastic collisions in a solid body are shown to be equivalent. The angular distributions of elastically reflected electrons were calculated using the DISORT and MDOM optical codes. The calculation data are compared with the results of experimental measurements for the angular distributions of elastically reflected electrons and with calculations according to the Monte-Carlo method. Optical codes are shown to be highly efficient in calculating the angular distributions of electrons elastically reflected from multilayer media.     

Theoretical Investigation of Tunable Goos-Hänchen Shifts in a Four-Level Quantum System

Goos-Hänchen (GH) shifts in the reflected and transmitted light have been discussed in a cavity with four-level quantum system. It is realized that the refraction index of intracavity medium can be negative by manipulating the external coherent laser fields. For the negative refraction index of intracavity medium, the GH shifts of reflected and transmitted light beams have been analyzed in a parametric condition. It is found that due to modulation of laser signals and relative phase between applied fields, large and tunable GH shifts in reflected and transmitted light beams can be obtained.     

Reflection of surface acoustic waves in the bulk of a hexagonal single crystal

It has been shown that surface acoustic waves in some hexagonal crystals can include not only the waves outgoing from the surface into the bulk of the crystal but also the reflected waves, i.e., those coming from the bulk of an infinite single crystal. The outgoing and reflected waves decay exponentially with the distance from the surface. It has been found that the reflected wave can exist if the velocity of its propagation is below the critical value, which does not exist for some crystals. The numerical calculations have shown in what real hexagonal crystals the reflected wave can exist. The values of the critical velocity have been found for a number of hexagonal crystals.     

Calculation of Transfer Functions of Multilayer Biotissues in the Problems of Correction of Their Fluorescence Spectra

A method for rapid calculation of a flux of stimulated fluorescence of a multilayer optically dense medium with inhomogeneous distribution of the fluorophore has been developed. The light field in the medium at the excitation wavelength of fluorescence is represented by a superposition of incident collimated, incident diffuse, and reflected diffuse fluxes. A two-stream approximation is used to describe the light field in the medium at the wavelength of emission of the fluorescence. Fluxes in adjacent elementary layers of the medium and on its surface are connected by simple matrix operators that are obtained using a combination of engineering approaches of radiation-transfer theory and single-scattering approximation. The calculations of fluorescence fluxes of a four-layer biotissue that are excited and recorded at 400–800 nm are compared with their Monte Carlo simulation with a discrepancy of 1%. The effect of the propagation medium on the fluorescence spectra of 5-ALA-induced protoporphyrin IX that are recorded from human skin was studied, and a technique for their correction that is based on measurements and quantitative analysis of the diffuse reflectance spectrum of skin was proposed.     

吸收媒质界面上反射束的非镜像纵向位移

导出可用于计算来自吸收媒的反射束之ｓ偏振及ｐ偏振的纵向焦位移值的两个表达式。计算表明，Ｆｐ是正值，即ｐ波沿反射方向漂移；Ｆｓ是负值，因而ｓ波沿相反方向漂移。若令消光系数为零，这两个表达式简化成Ｃｈａｎ和Ｔａｍｉｒ给出的但仅适用非吸收媒质的公式。     

MEASUREMENT OF L-SHELL IONIZATION CROSS SECTIONS FOR NIOBIUM BY ELECTRON IMPACT

L-shell ionization cross sections of Nb by electron impact in the energy range from 3 to 40 keV have been determined with a Si(Li) X-ray detector. Influence of reflected electrons from backing on the measurement was corrected using an electron transport model. The experimental results are compared with theoretical calculations of Gryzinski and McGuire.     

Energy and charge distribution of helium atoms reflected from a Cu surface under grazing incidence

The energy and charge distributions of helium ions and atoms reflected from a Cu surface at grazing incidence have been measured at the energies 250 and 300 keV. The dependence of the relative number of helium atoms in the scattered beam on the scattering angle at incidence angles less than 2° and scattered particle energies below 150 keV has been discovered. It is shown that, for a theoretical estimation of the charge fractions of particles reflected from the target surface, charge-exchange cross sections used in calculations must be corrected when solids are considered instead of gases.     

二极管侧泵浦板条固体激光器的热效应研究

 用有限差分法对二极管侧泵浦板条激光介质的温度分布作了数值计算。在此基础上, 对不同条件下二极管侧泵浦激光器的最佳冷却方案进行了研究。用峰值功率为100W, 工作频率为100Hz的二极管泵浦Nd:YAG板条作了实验研究, 所得结果与计算符合较好。     

The parametric Doppler effect upon oblique incidence of probe radiation

Transformation of frequency and intensity of probe radiation obliquely incident on a moving inhomogeneity induced by an intense laser radiation in a nonlinear medium is analyzed. The dependences of frequency and intensity of radiation reflected from the inhomogeneity have been found for a variant of frequency dispersion corresponding to collision-free plasma. These dependences possess singularities under conditions corresponding to the Vavilov-Cherenkov effect. The initially weak noise components of probe radiation increase in the reflected radiation up to a considerable value.     

