激光等离子体的辐射与自吸收现象研究

脉冲强激光辐照固体靶材时,会讯速地在靶材表面形成一个高高压的等离子体区哉。该等离子体区域在吸收入射激光的同时,会发出很强的紫外以至ｘ光辐射,它们与靶材有着更强的耦合。本文给出了等离子体中辐射传输的微分方程,并通过对等离子体中辐射和自吸收现象进行讨论,给出了在考虑再辐射效应时,等离子体辐射能流与等离子体参数及激光参数的关系。     

椭圆偏振激光在等离子体中的调制不稳定性

为了研究椭圆偏振激光在等离子体中的调制不稳定性,采用洛伦兹技巧推导出椭圆偏振激光在等离子体中的非线性色散关系,基于横波所满足的非线性控制方程,分析了有限振幅的扰动态引起的调制不稳定性,得到了调制不稳定的时间增长率与扰动态波数之间的函数关系,并对等离子体中不同区域的调制增长率进行了比较。结果表明,激光等离子体的临界面附近的调制不稳定性的时间增长率较激光等离子体中其余位置处更为显著。     

Self-focusing and guiding of short laser pulses in ionizing gasesand plasmas

Several features of intense, short-pulse (≲1 ps) laser propagation in gases undergoing ionization and in plasmas are reviewed, discussed, and analyzed. The wave equations for laser pulse propagation in a gas undergoing ionization and in a plasma are derived. The source-dependent expansion method is discussed, which is a general method for solving the paraxial wave equation with nonlinear source terms. In gases, the propagation of high-power (near the critical power) laser pulses is considered including the effects of diffraction, nonlinear self-focusing, ionization, and plasma generation. Self-guided solutions and the stability of these solutions are discussed. In plasmas, optical guiding by relativistic effects, ponderomotive effects, and preformed density channels is considered. The self consistent plasma response is discussed, including plasma wave effects and instabilities such as self-modulation. Recent experiments on the guiding of laser pulses in gases and in plasmas are briefly summarized     

Plasma electronics in pulsed nitrogen lasers

A detailed study showing that the electronic impedances of both the spark gap and the laser channel plasmas play an integral part in the overall discharge circuit of a pulsed nitrogen laser is presented. The electronic properties of these plasmas can critically determine the temporal width of the laser pulse     

超短高功率脉冲激光与物质相互作用及其应用

超短高功率脉冲激光系统的小型化实用化极大地促进了激光与物质相互作用的物理和应用研究。回顾加拿大魁北克大学国立科学研究院材料研究所（简称ＩＮＲＳ）的超短高功率脉冲激光产生高温高密度等离子体的最新研究成果及其在分子物理和辐射约束高温高密度等离子体物理中的应用。     

通过圆偏振光提高飞秒激光诱导击穿光谱的发射强度

激光诱导击穿光谱(LIBS)是一种快速、实时的元素成分分析技术。为了提高LIBS的灵敏度,人们已经提出多种方法来提高LIBS的光谱强度。本文采用飞秒脉冲激光烧蚀黄铜产生LIBS,对比了圆偏振和线偏振下LIBS光谱的强度,结果发现圆偏振下的光谱强度比线偏振下的强,光谱强度大约提高了15%。采用飞秒激光照射金属时,金属内部的自由电子吸收光子的能量。在线偏振飞秒激光场中,电子在脉冲的每个光学周期中经历交替的加速和减速;而圆偏振飞秒激光可以连续加速电子,因此电子可以获得更高的能量,这使得圆偏振飞秒激光产生的光谱强度不同于线偏振飞秒激光产生的光谱强度,圆偏振激光有助于改善飞秒LIBS信号的强度。     

平面型有界等离子体的不稳定性

激光与平面型等离子体相互作用,会出现各类非线性过程。本文从等离子体中两个波耦合方程出发,研究了均匀等离子体的不稳定性。当存在阻尼时,就有可能出现不稳定性。而当阻尼很小可被忽略后,将仅出现空间增益效应。对于密度按线性变化的非均匀等离子体,本文得到它的解析解,并讨论了出现不稳定性的条件。     

