Cooperation of traveling and quasi-cutoff waves in a cyclotron-resonance maser

A new version of a cyclotron-resonance maser is studied theoretically and experimentally. Here, a spatially periodic helical electron beam couples traveling (autoresonance) and quasi-cutoff (gyrotron) waves of the same frequency, interacting with them at different cyclotron harmonics. The theory and early experimental results show that this maser can effectively generate a traveling wave with low quasi-cutoff wave excitation losses using a very simple feedback system.     

Pairs of opposite decaying evanescent waves in random media and tunneling radiative transfer

A tunneling mechanism of radiative transfer through a dielectric random medium is revealed applying technique of Dyson and Bethe-Salpeter equations for electromagnetic wave multiple scattering by medium inhomogeneities (scatterers) with near fields effects in scattered fields. The mechanism consists in existing inside of a random inhomogeneity a pair of virtually opposite decaying evanescent waves whose interference results in energy flux.     

Quantum modulation of an electron beam in the field of opposite electromagnetic waves

The quantum modulation of an electron beam in the field of opposite electromagnetic waves, at a frequency equal to the difference of the wave frequencies, and its harmonics, is obtained. The depth of the modulation becomes of order one at relatively small intensities of the laser fields (including a real spreading of the beam). In the case of equal frequencies of the waves (when the Kapitza-Dirac effect occurs particles form a beam. An experiment for obtaining a modulated beam of particles at the frequencies of the laser radiation, and its harmonics, as well as for bunching of particles in the field of a standing wave is suggested.     

Criticality in lasers and masers

A critical length for laser self Q-switching and a self oscillation condition for an astrophysical maser are derived by analogy with neutron criticality, with back-scattering of radiation as the coupling process.     

Effective dichroism in forward scattering by inhomogeneous birefringent medium

The Mueller matrix model for inhomogeneous medium characterized by simultaneous linear and circular birefringence for single scattering in the forward direction is derived. We find that the presence of inhomogeneity results in the occurrence of new polarization effects. In particular, forward scattering by inhomogeneous birefringent medium exhibits linear and circular dichroism. We show that in the case of weak depolarization (when Cloude's entropy is less than 0.5), the initial parameters for linear and circular birefringence can be obtained from deterministic Mueller matrix associated with the largest eigenvalue of Cloude's coherency matrix. Sample calculations are given for quartz.     

Effective tortuosity and different acoustic waves in porous media

Summary A simple method has been suggested to estimate the acoustic characteristics of porous structure from a hybrid model—a hybridisation of Biot's phenomenological model and the microscopic multiple-scattering theory which introduces the idea of an effective tortuosity. Without using any adjustable parameter this model may be used to provide rough estimates of the tortuosity, the fast, the shear and the slow sound speeds. The predictions are compared with observation on water-saturated glass bead samples. The author of this paper has agreed to not receive the proofs for correction.     

Modulational instability,rogue waves,and envelope solitons in opposite polarity dusty plasmas

Dust-acoustic (DA) waves (DAWs) and their modulational instability (MI) have been investigated theoretically in a plasma system consisting of inertial opposite polarity (positively and negatively) warm adiabatic charged dust grains as well as inertialess non-extensive $q?$distributed electrons and non-thermal ions. A nonlinear Schrödinger equation (NLSE) is derived by using the reductive perturbation method. It has been observed from the analysis of NLSE that the modulationally stable solitary DAWs give rise to the existence of dark envelope solitons, and that the modulationally unstable solitary DAWs give rise to the existence of bright envelope solitons or rogue structures. It is also observed for the fast mode of DAWs that the basic features (viz. stability of the DAWs, MI, growth rate, amplitude, and width of the DA rogue waves, etc.) are significantly modified by the related plasma parameters (viz. dust masses, dust charge state, non-extensive parameter q, and non-thermal parameter α). The results of our present investigation might be useful for understanding different nonlinear electrostatic phenomena in both space (viz. ionosphere and mesosphere) and laboratory plasmas (viz. high intensity laser irradiation and hot cathode discharge).     

Rogue waves for Kadomstev-Petviashvili solutions in a warm dusty plasma with opposite polarity

Kadomstev-Petviashvili (KP) equation is derived using reductive perturbation method. This equation transformed into a nonlinear Schrödinger equation (NLS) by using appropriate variable transformations. When the carrier wave frequency is much smaller than the dust plasma frequency, the DA waves generating modulated wave packets in the form of rogue waves. The dependence of rogue wave profile on system plasma parameters investigated numerically. The parameters in this model are within the ranges corresponding to upper mesosphere, cometary tails and Jupiter’s magnetosphere.     

Competition and coupling between forward and backward waves in optically-pumped linear-cavity fir lasers

We study theoretically the gain for a linear-cavity (Fabry-Perot) FIR laser pumped by a travelling-wave infrared beam. Arbitrary field intensities and pressure and Doppler broadenings are considered. The simultaneous presence inside the laser cavity of the forward and backward generated waves produces strong competition and coupling effects between these waves which are interpreted in terms of Lamb-dip and multiphoton processes. These effects determine the main differences in the amplifying behaviour between the bi-directional (linear) and uni-directional (ring) laser configurations.     

Effect of homogeneous broadening on the generation of forward and backward waves in induced superradiance

It is shown that homogeneous broadening in induced superradiance weakly affects the cooperative exchange between forward and backward waves in a sample. At the same time, homogeneous broadening increases the delay time and attenuates the superradiance pulse intensity. As a result, it may change the regime of predominance of the transmitted or reflected wave.     

A simple model of forward ionization waves related with acoustic phenomena

Derivation of a very simple theory of forward waves, based on the conception that their phase and group velocities are determined mainly by acoustic processes.Main results of this work have been presented on the 5th Conference of Czechoslovak Physicists, held in Koice, 29. 8.–1. 9. 1977.     

Effective solution for Rayleigh-type waves in a randomly inhomogeneous medium

This paper is concerned with the effective solution for Rayleigh-type waves in a randomly inhomogeneous layer overlying a homogeneous half-space. The considerations are confined to the correlation theory. The method is based on the idea of a fundamental matrix for the system of differential equations. By using the Bourret approximation the system of coupled two second-order integro-differential equations for the average displacements is obtained. This system is solved by Laplace transform. By using boundary and continuity conditions the particular solution is obtained.     

经典三阶驻波、短峰波的有效匹配解

发现经典非线性三阶驻波、短峰波解并不满足其所必须的波幅方程,这势必要影响与这些经典理论密切相关的现代短峰波理论的发展.基于此,提出了一套消除这种解与方程不相匹配的理论判据,从而可充分保证最终所得之解的内在和谐性和正确性. 关键词： 匹配解 理论判据 驻波 短峰波