双束“自陷”激光驱动的电子等离子体波的拍频激发

本文提出并详细研究了应用两束“自陷”激光激发电子等离子体波(EPW)来维持等离子体拍频加速器(PBWA)中光束及其激发的EPW的会聚。文中导出了EPW饱和振幅所满足的方程,自洽地研究了泵浦光束的“自陷”条件,并解析地得到了最佳离谐条件及其对应的最佳初始等离子体密度以及EPW的最大振幅。在高斯型自陷泵浦光束情况下,文中应用数值法计算了EPW的横向分布。对于一定的离谐参量,此分布呈现出独特的性质。此外,本文还得到了由泵浦光束的非均匀性所产生的EPW电场的径向分量,并简要地讨论了它对PBWA中粒子加速的影响。 关键词：     

啁啾匹配OPCPA方案用于消除超短激光脉冲的预脉冲

采用了一种利用啁啾匹配光参量啁啾脉冲放大（OPCPA）技术来消除泵浦脉冲时间窗口内的预脉冲的方法,并对该方法展开了数值模拟研究。分析了泵浦光脉冲形状、预脉冲提前时间等因素对预脉冲消除效果以及信噪比提升情况的影响。通过与传统的非共线OPCPA方案对比,发现啁啾匹配OPCPA方案可以消除掉离主脉冲更近的预脉冲,且它对预脉冲的消除效果受泵浦光脉冲形状的影响较小。     

增益调制高重频脉冲光纤激光器实验研究

采用脉冲泵浦方案,研制出了基于增益调制技术的全光纤结构高重频脉冲激光器。采用电路直接调制的激光二极管作为泵浦源,双包层光纤作为增益介质,构造了光纤光栅选模的线形腔结构。实验中通过调整泵浦光脉冲宽度和光纤激光器谐振腔长度,得到了稳定的高重频脉冲。在100kHz重复频率下,采用21W的峰值泵浦功率和2.5μs的泵浦脉冲宽度,获得了1.06μm波长,脉冲宽度247ns的稳定脉冲激光输出。脉冲峰值功率一致性好,平均功率长期功率稳定性为2%。观察并分析了由于纵模拍频在脉冲包络上产生的次脉冲特性。通过一级放大实现89.6 W输出。     

基频和三倍频Nd:YAG激光诱导熔石英损伤特性

 采用光电探测器和数字示波器检测散射光脉冲信号,研究了基频和三倍频Nd:YAG激光诱导熔石英损伤过程,给出了泵浦光和探针光的散射光光电信号;比较了基频和三倍频激光作用下熔石英烧蚀斑显微照片,并分析了其损伤机理。结果显示:在ns脉冲激光作用下,熔石英损伤均发生在泵浦激光脉冲峰值附近,且基频光作用下损伤开始时间点比三倍频作用下早;在多脉冲或高能量激光辐照下,检测到了等离子体闪光信号,等离子体闪光发生在时间延迟21 ns附近。基于Keldysh理论计算了基频光和三倍频光作用下,熔石英光致电离速率同激光强度的关系。     

V型三能级系统中高阶非线性效应的研究

本文采用二阶相干函数理论研究了V型三能级系统中三阶及五阶极化拍频（TPBVTS及FPBVTS）的非线性效应。通过对泵浦光为宽带及窄带情形的分析，我们发现三阶及五阶极化拍频信号的强度在时域内的变化取决于激光的统计特性和跃迁的横向弛豫率，从而在测量原子能级分裂时可以得到消除多普勒极限增宽的精度，另外，我们对信号的空间调制也进行了分析。     

级联三能级系统中高阶非线性效应的研究

本文采用二阶相干函数理论研究了级联三能级系统中三阶及五阶极化拍频(TPBCTS及FPBCTS)的非线性效应.通过对泵浦光为宽带及窄带情形的分析,我们发现三阶及五阶极化拍频信号的强度在时域内的变化取决于激光的统计特性和跃迁的横向驰豫率,从而在测量原子能级分裂时可以得到消除多普勒极限增宽的精度.另外,我们对信号的空间调制也进行了分析.     