“点投影”keV波段X射线吸收谱的实验技术研究

报道了一项高密度激光等离子体ｋｅＶ波段Ｘ射线吸收谱工作。实验上采用称为＂点投影（ＰｏｉｎｔＰｒｏｊｅｃｔｉｏｎ）＂的靶场光学方案，成功地获得了高空间分辨（＜２４μｍ）的类氦铝１ｓ２－１ｓ２ｐ及类氖锗２ｐ－３ｄ共振吸收谱信号，为Ｘ激光及激光核聚变研究提供了一种新的参量诊断方案。     

用激光激励的Xe等离子体复合激光器

本文报导了以波长10.6微米的CO_2激光脉冲,在H_θ与X_θ的混合气体中产生X_θ等离子体复合激光器。     

激光诱导Al等离子体中电子密度和温度的实验研究

激光烧蚀等离子体在微量元素分析方面有着重要的应用背景，而缓冲气体的种类及压力对激光等离子体的特性有重要影响。报道了以氦气、氩气、氮气和空气作为缓冲气体，实验测定了不同气压下Nd：YAG激光烧蚀Al靶产生的等离子体中的时间分辨发射光谱，利用发射谱线的Stark展宽和相对强度计算了等离子体中的电子密度和温度，得到了在不同缓冲气体中激光诱导Al等离子体的电子密度随延时、气压的演化规律，同时得到了电子温度的时间演化特性。实验结果表明，电子密度的数量级约为10^17cm^-3，电子温度测量值约为10000K，二者都是在激光脉冲后随时间快速衰减，直到4μs以后达到一个较低的水平并缓慢变化，其中以氩气作为缓冲气体时等离子体中的电子密度最大。     

环境气体中激光诱导Fe等离子体发射光谱的时间演化特性

环境气体对于激光诱导等离子体的形成和演化特征有着重要影响,适当的环境气体条件有利于激光诱导等离子体发射光谱分析的进行。利用准分子激光(308 nm)烧蚀低合金钢靶诱导等离子体原子发射光谱,研究了环境气体对等离子体发射光谱强度及时间演化特性的影响,对实验结果进行了讨论,得到了激光诱导Fe等离子体的原子发射光谱分析的优化条件。实验测定了不同气压氩气、氦气环境下及真空条件下Fe等离子体发射光谱强度及时间演化特性。结果表明,环境气体对激光诱导Fe等离子体发射光谱具有增强作用,而在较低气压下氩气比氦气的辐射增强效果更为显著。在5.32×104Pa氩气环境下,在等离子体形成后约6μs和10μs时发射谱线强度和信号背景比分别达到最大值。     

A 28 μm water-vapor laser interferometer for plasma diagnostics

A high-power CW 27.972 μm water-vapor laser has been developed for interferometric and polarimetric measurements of plasmas. The maximum output power and the power density in the cavity of the laser with 2.0 cm bore and 220 cm length reach 85 mW and 109 μW/cm³, respectively. An interferometer using this laser is constructed and its performance is examined as a study on polarimetric method of magnetic field measurement. Preliminary interferometric experiments are also carried out on a compact toroidal plasma with field-reversal configuration.     

The feasibility of producing laser plasmas via photoionization

The production of uniform large-volume laser plasmas with electron-ion densities on the order of 10¹²/cm³or larger by means of photoionization is investigated. An externally applied electric field heats the electron gas to the optimal temperature for excitation of laser levels. Photoionization by intense UV light may take place in a low partial pressure gas of low ionization potential species dispersed throughout the host laser medium, or the laser medium itself may serve as the photoionized species. Both single-photon ionization and two-photon two-step ionization are shown to be applicable.     

