有质动力对超短脉冲激光与固体等离子体相互作用的影响

通过测量由等离子体临界面移动造成的反射激光的频移,研究了有质动力对超短脉冲激光与固体等离子体相互作用的影响。实验表明,当激光强度达到1017 W/cm2时,有质动力将明显地降低等离子体热膨胀速度,造成极陡的密度分布,使得等离子体中的主导吸收机制,由共振吸收转换为真空吸收。     

有质动力对超短脉冲激光与固体等离子体相互作用的影响

 通过测量由等离子体临界面移动造成的反射激光的频移，研究了有质动力对超短脉冲激光与固体等离子体相互作用的影响。实验表明，当激光强度达到10¹⁷ W/cm²时，有质动力将明显地降低等离子体热膨胀速度，造成极陡的密度分布，使得等离子体中的主导吸收机制，由共振吸收转换为真空吸收。     

Particle simulation on electron acceleration process by the laser ponderomotive force in inhomogeneous underdense plasma layers

The mechanism of electron ponderomotive acceleration due to increasing group velocity of laser pulse in inhomogeneous underdense plasma layers is studied by two-dimensional relativistic parallel particle-in-cell code. The electrons within the laser pulse move with it and can be strongly accelerated ponderomotively when the duration of laser pulse is much shorter than the duration of optimum condition for acceleration in the wake. The extra energy gain can be attributed to the change of laser group velocity. More high energy electrons are generated in the plasma layer with descending density profile than that with ascending density profile. The process and character of electron acceleration in three kinds of underdense plasma layers are presented and compared.     

有质动力和静电分离场对激光等离子体流体力学状态的影响

利用建立在欧拉坐标系上的一维电子_离子双流双温流体力学程序, 模拟了超短脉冲强激光 (1×1015W/cm2, 150fs)与线性密度梯度等离子体相互作用的流体力学过程. 模拟结果显示，入射激光与临界密度面的反射光叠加，在临界密度以下区域形成局域驻波， 产生的强有质动力在低密区驱动电子形成周期性密度结构——Bragg光栅，激光的反射被增 强. 临界密度处有质动力将等离子体分成向内和向外运动的两部分. 由于离子所受的有质动 力和热压强的梯度力远小于电子，体系产生了强静电分离场，离子的运动主要由该静电分离 场决定. 对双流双温模型和单流双温模型的模拟结果进行了比较. 当有质动力和热压强梯度 力较大时，两种模型对等离子体流体力学状态的描述有明显差异，单流双温模型无法描述此 时的流体力学状态. 关键词： 有质动力 密度调制 双流双温流体力学模型 单流模型     

Effects of relativistic and ponderomotive nonlinearities on the interaction of high-power laser beam with an inhomogeneous warm plasma

The influence of relativistic-ponderomotive nonlinearities and the plasma inhomogeneity on the nonlinear interaction between a high-power laser beam and a warm underdense plasma are studied. It is clear that the relativistic ponderomotive force and the electron temperature modify the electron density distribution and consequently change the dielectric permittivity of the plasma. Therefore, by presenting the modified electron density and the nonlinear dielectric permittivity of the warm plasma, the electromagnetic wave equation for the propagation of intense laser beam through the plasma is derived. This nonlinear equation is numerically solved and the distributions of electromagnetic fields in the plasma, the variations of electron density, and plasma refractive index are investigated for two different background electron density profiles. The results show that the amplitude of the electric field and electron density oscillations gradually increase and decrease, during propagation in the inhomogeneous warm plasma with linear and exponential density profiles, respectively, and the distribution of electron density becomes extremely sharp in the presence of intense laser beam. It is also indicated that the electron temperature and initial electron density have an impact on the propagation of the laser beam in the plasma and change the plasma refractive index and the oscillations' amplitude and frequency. The obtained results indicate the importance of a proper choice of laser and plasma parameters on the electromagnetic field distributions, density steepening, and plasma refractive index variations in the interaction of an intense laser beam with an inhomogeneous warm plasma.     

Effect of polarization force on the Jeans instability of self-gravitating dusty plasma

The effect of polarization force acting on massive charged dust grains is investigated analytically on the Jeans instability of self-gravitating dusty plasma. The gravitational force acting on the massive negatively charged interstellar dust grains are considered in presence of both electrical and polarization forces. The basic equations of the problem are formulated and a general dispersion relation is obtained using plane wave approximation in low frequency wave mode. The effect of polarization force in the dispersion relation of the problem, condition of the Jeans instability and expression of the critical Jeans wave number is examined. The unstable growing modes due to self-gravitational force are studied in the situation when polarization force on the dust grain exceeds over the electrical force in magnitude. It is observed that the polarization force increases the growth rate of the system.     

