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.     

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.     

Threshold Fields of Parametric Instabilities

The threshold electric fields of parametric decay instabilities in a magnetized plasma have been derived. Consideration is given to a unified presentation of a number of basic processes of particular interest.     

非简并光学参变振荡器的不稳定性研究

通过求得非简并光学参变振荡器的稳态解及特征值,研究了在共振与失谐两种情况下该系统的不稳定性.结果表明:共振时系统总是处于稳定状态,而有失谐时系统存在不稳定性.并通过数值模拟绘出共振情况下特征值随驱动场强度的变化曲线,及失谐时三个模量的输出信号随时间的变化情况.     

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.     

光纤偏振效应导致脉冲展宽的解析模型

在10Gb／s,尤其是40Gb／s以上高速光纤通信系统中,光纤的偏振特性已成为限制系统传输距离的主要因素之一。光纤的偏振效应主要包括偏振模色散和偏振依赖损耗。而脉冲均方根展宽是判断信号传输性能的一个主要物理量。本文讨论了光纤线路偏振模色散与偏振相关损耗的相互作用及对信号脉宽的影响。给出了线路偏振模色散矢量和偏振相关损耗矢量之间的关系式,并基于严格的数学方法,导出了在光纤偏振模色散和偏振相关损耗共同作用下的信号均方根脉宽变化的解析形式,同时考虑了光纤色散,啁啾等。该模型可用于分析高阶偏振模色散和偏振相关损耗,任意线性光纤通信系统脉冲展宽分析。     

多普勒展宽和多普勒频移在光谱分析中的应用

分析了多普勒展宽和多普勒频移区别，讨论了高斯拟合和弦积分线形分布的差异。利用多道光学分析仪（OSMA）测量HT-6M托卡马克限制器前Hα线形分布，通过高斯拟合由多普勒展宽和多普勒频移分别得出等离子温度和粒子入射速度。     

Theory of Parametric Instabilities and Harmonic Generation in Tonks-Dattner Resonances

Onedimensional fluid theory of Tonks-Dattner resonances in inhomogeneous, bounded plasmas is extended to stronger exciting electric fields. The relation of parametric instabilities and harmonic generation with Tonks-Dattner resonances will be worked out in a more direct way than in previous work. Electric field thresholds and growth rates for parametric instabilities will be obtained from theory of homogeneous Mathieu equation. Stationary excitation at the driving frequency and its harmonics follows from a particular solution of an inhomogeneous Mathieu equation.     

Spectral Gap and Exponential Decay of Correlations

We study the relation between the spectral gap above the ground state and the decay of the correlations in the ground state in quantum spin and fermion systems with short-range interactions on a wide class of lattices. We prove that, if two observables anticommute with each other at large distance, then the nonvanishing spectral gap implies exponential decay of the corresponding correlation. When two observables commute with each other at large distance, the connected correlation function decays exponentially under the gap assumption. If the observables behave as a vector under the U(1) rotation of a global symmetry of the system, we use previous results on the large distance decay of the correlation function to show the stronger statement that the correlation function itself, rather than just the connected correlation function, decays exponentially under the gap assumption on a lattice with a certain self-similarity in (fractal) dimensions D < 2. In particular, if the system is translationally invariant in one of the spatial directions, then this self-similarity condition is automatically satisfied. We also treat systems with long-range, power-law decaying interactions.     

Wave Instabilities of a Collisionless Plasma in Fluid Approximation

Wave properties and instabilities in a magnetized, anisotropic, collisionless, rarefied hot plasma in fluid approx‐imation are studied, using the 16‐moments set of the transport equations obtained from the Vlasov equations. These equations differ from the CGL‐MHD fluid model (single fluid equations by Chew, Goldberger, and Low [5,9]) by including two anisotropic heat flux evolution equations, where the fluxes invalidate the double polytropic CGL laws. We derived the general dispersion relation for linear compressible wave modes. Besides the classic incompressible fire hose modes there appear four types of compressible wave modes: two fast and slow mirror modes – strongly modified compared to the CGL model – and two thermal modes. In the presence of initial heat fluxes along the magnetic field the wave properties become different for the waves running forward and backward with respect to the magnetic field. The well known discrepancies between the results of the CGL‐MHD fluid model and the kinetic theory are now removed: i) The mirror slow mode instability criterion is now the same as that in the kinetic theory. ii) Similarly, in kinetic studies there appear two kinds of fire hose instabilities ‐ incompressible and compressible ones. These two instabilities can arise for the same plasma parameters, and the instability of the new compressible oblique fire hose modes can become dominant. The compressible fire hose instability is the result of the resonance coupling of three retrograde modes ‐ two thermal modes and a fast mirror mode. The results can be applied to the theory of solar and stellar coronal and wind models (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stark Broadening of Ne II and Ne III Spectral Lines

Using a semiclassical approach, the widths and shifts of the spectral lines of three Ne II and six Ne III multiplets caused by collisions with electrons, protons, and helium ions at a density of perturbing particles of 10¹⁷ cm^–3 and different temperatures have been calculated. The results obtained have been compared with the known experimental and theoretical data.     