光折变晶体中二波耦合光强依赖皮秒光脉冲整形

波长为532nm、主脉冲脉宽为55ps、重复频率为82MHz的激光脉冲列在掺Ce的KNSBN晶体中进行二波耦合.当探测脉冲(倒空脉冲)相对于泵浦脉冲有一定时间延迟时,泵浦脉冲发生整形.整形效果随入射总光强的增大而变得越来越明显.实验结果与理论符合很好.     

V型三能级系统中高阶非线性效应的研究

本文采用二阶相干函数理论研究了V型三能级系统中三阶及五阶极化拍频(TPBVTS及FPBVTS)的非线性效应.通过对泵浦光为宽带及窄带情形的分析,我们发现三阶及五阶极化拍频信号的强度在时域内的变化取决于激光的统计特性和跃迁的横向弛豫率,从而在测量原子能级分裂时可以得到消除多普勒极限增宽的精度.另外,我们对信号的空间调制也进行了分析.     

声光调制器在激光腔倒空技术中的应用

本文介绍了以36°Y切铌酸锂为换能器,以熔石英为声光互作用介质,驱动频率为389。5MHz的声光调制器的设计;计算并选定了换能器的各镀层厚度,研制成了用于激光腔内的中心频率389.5MHz声光脉冲调制器;叙述了该器件在同步泵浦染料激光器腔倒空技术中的应用。实验表明,当驱动平均功率约0.2W时,用该器件所实现的激光腔倒空的倒空比约40％。     

二极管泵浦Nd:YAG激光器的脉冲间隔调制

在激光通信线路可,腔倒空Nd:YAG激光器用于产生光脉冲,用脉冲间隔调制来对数据进行编码。三组GaAs二极管连续泵浦一个端面镀有高内反射膜的Nd:YAG棒。偏振光分束器以90°角反射s偏振光,形成L形状的激光腔。根据偏振相对于所加电压的延迟,铌酸锂调制器调制传播功率。产生     

Beat-wave excitation of plasma waves based on relativistic bistability

A nonlinear beat-wave regime of plasma wave excitation is considered. Two beat-wave drivers are considered: intensity-modulated laser pulse and density-modulated (microbunched) electron beam. It is shown that a long beat-wave pulse can excite strong plasma waves in its wake even when the beat-wave frequency is detuned from the electron plasma frequency. The wake is caused by the dynamic bistability of the nonlinear plasma wave if the beat-wave amplitude exceeds the analytically calculated threshold. In the context of a microbunched beam driven plasma wakefield accelerator, this excitation regime can be applied to developing a femtosecond electron injector.     

Control of gradient-driven instabilities using shear Alfvén beat waves

A new technique for manipulation and control of gradient-driven instabilities through nonlinear interaction with Alfvén waves in a laboratory plasma is presented. A narrow, field-aligned density depletion is created in the Large Plasma Device, resulting in coherent, unstable fluctuations on the periphery of the depletion. Two independent shear Alfvén waves are launched along the depletion at separate frequencies, creating a nonlinear beat-wave response at or near the frequency of the original instability. When the beat wave has sufficient amplitude, the original unstable mode is suppressed, leaving only the beat-wave response, generally at lower amplitude.     

Robust autoresonant excitation in the plasma beat-wave accelerator

A modified version of the plasma beat-wave accelerator scheme is proposed, based on autoresonant phase locking of the Langmuir wave to the slowly chirped beat frequency of the driving lasers by passage through resonance. Peak electric fields above standard detuning limits seem readily attainable, and the plasma wave excitation is robust to large variations in plasma density or chirp rate. This scheme might be implemented in existing chirped pulse amplification or CO2 laser systems.     