Spectrally discriminating time-resolved and space-related X-ray plasma diagnostics

The experimental study of laser-produced plasmas, particularly those relevant to laser fusion, has long motivated the development of new X-ray plasma diagnostic techniques. This paper summarizes the application of a number of novel space-resolved and time-resolved X-ray diagnostic systems to the study of plasmas produced by the 1 beam 0.35 μm GDL facility, and by the 24 beam 1.05 μm OMEGA facility at the Laboratory for Laser Energetics. Two time-resolving X-ray spectrometers are described, one utilizing a transmission grating as a dispersive element, the other employing an array ofK-edge filters for spectral discrimination. A transmission grating is also used in conjunction with a Kirkpatrick-Baez microscope to provide spectrally dispersed high spatial resolution images of the laser-produced plasmas. The usefulness of these instruments in measuring specific plasma parameters and identifying particular spectral features, in some cases with the aid of other diagnostic instrumentation, is illustrated.     

1.06μm激光等离子体散射特性研究

利用波长为1.06μm、单脉冲能量约为500 mJ的脉冲Nd:YAG激光经焦距为300 mm的正透镜聚焦,使焦点处激光能量密度剧增而引起大气分子中的原子电离,在发生同波长激光散射和多光谱电磁辐射现象的同时,开展空间分辨光谱的探测,获得1.06μm脉冲激光经大气等离子体散射的空间分布情况。采用HR4000光谱仪对散射情况进行测量分析,通过计算机模拟计算得到等离子体对1.06μm激光散射的方向图,基于Mie理论解释了入射波长为1.06μm脉冲激光散射角与散射强度之间的关系。     

Relative strength of second harmonic and 3/2 omega emissions fromlong-scale-length laser produced plasmas

Experiments were conducted on the planar slab targets of carbon, aluminum, and copper using a 1.0641-μm laser at laser intensities varying from 2×10¹² to 1×10¹⁴ W/cm². The laser had a fluorescent linewidth of 4.5 Å. Spectral profiles of parametrically modulated second-harmonic as well as 3/2ω₀ emissions have been measured for the long-scale-length plasmas so generated. Relative strengths of these emissions with respect to peak signal intensity and spectral energy content as a function of laser intensity are graphically reported. Results are discussed on the basis of two plasmon and parametric decay instabilities     

气压对激光诱导等离子体辐射特征的影响

我们使用Ｎｄ：ＹＡＧ激光器烧蚀金属Ａｌ靶获得等离子体,在１００Ｐａ～１００ｋＰａ气压范围内,进行了环境气体压强对激光诱导等离子体辐射特征影响的研究．使用的气体是Ａｒ气,激光能量１４５ｍＪ．结果发现,最大特征辐射强度在１０ｋＰａ、靶前０．１ｍｍ处、延时１８０ｎｓ获得;而信号－背景是在靶前１．０ｍｍ处、延时４５０ｎｓ达到最大值．基于Ａｌ等离子体不同气压下的时间－空间分辨谱,对结果进行了简单的讨论．     

Dynamics of optical caviton generation in a CW-seeded frequencyshifted feedback cavity

We analyze the dynamics of soliton creation in a frequency-shifted feedback ring laser with injected continuous wave seed. We show that for an active cavity the soliton buildup time may be estimated analytically. The soliton emission from the CW-pumped laser is analogous to the generation of cavitons by the resonant absorption of laser beams in inhomogeneous plasmas. We study the dynamics of optical cavitons by means of perturbation theory and numerical simulations     

纳秒、飞秒激光脉冲下铝等离子体发射光谱及其空间特性的比较

研究了４５ ｆｓ和６ ｎｓ的强激光脉冲作用铝靶等离子体的发射光谱特性,发现在飞秒下Ｘ射线发射以Ｋ 壳层为主,等离子体的温度（５００ ｅＶ）,电子密度（３×１０２１／ｃｍ ３）比纳秒情况（１００ ｅＶ,２×１０２０／ｃｍ ３）下要高;铝等离子体的Ｘ射线发射长度短而且强区更靠近靶面。     

激光入射角对光声信号大小的影响

本文分析了高强度激光斜入射时等离子体共振吸收对光声信号的影响，导出了等离子体共振吸收最强时激光入射角的表达式，得出了激光斜入射时，随着激光入射角的增大，光声信号会出现一个极大值，并通过实验进行了验证。