用激光脉冲列开发小型软X射线激光

1．前言X射线显微镜、X射线光刻等各种实际应用所期待的X射线激光的开发研究正在世界范围内进行。特别是利用固体靶在1kJ以下的照射能量，证实了能产生强的放大自发辐射（ASE），各国集中力量开展用电子碰撞激发机制的类氖Ge离子X射线研究。以确认增益饱和为目的的各种实验成果已有报道。日本理化研究所提出的用激光脉冲列激发X射线激光的方案，已由劳伦斯·里弗莫尔实验室和大皈大学所验证，确认了等离子体逐次有效的加热作用，公认为是一种有效的激发手段。但是，用这种方法产生类氖Ge离子X射线激光（波长19．6nm，23．6nm）也需要几…     

毛细管放电X射线激光研究进展

近年来,毛细管放电X射线激光研究工作十分活跃,为短波长激光的研究带来一种全新的概念。较为详尽地总结了这一领域所取得的主要进展,并说明今后发展要注意的问题。对电子碰撞机制毛细管放电X射线激光研究具有一定参考价值。     

自由电子抽运X射线激光的理论探讨

X射线激光是激光物理与等离子物理中的一个重要研究领域。目前，X射线激光研究多采用毛细管放电、高功率激光的多脉冲和短脉冲等抽运方式，而且绝大多数研究局限于软X射线波段。借鉴自由电子激光器的组成结构，提出一种产生X射线激光的新方案：用钨制成毛细管的空心电极取代自由电子激光器内的摇摆器，内充特定金属蒸气，如铜蒸气之类，使自由电子激光器变成自由电子抽运X射线激光器。运用电子碰撞电离、强流粒子束平衡体系理论方程与等离子复合特性等理论对这种新型X射线激光器的工作原理及其方案的可行性作了进一步的理论分析与探讨。     

毛细管放电X射线激光研究进展

近年来,毛细管放电X射线激光研究工作十分活跃,为短波长激光的研究带来一种全新的概念。较为详尽的总结了这一领域所取得的主要进展,并说明今后发展要注意的问题。对电子碰撞机制毛细管放电X射线激光研究具有一定的参考价值。     

光场感生电离X射线激光

从理论和实验两个方面对近年来被认为很有希望实现台上X射线激光的新的泵浦机制-基于光场感生电离的复合机制和电子碰撞机制所取得的进展作了较为详尽的总结,对进一步开展X射线激光,特别是基于光场感生电离的X射线激光的研究具有一定的参考价值.     

在高度饱和桌面毛细管放电放大器中以4Hz重复率产生毫焦耳级软X射线激光脉冲

软 X射线激光有别于其它相干软 X射线辐射源的特性是其产生高能脉冲的潜力。由大型光学激光抽运的软 X射线激光输出能量已达几个毫焦耳。然而产生这些软 X射线激光脉冲的激光装置很大 ,而且它们的重复率限于几分钟一次或更少。前几年在研制以较高重复率运转的桌面软 X射线放大器方面已取得重要进展 [1 ]。在最近的工作中已演示用非常紧凑的桌面器件以 4Hz重复率产生毫焦耳量级的软 X射线激光脉冲[2 ] 。该结果在长 34 .5 cm毛细管放电等离子体柱中激发类氖氩电子在 46 .9nm波长上获得。这样的放大长度允许其增益长度乘积比获增益饱和所需…     

X射线激光的新进展

自１９８４年首次实现软Ｘ射线放大以来，已经过去１０多年。在此期间，软Ｘ射线激光取得突出进展。为使软Ｘ射线激光成为实验室工具，对它进行了广泛研究，本文回顾了在多种研究途径中所作的努力和所取得的进展。采用高强度超短激光的光电场感生电离法是很有希望的一种。本文讨论了两种软Ｘ射线激光，它们分别基于光电场感生电离后产生的复合和电子碰撞激发。     

以钕激光激发脉冲氙气流为基础的无碎片软X射线源

由纳秒脉冲激光激发脉冲氙气流（气云），获得“清洁”（无碎片）脉冲软X射线源。用X射线多层聚焦镜得到18nm的射线像。用宽带非周期多层镜和大孔径透射光栅的消像散光谱仪，记录了射线源12.5-25mm区的光谱。借助绝对校准的高速X射线电二极管AXUV－5确定了软X射线产额。     

薄膜应力测量方法研究

总结了薄膜应力的一些测量方法。将经常使用的方法归纳为激光宏观变形分析法和X射线分析法。介绍了利用测量基片弯曲曲率的激光宏观变形分析法(包括激光干涉法和激光束偏转法)和品格变形的X射线衍射法等测量薄膜应力的理论依据及其测量原理,计算了各种测量方法的测量精度,X射线分析法的精度最高,其次是激光干涉法,而激光束偏转法的精度最低,分析了激光分析法和X射线分析法的优缺点。     

靶的原子成分对飞秒激光等离子体非相干硬X射线的影响

提高飞秒稠密激光等离子体硬 X射线产额方面的研究对于高时间分辨 X射线光谱学、稠密等离子体低核能级的激发和非线性 X射线光学必需的非相干 X射线超短脉冲振荡是有意义的。靶面激光特性 (强度、脉宽和衬比度 )的最佳化和靶材原子序数的最佳选择都可提高X射线振荡的效率。激光辐射转化为软 X射线辐射 (量子能1 .2 ke V以下 )与靶物质原子序数 Z关系的研究已有报道。业已查明 ,软 X射线脉宽与靶类型关系不大 ,约为 4～ 6 ps。 0 .8～ 1 .2ke V范围等离子体的发光度也与靶类型关系不大 ,但是 2 0 0～ 30 0 e V范围内的能量转换效率却有 …     