利用光学-光学双共振研究谱线的碰撞增宽

利用光学-光学双共振光谱技术研究了NaK分子21Σ＋→６1Σ＋跃迁线的碰撞增宽。一台单模半导体激光器实现11Σ＋(v″,J″)→21Σ＋(v′,J′)的跃迁,另一单模半导体激光器激发21Σ＋(v′,J′)能级到６1Σ＋的振转能级,二激光束反向平行通过样品池。谱线总线宽与K原子密度成线性关系,由其斜率得到增宽速率系数k_br＝(1.4±0.7)×10-8 cm3·s-1。同时研究了21Σ＋(v＝8,J＝12)→21Σ＋(v＝8,J＝13,14)转动能级间的碰撞激发转移,测量谱线的相对强度,由速率方程得到碰撞转移速率分别为6.1×106和5.2×106 s-1。     

Simulation of Internal Gravity Wave Propagation Due to Sudden Stratospheric Warming

The results of modeling the effect of stratospheric internal gravity waves (IGWs) excited in the region of sudden stratospheric warming (SSP) on the state of the upper atmosphere are presented. The numerical experiment used a two-dimensional model of atmospheric wave propagation including the dissipative and nonlinear processes accompanying the wave propagation. As a perturbation source, perturbations of temperature and density in a localized region at stratospheric altitudes during the SSW were considered. The amplitude and frequency of the perturbation source were evaluated from the results of observations and IGW theory. The results of numerical calculations showed that the heat source localized in the stratosphere excites IGWs with periods of up to several hours, which reach the thermospheric altitudes within a few hours. The maximum relative perturbations created by these waves relative to the unperturbed conditions were noted at altitudes of 100–200 km and at distances of up to ~1000 km from the source center.     

Dramatic Spectral Broadening of Ultrafast Laser Pulses in Molecular Nitrogen Ions

We investigate nonlinear interaction of nitrogen molecules with a two-color laser field composed by an intense800 nm laser pulse and a weak 400 nm laser pulse.It is demonstrated that the spectrum of 400 nm pulses is dramatically broadened when the two beams temporally overlap.In comparison,the spectral broadening in argon is less pronounced,although argon atoms and nitrogen molecules have comparable ionization potentials.We reveal that the dramatic spectral broadening originates from the greatly enhanced nonlinear optical effects in the near-resonant condition of interaction between the 400 nm pulses and the nitrogen molecular ions.     

微波铁氧体损耗的晶粒表层自旋波共振模型

考虑了晶粒表层中由杂质和应力引起的感生单轴各向异性场,由进动方程解出了晶粒表层中的自旋波体征频率.通过比较晶粒内部和表层的自旋波频谱上、下限,说明了非共振有效线宽ΔHeff来源于晶粒表层的自旋波共振激发.提出的多晶内禀磁化率χi+由晶粒内部的χb+和晶粒表层的χs+所组成,得出了非共振ΔHeff与χs″+及晶粒表层体积分数Vs成正比的关系式.解释了ΔHeff与晶粒尺寸及气孔率的关系.阐明了场移的物理机制,理论与实验相符. 关键词：     

光子回声量子存储器中非均匀展宽频谱对存储效率的影响

本文提出了一个利用光子回声技术探究非均匀展宽频谱线形(如高斯、洛伦兹分布)对存储效率影响的简捷方法。我们发现当信号光脉冲的持续时间与介质频谱线宽的乘积远大于1时,可将分布函数的傅里叶变换近似成狄拉克函数,使得研究非均匀展宽频谱对存储效率的影响变得非常容易;通过计算发现不同线形分布达到最佳存储效率的光学深度有所不同,频谱线形趋于均匀时达到最优存储效率的存储介质光学深度最小。该研究对实验上实现最优化光量子态存储具有指导意义。     

Experimental Evidence of Parametric Instabilities in an Unmagnetized Plasma Subjected to a Strong H.F. Electric Field

Experimental evidence of parametric excitation, by an intense external H.F. field, of an electron surface mode and an ion wave is presented. The pumping electromagnetic energy density is equal to or slightly larger than the thermal energy density of the electrons. The value of f_pc/f₀ (electron plasma frequency/external field frequency) is that for an electron surface wave. Depending on the pressure and field intensity, this decay instability can lead to three types of low frequency oscillations, with frequencies close to the ion plasma frequency. Two of these are described by Aliev and Silin's intense field theory: one is the volume ion plasma oscillation and the other a surface ion plasma oscillation. The third corresponds to no known ion eigenmode. Several other features of the theory by Aliev and co-workers are also confirmed experimentally, such as the harmonic excitation of the instability (nf₀ ≈ f_pe/√2, where n is an integer), the instability amplitude as a function of f_pe/f₀ (above threshold conditions), the value of the mismatch parameter as a function of field strength and ion mass, and the existence of a fine structure corresponding to the symmetric and antisymmetric electron surface oscillations. Even at high pump field strengths, the decay products are nearly monochromatic i.e. the plasma does not become turbulent.     

Dark Spatial Solitary Wave Due to Cascaded x(2) Nonlinearity

The formation of the dark spatial solitary wave in cascaded second harmonic generation processes is numerically studied based on the nonlinear-coupled equations. It is shown that the solitary wave exists when the effective three-order nonlinearity induced by cascaded second-order nonlinearity is negative.     

Parametric Instabilities of Two Kind of Millimeter Waves and Multiplication of Frequency in GaAs Semiconductors

This paper deals, at first, with the non-linear parametric effects on both space charge and electromagnetic waves in GaAs semiconductors. If an external electric field is applied, at the critical field value, the mobility changes its sign and becomes negative, as a result, non-linear instabilities of the interactions are obtained. At the optimal value of electric field, E _opt, all non-linear processes are very effectives. The second point is the multiplication of the wave frequency, which is also effective thanks to the non-linearity. This process is used for carring waves into millimeter range instead of generation process, which in this range is non-effective. The Multiplication effect is based on the using space charge waves.