Nonresonant Parametric Decay of a Finite Extent Lower Hybrid Wave

The decay of lower hybrid waves into nonresonant quasimodes inside the lower hybrid resonance cone is observed. Sideband frequency shifts of up to 30 percent from the pump frequency occur. The low-frequency mode is identified as a nonresonant quasi-mode satisfying the approximate conditions ?/k? ? ?e. The sideband wave-number and the sideband and quasi-mode growth rates were measured. The transition between ion-acoustic mode and quasi-mode decay spectra is observed as plasma density or pump frequency is varied.     

Nonresonant and Resonant Nonlinear Absorption of CdSe-Based Nanoplatelets

We present a comprehensive understanding of the nonlinear absorption characteristics of CdSe-based nanoplatelets(NPLs) synthesized by the solution-phase method and the colloidal atomic layer deposition approach through Z-scan techniques at 532 nm with picosecond pulses. The CdSe NPLs exhibit strong two-photon induced free carrier absorption(effective three-photon absorption) upon the nonresonant excitation, resulting in a remarkable optical limiting behavior with the limiting threshold of approximately 75 GW/cm~2. A nonlinear optical switching from saturable absorption(SA) to reverse saturable absorption(RSA) with increasing the laser intensity is observed when coating CdSe NPLs with a monolayer of CdS shell to realize the resonant absorption. The SA behavior originates from the ground state bleaching and the RSA behavior is attributed to the free carrier absorption.These findings explicitly demonstrate the potential applications of CdSe-based NPLs in nonlinear optoelectronics such as optical limiting devices, optical pulse compressors and optical switching devices.     

Parametric Excitation of Electromagnetic Fields by two Pump Waves

A collisionless plasma in the presence of two monochromatic electric fields is considered. By means of a kinetic analysis, a dispersion relation that governs the excitation of transverse electromagnetic fluctuations is derived and analysed.     

Anomalous Absorption of Radio Waves by Small-Scale Magnetic-Field-Aligned Irregularities

We study the anomalous absorption of radio waves by small-scale magnetic-field-aligned artificial irregularities taking into account the effect of such irregularities on the propagation of the excited Z -mode. It is shown that this process becomes significant if the transverse size of field-aligned irregularities is of the order of 0.1c/ω or greater, where ω is the radio wave frequency and c is the speed of light in vacuum.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 3, pp. 181–197, March 2005.     

Parametric Instabilities of Waves in Magnetized Plasmas

Results from kinetic theory are reformulated in order to generalize previous equations for wave-wave interactions in magnetized plasmas.     

Parametric Decay of Electron Electrostatic Waves Pumped by an Electromagnetic Wave

In a computer simulation study, we have observed the parametric decay of an electromagnetic wave propagating parallel to the DC magnetic field into two electron electrostatic waves. We have identified the mechanism as three-wave parametric interaction. The growth constants of the decay waves have been measured. After saturation, the decay waves are observed to trap electrons. Consequently, the velocity distribution function develops a high velocity tail. The details of these processes are discussed. We have found that the kinetic energy of the total assembly of electrons will increase by about a factor of four.     

Absorption/Scattering of Scalar Waves by Dilatonic Black Hole

We investigate the scattering and absorption cross sections of scalar waves by Garfinkle-Horowitz-Strominger (GHS) black hole spacetime with partial wave method. We find that the total absorption cross section oscillates around the geometric optical value, and the scattering angle width becomes narrower and the damping oscillation pattern becomes more complex as l increases. With fixed frequency ω, the main glory peak value becomes higher and the glory width becomes wider as the magnetic parameter a increases.     

On Nonlinear Resonant Absorption of Surface Waves

We consider the resonant absorption of surface waves in a cold electron plasma by taking into account the nonlinear change in the electron density profile which is caused by the wave pressure in the transition layer. Equations, which describe the time evolution of the amplitudes of the electric fields of the surface waves, are obtained and solved. It is shown that the time-behaviour of the surface waves can be significantly different from that obtained from linear theory, and nonlinear effects can thus change the rate of absorption of the surface wave energy and can also stabilize linear surface wave instabilities.     