毛细管放电软X射线激光研究进展

近几年来实用型、台式软X射线激光器发展非常迅速，特别是毛细管放电抽运的X射线激光源，已经获得46.9nm近1mJ激光输出，重复率4Hz。该台式激光器在等离子体诊断、物质烧熔等方面已经开展了初步的应用实验。本文首先简介了利用毛细管放电抽运X射线激光器的两种物理机制：电子碰撞机制和三体复合机制。然后着重介绍毛细管放电碰撞机制软X射线激光的研究进展，包括实验方案、实验装置、增益测量实验及初步的应用。对毛细管放电软X射线激光的几个关键性问题进行了讨论。     

类镍钽离子碰撞激发机制理论研究

对类Ni-Ta离子电子碰撞激发机制产生4d→4p跃迁三条激光线的增益与反转进行了探讨.首先研究了类Ni离子基态与类Co离子基态对这三条激光线上、下能级的激发与复合贡献因子及由激发产生的反转率和由复合产生的反转率;讨论了类Ni离子与类Cu离子电离速率对类Ni离子布居弛豫时间和布居大小的影响.研究结果表明,考虑光子捕获效应及激光折射效应后,4.483 nm激光线的最佳增益区域在Te≈1～1.5 keV,Ne≈(1～4)×1021 cm-3.     

Quantum efficiency of flourescence excited by photodissociation in metal halide vapors and applications

Interaction of ultraviolet radiation with diatomic and triatomic metal halide vapors is discussed. Patterns observed in ultraviolet absorption cross sections are noted. Measurements of quantum efficiency of fluorescence excited by photodissociation (QE = fluorescence photons out/ultraviolet photons in) are described. Results and their implications for 205 ± 15-nm deuterium, 213.9-nm-Zn resonance and deuterium VUV excitation are discussed. Applications of photodissociation in photodissociation lasers, electric discharge lamps, and collisional processes such as measurement of reactive and quenching cross sections are summarized.     

Short-wavelength lasers

The development of short-wavelength lasers is reviewed. Three pumping mechanisms have been demonstrated which produce lasing at wavelengths from 3 to 100 nm. These mechanisms include electron-collisional excitation, electron-ion recombination, and photo-excitation. Examples of X-ray lasers and future directions of the field are discussed     

Transient multimode dynamics in nearly single-mode lasers

The transient dynamics of nearly single-mode semiconductor lasers is studied analytically and numerically for lasers biased below threshold. The side-mode excitation probability is evaluated by solving a Fokker-Planck equation approximately. The validity of the approximate solution is verified through Monte Carlo simulations of the corresponding Langevin equations. The results show the relevance of the carrier-density overshoot during laser turn-on in determining the side-mode excitation probability. They also indicate the dependence of this probability on various device parameters such as the gain margin between the main and side modes. The experiments performed by using distributed feedback (DFB) semiconductor lasers show qualitative agreement with theory     

Large-signal dynamic model of the DFB laser

A computer model is proposed to analyze the characteristics of distributed feedback (DFB) lasers. The model is based on time-dependent coupled wave equations, with spontaneous emission taken into account. In order to avoid uncertain phase factors in spontaneous emission, a method of converting field equations to power equations in a matrix format before computation is introduced. The steady-state LI curve and transient response to the pulse excitation are calculated in the λ/4 phase-shifted DFB lasers. The longitudinal variations of the carrier and photon densities as well as of the refractive index are considered in the model     

Transient response of ARROW VCSELs

The transient response of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) is analyzed. It is found that under current modulation, the radiation loss of the transverse-leaky mode decreases during the state of the lasers but increases during the state. Numerical analysis shows that this variation in radiation loss is due to the carrier-induced refractive-index depression that arises from spatial-hole-burning of carrier concentration. It is noted that the increment in radiation loss during the state can be used to prevent net modal gain of the transverse-leaky mode from reacquiring threshold after turn-off. Hence, a new method to design ARROW, based on the variation in radiation loss, is proposed to eliminate the excitation of secondary pulsation in VCSELs. The influence of thermal lensing effects on the excitation of secondary pulsation during the state of the lasers is also investigated.     

Dynamics of longitudinal and transverse modes along the junction plane in GaAlAs stripe lasers

Observations of the transient excitation of higher order transverse modes along the junction plane in DH GaAlAs stripe lasers during subnanosecond pulse modulation is reported. These modes are strongly excited at the onset of the light pulse, they decay during 200 ps, and reappear after 400-600 ps. The width of the longitudinal mode spectrum decays from 40 to 10 Å during 0.5-1 ns.     

Transient effects in external cavity semiconductor lasers

In several important applications of external cavity operated semiconductor lasers, including studies for FM optical communication and frequency stabilized lasers for coherent communication systems, the transient response of the laser is of crucial importance. In this letter, we present a first study of the transient optical response following a step current excitation applied to an AlGaAs laser operating in a dispersive external cavity. The study shows for the first time that, for optical feedback near the gain peak of the laser, a steady state is reached after only three roundtrips in the external cavity. However, for optical feedback far (∼100 Å) from the gain peak, 20 or more roundtrips are required before a steady state can be reached. It is also shown that under certain operation conditions the optical feedback can induce damped relaxation oscillations at each subsequent roundtrip in the external cavity.