Insights into the Maillard reaction. The mechanism of Schiff's base formation from the reaction force perspective

Schiff's base formation of the Maillard reaction is described from a theoretical viewpoint. The double proton transfer reaction was investigated within the frame of reaction force analysis in which global and local electronic properties were monitored within reaction regions defined along the reaction coordinate. Calculations based on density functional theory show that Schiff's base formation in the Maillard reaction occurs through an asynchronous double proton transfer, the second proton transfer being the determinant step of the reaction.     

具有分布损耗波导结构的回旋行波放大器绝对不稳定性

 详细推导了具有分布损耗波导结构的回旋行波放大器的色散特性。通过绝对不稳定性振荡出现的条件,给出求解具有损耗波导结构回旋行波管放大器的绝对不稳定性起振电流的数值计算方法。研究结果表明：绝对不稳定性起振电流与损耗波导的集肤深度有关,选择有较大的集肤深度的损耗波导可以提高绝对不稳定性起振电流;绝对不稳定性起振电流同时也与工作磁场偏离饱和磁场的程度以及电子束的纵横速度比有关;通过设计具有分布损耗波导结构的注-波互作用电路,以及工作磁场、电子束的纵横速度比,可以在兼顾带宽、效率的条件下,保证回旋行波管放大器稳定工作。     

Modulation instability in silicon optical waveguide considering linear loss

Taking into account the linear loss of silicon-on-insulator (SOI) waveguide, modulation instability (MI) induced by combined effects of self-phase modulation and waveguide dispersions is investigated. The impacts of various parameters to gain spectra of MI are analyzed theoretically, and direct numerical simulation of nonlinear Schroedinger equation is performed as well. Results show that strong MI takes place even in the existence of low light power. The linear loss of waveguide obviously impacts gain spectra of MI, even within ultra-short propagation distance. The peak gain frequency and bandwidth of gain spectra decrease to 41.683% and 41.6879% of their maximum at propagation distance z = 5 mm, respectively.     

具有分布损耗波导结构的回旋行波放大器绝对不稳定性

详细推导了具有分布损耗波导结构的回旋行波放大器的色散特性。通过绝对不稳定性振荡出现的条件,给出求解具有损耗波导结构回旋行波管放大器的绝对不稳定性起振电流的数值计算方法。研究结果表明：绝对不稳定性起振电流与损耗波导的集肤深度有关,选择有较大的集肤深度的损耗波导可以提高绝对不稳定性起振电流;绝对不稳定性起振电流同时也与工作磁场偏离饱和磁场的程度以及电子束的纵横速度比有关;通过设计具有分布损耗波导结构的注-波互作用电路,以及工作磁场、电子束的纵横速度比,可以在兼顾带宽、效率的条件下,保证回旋行波管放大器稳定工作。     

Generation of Optical and Mechanical Squeezing in the Linear‐and‐Quadratic Optomechanics

Generation of strong stationary optical and mechanical squeezing is proposed for the linear‐and‐quadratic optomechanical system, where two cavity modes induce linear and quadratic optomechanical couplings, respectively. Through the linearization treatment, linearized coupling between cavity mode and mechanical mode and the mechanical parametric amplification process are achievable and controllable by independent driving lasers. Optical and mechanical squeezing are generated following different mechanisms. Optical squeezing works in the strong coupling regime, and mechanical amplification would push the system close to instability threshold, which could deeply improve ponderomotive squeezing even significantly beyond the 3 dB squeezing limit. Mechanical squeezing is generated based on the reservoir engineering method, where parametric amplification induces the squeezing transformation of mechanical mode; and linearized coupling, which operates in the red‐sideband and weak coupling limits, induces the ground‐state cooling of transformed mechanical mode. Finally, the original mechanical mode would be squeezed, which could also exceed 3 dB limit.     

漫谈惯性力

作者对在本刊发表的多篇与惯性力有关文章的梳理.     

ps参量放大效应

本文报道用0.53μm波长超短脉冲序列泵浦角度调谐的LiNbO_3参量晶体,获得1%单程参量放大能量转换效率,并在0.8～1.6μm范围测得参量信号光和空载光波长调谐曲线.     

Feedback stabilization of drift cyclotron loss cone instability by modulated electron sources

It is shown that the drift cyclotron loss cone instability can be suppressed by modulating electron density within the plasma. With the feedback in +90° phase the critical density gradient needed for the onset of the drift cyclotron loss cone instability increases approximately linearly with the gain. Typically with the gain of −50Ω _i the critical density gradient can be pushed up by as much as two orders of magnitude and minimum mirror plasma radius can be brought down in the same proportion.     

