The Spectral Intensity of the Plasma of Single and Double Laser Pulses

We compare radiation of plasma flares produced on exposure of metals to laser radiation in a monopulse generation mode in the case of single and double pulses with change in air pressure. For double pulses, we established an increase in the duration and intensity of the radiation of spectral lines and also an analogy between the change in their intensities and those of single pulses obtained at a reduced air pressure.     

强激光在窄通道中传播的理论研究

在考虑相对论和有质动力非线性以及全局电量守衡的前提下,分析了强激光在冷等离子体窄通道中稳定传播的情况。采用较为简化的二维理论模型,给出了描述激光和通道横向结构的解,对不同通道宽度、通道密度、激光强度和电磁模式等进行了讨论,分析了其对激光在等离子体通道中传播的影响。分析发现,在存在预通道的情况下,当等离子体通道的密度大于临界密度很多时(例如20倍临界密度),即使是在激光波长量级的通道中,激光仍然可以传播。通道越宽,等离子体密度越小;激光强度越大越容易传播。在同样的通道和传输情况下,TE0模传输所需要的激光强度比TE1模要小。     

强激光等离子体耦合效应的数值模拟

 研究了高强度（10¹²(10^{14W/cm2）,纳秒脉冲(高斯型)激光与AI、 CH等离子体的耦合效应。采用一维双温、单流体力学方程组,数值模拟研究激光强度和波长对靶表面能量沉积和对等离子体特征参数的影响。激光等离子体耦合的主要机制有:轫致辐射、逆轫致辐射吸收、热扩散和电子、离子之间碰撞能量交换。给出了电子最高温度与光强的近似定量关系。}     

外加高压电场下空气中激光等离子体通道寿命研究

通过对飞秒激光在空气中产生的等离子体通道两端外加高压,来研究通道的寿命变化情况。实验得到,当在等离子体通道两端外加高压时(350 kV/m),等离子体通道寿命延长了近3倍。理论模拟和分析结果表明在外加电场条件下,碰撞电离得到增强,吸附作用相对减弱,解离复合系数随着电子平均能量的增加而下降的趋势更为剧烈,这进一步引起了等离子体通道寿命的延长。实验结果与理论分析共同表明了利用外加电场对空气中激光等离子体通道寿命进行延长的可行性。     

Study of Laser Induced Plasma at Low Laser Intensity

Laser induced plasma in the intensity range 8.106-109 is studied. It is observed that the electron temperature of the plasma increases with laser intensity while the electron density increases up to certain laser intensity, beyond which it decreases and then saturates.     

超短超强激光和稠密等离子体相互作用的数值研究

应用一维粒子模拟方法数值研究了超短超中激光和稠密等离子体的相互作用，结果表明，在等离子体中的激发起无规则的电场波动，同时在等离子体中产生温度很高的电子。     

Amplification and Guiding of Microwave Radiation in a Plasma Channel Created by an Ultrashort High-Intensity Laser Pulse in Noble Gases

We develop an analytical model of the evolution of a plasma channel produced in rare gases (argon and xenon) by a femtosecond KrF laser pulse. We show that the strong nonequilibrium of the photoelectron energy spectrum and the presence of the Ramsauer minimum in the transport scattering cross section makes the channel optically more dense as compared to the non-ionized gas in the microwave frequency band, and consequently such a channel appears to be a waveguide. In xenon, this nonequilibrium state of the plasma leads to the transportation and amplification of the microwave signal during the relaxation process of the photoelectron energy spectrum.     

Laser Mode-Dependent Size of Plasma Zones Induced by Femtosecond Laser Pulses in Fused Silica

We carry out the numerical simulations of femtosecond laser propagation with TEMoo mode, TEM10 mode and a beam combining both the modes in fused silica. It is found that the transverse size of plasma zones induced by laser pulses with the TEM10 mode is smaller than that induced by the TEM00 mode, while the longitudinal size is almost the same, and the saturated plasma density is higher. The transverse size, the longitudinal size and the ratio of the longitudinal to transverse size, for the beam combining both the modes, all could be reduced at the same time in comparison with the TEM00 mode under the same focusing conditions.     

Approximated Vector Potential of Intense Laser Pulses in a Pair Plasma

A （3＋1 ）-dimensional Kadomtse-Petviashvili （KP） equation for nonlinearly interacting intense laser pulses with an electron-positron （e-p） plasma is derived. Taking into account the combined action of the relativistic particle mass increase and the relativistic light ponderomotive force, using the perturbation method, and allowing different types solution, we discuss the analytical solution of （3＋1）-dimensional KP-I equation, and give the approximate solutions of vector potential of the intense laser pulse in e-p plasma. Our results may be significantly useful in understanding the nonlinear wave propagation and interaction of intense laser beams in an e-p plasma.     

超短超强激光与稀薄等离子体相互作用的数值研究

用一维粒子模拟方法（Ｐａｒｔｉｃｌｅ－ｉｎ－Ｃｅｌｌ）数值研究了超短超强激光（Ｉλ＾２〉１０＾１８Ｗ．μｍ＾２／ｃｍ＾２）与稀薄等离子体的相互作用过程，结果表明，超短超强激光与稀薄等相互作用后，在等离子体中激发起尾波和拉曼（Ｒａｍａｎ）波，它们的波长和频率的值与解析解符合得很好；同时在尾波的作用下，等离子体的部分电子被加速的很高的速度，甚至接近光速。     

