Transformation of electromagnetic radiation at moving inhomogeneities of a medium

The possibility of a significant up-conversion of the electromagnetic-radiation frequency due to its Doppler shift by ultrarelativistic nonlinear-medium inhomogeneities induced by high-intensity counterpropagating radiation pulses is analyzed. It is shown that the efficiency of parametric redistribution increases resonantly as the velocity of the inhomogeneity approaches the phase velocity of the high-frequency radiation.     

Subluminal and superluminal parametric doppler effects in the case of light reflection from a moving smooth medium inhomogeneity

The reflection of test radiation from a smooth inhomogeneity of medium characteristics propagating with a subluminal or superluminal velocity is analyzed. The equations describing the propagation of the forward- and counter-propagating waves in such an inhomogeneous medium are derived. Quasi-phase conjugation is demonstrated in the case of superluminal inhomogeneities. The Bragg resonance conditions are formulated and the conditions for increasing the reflection coefficient of radiation from an inhomogeneity are discussed.     

Transformation of radiation upon its interaction with overtaking inhomogeneity in a medium with dispersion

The parametric Doppler effect is analyzed and simulated numerically in the case in which a wave or a pulse of optical radiation interacts with an inhomogeneity overtaking it in a medium with frequency dispersion. It is shown that, as the velocity of the inhomogeneity motion approaches the speed of light in vacuum, the frequency of the transformed radiation increases unboundedly but the efficiency of the transform decreases up to the zero value.     

Superluminal parametric Doppler effect in insulators and in an electron-positron vacuum

It has been shown that counterpropagating electromagnetic waves with different frequencies generate two lattices in a cubically nonlinear medium, one of which moves at a superluminal velocity. When weak radiation reflects from the superluminal lattice, the wavefront is quasi-conjugated with distortions owing to the Doppler frequency shift. These effects occur both in insulators with fast nonlinearity and in an electron-positron vacuum.     

Forward light reflection from a moving inhomogeneity

The reflection of monochromatic and quasi-monochromatic pulsed light incident on a moving inhomogeneity in the optical characteristics of a medium having plasma-type dispersion has been analyzed. The velocity V of the inhomogeneity, induced in the medium by an intense laser pulse, has been changed by varying its carrier frequency. It has been shown that the usual back-reflection mode, when the reflected radiation pulse moves in the direction opposite the direction of incident radiation, is implemented only if the velocity V is less than the critical value V _min, which depends on the carrier frequency of the incident radiation pulse. It has been found that reflected radiation moves in the same direction as the incident radiation in a certain range of the velocity V _min < V < V _max (forward reflection). In this case, the reflected radiation pulse begins to lag behind a fast-moving inhomogeneity. When V _max < V < c, where c is the speed of light in vacuum, the group velocity of the incident radiation pulse is less than the speed of inhomogeneity, and there is no reflection. Analytical treatment is supported by numerical simulation.     

Optical Detection of Motion of an Object with a Refractive Index Coinciding with the Refractive Index of the Surroundings

Estimates of characteristics of light reflection from an object moving with a constant velocity in a medium whose refractive index coincides with the refractive index of the object are presented. The back-reflected radiation has a frequency shift owing to the Doppler effect, and the reflectivity turns out to be a quantity of the first order in the ratio of the velocity of motion to the velocity of light in a vacuum. If the velocity of motion of the surroundings near the object boundary varies in a boundary layer of a width that appreciably exceeds the wavelength, the reflectivity falls off exponentially with the ratio of these quantities. The estimates performed testify that the possibility of observing the effect of relativistic reflection under consideration is quite realistic.     

The parametric Doppler effect upon reflection of light from a moving smooth inhomogeneity of a medium

The reflection of probe radiation from a smooth inhomogeneity of characteristics of a medium that propagates with a relativistic velocity is analyzed. Equations that describe the propagation of forward and backward waves in an inhomogeneous medium are derived, conditions of occurrence of a Bragg resonance are formulated, and conditions for increasing the coefficient of reflection from the inhomogeneity are discussed.     

Interaction of pulsed laser beams in quadratic nonlinear media

A theory of three-wave cascade interaction of pulsed laser beams in quadratic nonlinear media is developed with regard to diffraction and dispersion. The space-time trajectories of signal motion in a medium with an inhomogeneity induced by high-power low-frequency pumping are analyzed. It is shown that total signal reflection from a moving localized inhomogeneity can be implemented. This reflection is accompanied by a change in the frequency, velocity, and propagation direction of the signal wave.     

获取超短波长电磁辐射的新途径

在系统研究运动电子对迎面而来的圆偏振激光脉冲的汤姆逊散射的基础上，讨论了获取超短波长电磁辐射的两种新方案。其一是利用超强圆偏振激光在具有特定速度的电子的非线性散射所伴随的谐波频率上称，其二是利用激光在相对论电子反向散射所伴随的多普勒频移。     

Parametric Doppler effect in the case of oblique incidence in a medium with a plasma dispersion law

The parametric Doppler effect that occurs upon reflection of a plane monochromatic wave obliquely incident on an inhomogeneity of the refractive index moving in a medium with a frequency dispersion (homogeneous wave regimes) is analyzed. For a plasma-type frequency dispersion, the dependences of the frequency and angle of reflection on the frequency of the incident wave and on the angle of incidence are found.     