Superradiant linear Raman amplification in plasma using a chirped pump pulse

A theoretical and numerical investigation of small-signal Raman backscattering from a chirped pump pulse in plasma shows that an ultrashort probe pulse will grow superradiantly, i.e., with an amplitude that scales with the propagation length while contracting self-similarly. These features are commonly associated with the nonlinear stages of Raman amplification in the pump depletion and Compton regimes. We show that the superradiant scaling results in very broad-bandwidth amplification due to gain distributed in frequency as well as spatially. Since different frequencies excite the plasma at different positions, wave breaking is avoided, and prepulses and pedestals are substantially suppressed. Linear chirped pulse amplification in plasma could provide a very broad-bandwidth alternative to solid state laser amplifiers, potentially usable for optical pulses a few cycles in duration.     

Effect of Brillouin slow light on distributed Brillouin fiber sensors

The effect of Brillouin slow light on distributed Brillouin fiber sensors (DBFSs) is studied. We demonstrate Brillouin slow light for a 1.2 ns pulse with peak powers (PS) from 3.3 to 56.2 mW on depletion of the pump power (PP) ranging from 1.3 to 83.2 mW in conventional optical fibers (SMF-28). Experiments show that, when pump power depletion is not negligible, for a given PP the Brillouin gain and delay time of a pulse decrease when PS increases in a long (> or =10 km) sensing fiber. The optimum pump beam depletion resulting from strong interaction of the pump and the probe in the fiber provides accurate temperature and strain information at a high spatial resolution. Our study reveals that at low PP the spatial resolution error caused by the pulse delay for a DBFS with centimeter spatial resolution is less than 5% of the pulse length.     

等离子体拍频波加速器中三波相互作用的时间发展

计算了等离子体拍频波加速器中双频抽运光与Langmuir波的相互作用及其时间发展。指出Langmuir波出生成到饱和的过程,与三波位相由匹配到失配密切相关。三波位相差作为描写三波耦合程度的量对于双频激光激发Langmuir波至关重要。 关键词：     

Transformation of a nonlinear plasma wave into electromagnetic radiation in a periodic magnetic field

We study transformation of a nonlinear plasma wave into electromagnetic radiation in the periodic static magnetic field of an undulator. Such a wave can be excited by a short laser pulse or a relativistic electron bunch. The features of relativistic upper-hybrid plasma oscillations are analyzed. In the approximation of constant pump, resonance conditions of excitation of an electromagnetic wave and the characteristic transformation length are found. The nonlinear stage of transformation with allowance for pump depletion is considered. The studied phenomenon can be used for development of a high-power terahertz-radiatoin source. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 6, pp. 496–507, June 2007.     

啁啾脉冲受激布里渊散射的理论研究

推导了描述调频激光受激布里渊散射的耦合波方程和准静态近似下增益因子的表达式，分析了啁啾脉冲的散射过程，讨论了泵浦激光和斯托克斯信号光率调制方式，带宽对泵浦光能量抽取效率和斯托克斯光脉冲波形的影响。     

Backward Raman amplification in a plasma waveguide

Backward Raman amplification of a short laser pulse in a plasma waveguide is demonstrated. With a guided seed pulse of 0.8-microJ energy and a pump pulse of 345-mJ energy in a 9-mm-long optically preformed plasma waveguide, 910-fold energy amplification is achieved. Heating of the plasma by the long pump pulse is identified to be a key issue for plasma-waveguide-based backward Raman amplifiers.     

High density plasmas for recombination X-ray lasers

The scaling of recombination XUV lasers to shorter wavelengths requires laser plasmas produced at initial electron densities close to solid. With pump laser pulses longer than a few tens of picoseconds the hydrodynamic motion of the plasma during the interaction makes this difficult to achieve. In contrast, when picosecond laser pulses are used the laser energy is absorbed close to solid density since the plasma expansion is insignificant during the laser pulse. This results in hot near solid density plasmas which are needed for hydrogenic recombination X-ray lasers operating in the water window. Experimental observations have shown that a fully ionized aluminium plasma with a temperature of about 400 eV and a density well above 10²³ cm^–3 is produced when an aluminium target is irradiated with a single 3.5 ps high power KrF laser pulse.