飞秒和纳秒激光脉冲作用下等离子体X射线辐射特性

对飞秒和纳秒激光作用下的Ａｌ和Ｃｕ等离子体的Ｘ射线辐射进行了测量、分析和比较．实验结果表明在飞秒激光脉冲下等离子体Ｘ射线峰值向短波方向移动．同时Ａｌ等离子体的的电离阶数和温度在飞秒下比纳秒高．     

基于泵浦脉冲诱导等离子体通道的空心光束产生

利用飞秒脉冲诱导生成的具有渐变折射率分布的等离子体通道产生空心光束.当飞秒脉冲在非线性介质中传输时将电离产生等离子体通道,该等离子体通道具有渐变的折射率分布,等离子体通道中激光束只能在电子密度低于临界等离子体密度的区域传播,故当探测光束在等离子体通道边缘传输时将偏转形成空心光束.当泵浦光束功率为8mW时,探测光束转变为典型的空心光束结构;当泵浦光束的入射功率、重复率或等离子体通道中轴向电子密度改变时,等离子体通道中可供探测光束通过的区域将随之发生改变,这将导致空心光束中黑斑的面积发生变化.因此通过调节泵浦光束的入射功率和重复率可以控制产生空心光束的黑斑大小.     

对超短脉冲激光引雷产生的等离子体通道的特性分析

 利用隧道电离诱导闪电模型,对超短脉冲激光在大气中产生弱等离子体通道的电阻和阈值强度进行了分析和计算。结果显示：强度为10¹⁴ W/cm²量级的超短脉冲激光产生的气体等离子体通道有较好的导电性,所需激光能量很小, 说明在该模型下激光能量的利用效率很高。     

激光诱导等离子体光谱空间分布特性

激光波长和激光入射角是影响激光诱导等离子体空间分布和光谱强度空间分布特性的重要因素.基于流体动力学和SAHA方程,仿真了激光诱导等离子体的二维空间演化过程,研究了激发等离子体的辐射光谱空间分布特性及激光波长、入射角度等参数对等离子体特征谱线空间分布特性的影响.研究结果表明:波长为1064 nm的激光在不同延时条件下,最佳激光入射角度均为0°.当入射角度为0°时,所激发的等离子体辐射在不同的探测角度处均有较强的光谱信号,且在100,500,1000 ns延时条件下,最佳探测角分别为±41°、±11°和±12°.对于不同的波长,当延时分别为100 ns和500 ns且激光以0°入射时,长波长激光所激发的等离子体光谱在不同探测角处的强度均强于短波长激光.当延时为100 ns时,1064 nm波长激光所激发的光谱在最佳探测角位置的强度约为532 nm和266 nm波长激光所激发的光谱在各自最佳探测角位置强度的2倍.随着探测角绝对值的减小,等离子体辐射光谱强度先增大,到达最佳探测角后强度再减小.入射波长分别为532 nm和1064 nm的激光诱导击穿光谱实验结果验证了仿真结果.     

Spatiotemporal Evolution of Intense Short Gaussian Laser Pulses in Weakly Relativistic Magnetized Plasma

The weakly relativistic regime of propagation of a short and intense laser pulse in the magnetized plasma is investigated. By considering relativistic nonlinearity and using non‐linear Schrödinger equation with paraxial approximation, two second‐order coupled differential equations are obtained for the longitudinal pulse width parameter (in time) and for the transverse pulse width parameter (in space). The simultaneous evolution of spot size and length of a relativistic Gaussian laser pulse in a magnetized plasma can be calculated by the numerical solution of the equations. The effect of magnetic field is investigated. It is observed that in the presence of magnetic field both the self‐compression and the self‐focusing can be enhanced. Furthermore, the interplay between the longitudinal self‐compression and the transverse self‐focusing in a magnetized plasma is investigated. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Radiative Losses of Plasma on Interaction of Ultrashort Laser Pulses with Matter

Radiative losses of plasma produced by ultrashort laser pulses near the surface of solid targets were studied by the methods of highresolution xray spectroscopy and using the numerical simulation of gasdynamics and radiation processes. The experiments were carried out at the NEODIM laser facility in the Central Research Institute for Machine Building. The flux density was as high as 10¹⁷ W/cm² when the radiation was focussed onto the surface of solid targets from Al and Cu. The timeintegrated discrete spectra of plasma of the multiply charged ions were recorded in the soft xray band from 0.8 to 3.0 keV. The experimental spectra were compared with the results of numerical calculations within the framework of the model, which considered both hydrodynamic and radiationcollisional processes. The association of the radiation dynamics of the individual groups of lines with the spatial and temporal dynamics of the laser torch was revealed. Such an association permits one to judge the nonstationary processes in the expanding plasma even by the spectra integrated over time. From comparison of the experimental results and model calculations, it follows that the line emission of a relatively narrow (in the charge number) group of ions constitutes the major portion of radiation losses.     

高能量高峰值功率激光系统的稳定性问题研究

针对高能量高峰值功率激光系统建立了相应的理论分析模型和计算程序,并针对放大系统的稳定性进行了分析,同时还对放大链路中的B积分、频谱漂移、泵浦光和信号光之间的时间同步抖动进行了模拟分析.分析结果表明：采用两级放大结构,有利于提高系统的稳定性;同时需要严格控制全系统B积分累积,建议全系统B积分的累积值小于2,超过2的B积分累积意味着更多的注入能量,如果泵浦光和信号光之间的同步时间抖动控制在±0.2 ns之内,输出稳定性可控制在rms2％之内.     

高重复频率激光等离子体软X光脉冲探测

研制了一种高重复频率小型激光等离子体软Ｘ光脉冲探测装置，给出其设计原理和性能参量，采用光谱学诊断方法研究了光源的软Ｘ射线辐射特性，得到了一些新的实验结果