Parametric Representation of 3D Grain Ensembles in Polycrystalline Microstructures

As a straightforward generalization of the well-known Voronoi construction, Laguerre tessellations have long found application in the modelling, analysis and simulation of polycrystalline microstructures. The application of Laguerre tessellations to real (as opposed to computed) microstructures—such as those obtained by modern 3D characterization techniques like X-ray microtomography or focused-ion-beam serial sectioning—is hindered by the mathematical difficulty of determining the correct seed location and weighting factor for each of the grains in the measured volume. In this paper, we propose an alternative to the Laguerre approach, representing grain ensembles with convex cells parametrized by orthogonal regression with respect to 3D image data. Applying our algorithm to artificial microstructures and to microtomographic data sets of an Al-5 wt% Cu alloy, we demonstrate that the new approach represents statistical features of the underlying data—like distributions of grain sizes and coordination numbers—as well as or better than a recently introduced approximation method based on the Laguerre tessellation; furthermore, our method reproduces the local arrangement of grains (i.e., grain shapes and connectivities) much more accurately. The additional computational cost associated with orthogonal regression is marginal.     

激光长程吸收光谱法测量高分辨率大气吸收光谱

用脉冲可调谐光参量振荡器作光源 ,使用光程长达 1km的 8m长吸收池 ,采用分时复用的单探测器探测方法 ,组成测量系统 ,测量了一系列高分辨率的模拟和实际大气的吸收光谱。系统的灵敏度为 0 .5× 10 - 6cm- 1 ,分辨率为 0 .0 2cm- 1 。 1.315 μm附近实际大气的吸收光谱与HITRAN96模拟结果比较 ,强线符合得很好。水汽光谱的大多数强线的分子线强度相对误差在 10 %以下。     

On a Strong Effect of Nonresonant Three-Wave Interactions on the Saturation of Low-Threshold Parametric Decay Instability

JETP Letters - It has been shown that the nonresonant three-wave interaction between daughter waves trapped in the plasma, which excites strongly damped induced oscillations, strongly affects the...     

长光程吸收光谱空气质量监测方法问题分析

长光程吸收光谱空气质量监测是一种比较成熟的方法，但其在测定的准确性、长期工作的稳定性，数据检测等方面存在不少问题。对该方法的原理、仪器系统组成、运作环境等进行了介绍，论述了产生问题的原因。针对太阳散射光、吸收系数、系统光学部件和气候条件等诸多因素的影响进行了分析评述。     

Polarization Phenomena in Transparency and Absorption Effects Induced by the Field of Unidirectional Waves

Physical processes that form the spectra of saturated absorption and magnetic scanning resonances on an atomic transition with level momentum J = 1 in the field of unidirectional waves of arbitrary intensity under variation in their polarization directions are investigated by numerical simulation and analytically. It is shown that anomalies in nonlinear resonance spectra are determined by the polarization of the waves and the degree of openness of the atomic transition, while anomalies in the experimentally observed magnetic scanning spectra are attributed to the magnetic coherence induced by the fields directly on the levels of the lower state, rather than to its transfer from the excited states, as was assumed earlier.     

Nonresonant and stochastic heating of ions by low-frequency wave

The present paper addresses the nonresonant and stochastic heating of minor ions by a low-frequency Alfvén wave in the solar wind. A new and whole physical mechanism that enables the heating of ions by a low-frequency parallel propagating wave with finite amplitude in a low beta plasma. The heating process has two stages: First, ions are picked up via low-frequency wave–ion nonresonant interaction and the ion energy gain depends on the ratio of the wave electric-field energy to background magnetic-field energy. Second, when the velocity approaches the threshold value, the stochastic heating is prominent. The stochastic heating of ions sustains until the average parallel speed is close to the wave velocity.