Oscillatory thermal-diffusive instability of combustion waves in a model with chain-branching reaction and heat loss

In this paper we investigate the properties and the linear stability of premixed combustion waves in a non-adiabatic thermal-diffusive model with a two-step chain-branching reaction mechanism. Here we focus only on the emergence of the pulsating instabilities, and the stability analysis is carried out for Lewis numbers for fuel greater than one, and various values of Lewis number for radicals. We consider the problem in two spatial dimensions to allow perturbations of a multidimensional nature. It is demonstrated that the flame speed as a function of the parameters is a double-valued C-shaped function, i.e. for a given set of parameter values there are either two solutions, fast and slow solution branches, propagating with different speed, or the combustion wave does not exist. The extinction of combustion waves occurs at finite values of the parameters and non-zero flame speed. The flame structure demonstrates a slow recombination regime behaviour with negligible fuel leakage for the fast solution branch away from the extinction condition. For parameter values close to the extinction condition and on the slow solution branch, the fuel leakage is significant and a fast recombination regime is observed. It is demonstrated that two types of instabilities emerge in the model: the uniform planar and the travelling instability. The slow solution branch is always unstable due to the uniform perturbations. The fast solution branch is either stable or loses stability due to the travelling or uniform perturbations. The switching between the onset of various regimes of instability is due to the bifurcation of co-dimension two. In the adiabatic limit this bifurcation is found for Lewis number for fuel equal to one, whereas in the non-adiabatic case it moves towards values above unity. The properties of the travelling instability are studied in detail.     

Analysis of parametric oscillatory instability in Fabry-Perot cavity with Gauss and Laguerre-Gauss main mode profile

We calculate the parametric instabilities in Fabry-Perot cavities of advanced VIRGO and LIGO interferometers with different main mode profiles. All unstable combinations of elastic and Stokes modes both for the case with TEM₀₀ and LG₃₃ as a carriers are deduced.     

Asymptotic solutions for Mathieu instability under random parametric excitation and nonlinear damping

A theoretical analysis is presented of the response of a lightly and nonlinearly damped mass-spring system in which the spring constant contains a small randomly fluctuating component. Damping is represented by a combination of linear and nonlinear power-law damping. System response to some initial disturbance at time zero is described by a sinusoidal wave whose amplitude and phase vary slowly and randomly with time. Leading order formulations for the equations of amplitude and phase are obtained through the application of methods of stochastic averaging of Stratonovich. The equations of amplitude and phase are given in two versions: Fokker-Planck equations for transient probability and Langevin equations for response in the time-domain. Solutions in closed-form of these equations are derived by methods of mathematical and theoretical physics involving higher transcendental functions. They are used to study the behavior of system response for ever increasing time applying asymptotic methods of analysis such as the method of steepest descent or saddle-point method. It is found that system behavior depends on the power density of the parametric excitation at twice the natural frequency and on the magnitude and form of the damping. Depending on these parameters different types of system behavior are found to be possible: response which decays exponentially to zero, response which leads to a stationary state of random behavior, and response which can either grow unboundedly or which approaches zero in a finite time.     

The effect of a coriolis force on Taylor-Couette flow

Taylor-Couette flow subject to a Coriolis force is studied experimentally and numerically. In the experiment, the Couette apparatus is mounted on a turntable with the axis of the cylinders orthogonal to the rotation vector of the turntable. The Coriolis force stabilizes the fluid against the onset of Taylor vortices and alters the velocity fields, both above and below the transition from the initial flow. At small dimensionless turntable frequencies, the transition yields time-independent Taylor vortices which are tilted with respect to the cylinder axis. At larger there is a direct transition to turbulence. We determine the first-order correction to the classical Couette initial flow, to account for the effects of the Coriolis force, by expanding in powers of. We present numerical results for the axial velocity (the only nonvanishing correction term to order) in the infinite-cylinder approximation.     

双折射光纤中拉曼效应对参量放大增益谱的影响

根据激光脉冲在光纤中传输时, 所满足的波动方程, 导出了拉曼效应和参量放大共同作用下, 在双折射光纤中所遵循的耦合模方程, 并引入平行拉曼增益的洛伦兹模型, 给出了输入抽运波偏振方向同双折射轴成45^o 时, 拉曼效应和参量放大共同作用所导致的增益. 讨论并分析了拉曼效应在不同色散区对参量放大增益谱的影响. 结果表明, 在考虑拉曼效应后, 使得参量放大斯托克斯波与反斯托克斯波增益谱彼此不对称; 在反常色散区, 产生的增益以反斯托克斯波为主, 正常色散区则以斯托克斯波为主.