The doppler frequency shift caused by the inhomogeneities of a medium induced by pulses of intense laser radiation

Self-reflection of pulses of intense laser radiation from an inhomogeneity induced by them in a medium with fast optical nonlinearity is analyzed. The reflected radiation is characterized by a considerable Doppler shift and by a signal magnitude that is sufficient for experimental detection.     

The parametric Doppler effect in a medium with Lorentz dispersion

The frequency conversion under the parametric Doppler effect, which occurs when weak probe radiation reflects off from a refractive index inhomogeneity induced in a nonlinear medium by intense pumping, has been analyzed. Under these conditions, the frequency dispersion of the medium is assumed to correspond to the single Lorentz oscillator model. It is shown that the presence of resonance and a spectral range forbidden for propagation may lead to a complex Doppler effect, where the incident radiation is single-frequency but the reflected radiation consists of two or three monochromatic waves, one of which has a phaseconjugated wavefront.     

On scattering of electromagnetic radiation by inhomogeneities of the velocity of motion of the medium

Analysis of the scattering of a plane monochromatic electromagnetic wave by an inhomogeneity of the velocity of motion of the medium is carried out. The inhomogeneity corresponds to the rotation of a finite portion of the medium with a constant angular velocity under the conditions of spatial homogeneity of the permittivity and the permeability. The case of oblique incidence of the wave is studied. The scattering cross sections for an inhomogeneity having the shape of a cylinder or a sphere of different dimensions are found for different angles of incidence of radiation.     

Relativistic scattering of electromagnetic radiation by inhomogeneities of the velocity of motion of the medium

Analysis of the relativistic scattering of electromagnetic radiation by inhomogeneities of the velocity of the motion of a medium is carried out. The characteristics of the scattering of a plane monochromatic wave by a rotating dielectric cylinder surrounded by an immobile medium with a refractive index the same as that of the cylinder are calculated. The differential scattering cross section is found. It is shown that the rotation of particles with actual parameters may yield a significant contribution to the scattering, of the same order of magnitude or larger than the contribution made by Rayleigh and Raman scattering.     

The parametric doppler effect upon oblique radiation incidence in quartz glass

Frequency and reflection angle of probe radiation from a refractive-index inhomogeneity induced by an intense pumping pulse in quartz glass and moving with a relativistic velocity are calculated. Conditions under which the normal component of the wave vector of the reflected wave is directed to the opposite or to the same direction as the same component for the incident wave are determined. Comparison with the case of radiation reflection from a relativistic mirror in vacuum is performed. Conditions of the appearance of the Vavilov-Cherenkov radiation from a relativistic refractive-index inhomogeneity induced in the medium by an intense laser pulse are discussed.     

Radiation reflection from inhomogeneities moving in a medium with a plasma dispersion law

The dependence of the complex frequency of radiation reflected from an inhomogeneity moving in a medium on the frequency of the incident radiation is found for inhomogeneous wave regimes. Explicit expressions for the plasma dispersion law of the medium are presented. The complex Doppler effect, where one (real) frequency of the incident radiation corresponds to two complex frequencies of the reflected radiation, is demonstrated.     

Lateral shift and tunneling of optical beam reflected from gradient-induced inhomogeneity

Two effects have been analytically and numerically studied: Goos-Hänchen shift, which is acquired by an optical beam reflected from a gradient inhomogeneity, and tunneling of radiation through a narrow induced inhomogeneity. A possibility of increasing the lateral beam shift in comparison with total internal reflection from a homogeneous medium is revealed. The dependence of the tunneling coefficient on the inhomogeneity parameters is determined and the critical inhomogeneity width at which the tunneling effect arises is found.     

低环径比托卡马克堆中的α粒子输运

基于当前等离子体物理，本文初步讨论了低环径比托卡马克堆中等离子体的特征。在自洽的低环径比堆芯参数下，计算了α粒子约束和损失，以及不同环径比对它们的影响。     

Transformation of optical radiation by fast-moving smooth inhomogeneities of a medium

For the problem of the reflection and transmission of monochromatic radiation by a moving smooth inhomogeneity of parameters of a motionless transparent medium, transport equations are derived and an approximate solution to these equations is obtained for the case of weak reflection. Estimates of the effects for quartz in the transparency region are given.     

The parametric Doppler effect in quartz glass

Transformation of frequency is analyzed under the parametric Doppler effect in quartz glass in the “optic collider” scheme. In this scheme, intense laser radiation induces moving inhomogeneities of the refractive index in the glass and the probe radiation undergoes the Doppler frequency shift when being reflected from them. The possibilities of transforming the frequency both within the main transparent region and from the main transparent region to the low- and high-frequency regions separated from the main region by absorption peaks in the infrared and ultraviolet spectral ranges are demonstrated.