On the photoelectron spectrum of sulphur trioxide

He(I), He(II) and variable temperature Ne(I) photoelectron spectra of sulphur trioxide are reported. All six of the expected ionic states have been detected and assigned; the assignment differs from a previous one. Ab initio calculations in a medium basis set have been carried out and spectral intensities have been calculated; agreement between the calculations and the spectra is good. The calculations show a substantial S(3d) character in the S-O bond, and the spectra are consistent with this.     

Theoretics of remote acoustic monitoring of the level and density of fluid contacting media at the interface

We present a method for monitoring the physical parameters of a medium, based on processing of an acoustic signal reflected from the studied medium. The method makes it possible to rapidly and simultaneously measure the level and density of the reflecting medium owing to acoustic sounding with pulses of different shape. We have obtained the analytic dependences relating the controlled parameters to the phase and amplitude spectra components of the reflected acoustic signal.     

A dynamic phase-conjugate mirror based on CdF<Subscript>2</Subscript> crystals with bistable centers

A four-wave phase-conjugate mirror on reflection gratings recorded in a CdF₂ crystal with bistable centers has been studied experimentally. The mirror reflectivity and speed have been measured, and the coefficient of third-order nonlinearity of this medium has been estimated. The quality of the wave reflected from the phase-conjugate mirror has been investigated in model experiments.     

Intensities of helium Stark lines in the region of levels anticrossing between n = 6 and n = 7

Studies of intensities of Stark lines of atomic He have been performed. The applied fields were high enough that shifts of the upper levels of the observed transitions became larger than the separation distance between levels with different principal quantum numbers. Overlapping of structures belonging to neighboring principal quantum numbers leads to levels anticrossing effects, what is reflected in variation of intensities of the observed spectral lines. Using the density matrix theory, calculations of the line intensities have been performed. By matching the superpositions of the excited states in the theoretical calculations we can follow the results of observation. Computer simulations have been performed for the observed levels anticrossing region between n = 6 and n = 7 in the second triplet series (2³P–n³Q, Q = S, P, D, ...).     

The wave flow effect on a plane boundary between vacuum and an optical medium with a quasi-zero refractive index

A boundary problem in which a plane electromagnetic wave is reflected and refracted at a plane boundary of a semi-infinite optical medium with a quasi-zero refractive index has been solved. Such a medium has a random refractive index taking values in an interval from zero to some finite value less than unity. It means that the concept of a sharp interface between two media loses its meaning, the boundary of the medium becomes inhomogeneous, and laws of reflection and refraction of light become non-Fresnelian. Formulas for non-Fresnelian amplitudes of reflection and refraction have been derived. It is shown that a surface wave arises near the boundary of a medium with a quasi-zero refractive index. The wave propagates both on the inside and outside of the boundary.     

Features of the scattering of protons and relativistic electrons intersecting a thin planar target at a small angle to its surface

The processes of scattering of protons and relativistic electrons incident on a planar target at a small angle to its surface have been simulated by the Monte Carlo method. The spatial and energy distributions of the beams of particles both passed through the target and reflected from it have been calculated. The dependence of the characteristics of beams on the initial energy and direction of injection of particles, as well as on the material and thickness of the target, has been considered. The transmission, reflection, and absorption coefficients for electrons in the target have been calculated. The initial energy in the calculations is varied in the range of 7–100 MeV and the angle between the trajectory of particles and the surface of the target is in the range of 1°–45°. The thickness of the target varies from 0.2 to 3 mm. Aluminum, iron, and copper targets have been considered. It has been shown that the intersection of targets at small angles not only increases the transverse dimensions of a beam, but also changes the direction of its motion. The results of the reported calculations of the scattering of relativistic electrons intersecting a foil at small angles to its surface are in qualitative agreement with experimental data.     

Quantum theory of laser cooling: Statistical description of the process dynamics

A dynamic theory of coherent X-ray radiation generated in a periodic layered medium by a relativistic electron multiply scattered by target atoms has been developed. The expressions describing the spectral–angular characteristics of parametric X-ray radiation and diffracted transition radiation are derived. Numerical calculations based on the derived expressions have been performed.     

Ponderomotive action of light in the problem of multiple scattering of light in a randomly inhomogeneous medium

The time correlation function of light reflected diffusely from a semi-infinite randomly inhomogeneous medium is calculated with allowance for the acceleration of the scatterers in the field of the laser beam incident on the medium. An analytical expression is found for the characteristic coherence time due to the ponderomotive action of light. It is shown that even with laser radiation power densities of the order of 1–10 W laser-acceleration effects substantially alter the character of the time autocorrelation function of the scattered light and must be taken into account in theoretical calculations. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 611–615 (10 May 1998)