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采用OPCPA技术提高高功率飞秒激光对比度研究
Improving the Contrast Ratio of High Power Femtosecond Laser by Using of OPCPA Technique
【作者】 马再如；
【导师】 陈建国；
【作者基本信息】 四川大学 ， 光学， 2006， 博士
【摘要】 对比度是高强度飞秒激光的重要参数之一，它是限制高强度飞秒激光在强场物理、聚变能和高次谐波产生等领域进一步应用的瓶颈。 光参量啁啾脉冲放大(OPCPA)技术结合了光参量放大(OPA)技术和啁啾脉冲放大(CPA)技术的优点，具有极高的增益系数、很宽的增益带宽、弱的热效应、高的转换效率和增益的时间选择性强等特点。采用该技术能获得高强度高对比度飞秒激光输出，但还有很多的关键技术问题需要突破。目前，采用OPCPA技术代替再生放大器是获得高对比度、高强度飞秒激光的较优选择。研究这类激光系统的对比度有很重要的现实意义。 本文分析了三阶非线性克尔效应和色散对飞秒激光的时空特性和对比度的影响。研究了运行在大增益区的OPCPA激光器的性能，分析了同步抖动对OPCPA输出飞秒脉冲的影响，以及采用长脉冲泵浦(比信号光脉冲长)的方式对输出飞秒脉冲特性的影响，在此基础上，就光直接同步方式中的关键技术——泵浦光成形技术进行了详细的理论研究，提出了采用多个超短脉冲叠加器来形成窄带、脉冲宽度可调的平顶泵浦光。主要的研究结果如下： 1、利用大啁啾信号光的频谱在时域内的分布特点，采用宽带数值计算模型，并对大增益情况下的三波耦合方程进行了详细的研究。研究结果表明，因信号光各部分的位相匹配不同，造成了系统的功率转换效率随三光波的相互作用距离而形成一种有准振荡结构，在第一个极值点为其最大的转换率；系统进入深度增益饱和状态，系统的稳定性大大优于小信号增益状态，但系统的对比
【Abstract】 The contrast ratio, defined as the peak intensity of the main pulse to the intensity of the largest pre-pulse, is a very important parameter of the high intensity femtosecond laser pulse, and which is the bottle in limiting the further using of the femtosecond laser in the fields of the high field physics, high order harmonic generation and laser fusion, etc.The optical parametric chirped pulse amplification (abbreviate to OPCPA) possesses the advantages of the optical parametric amplification (abbreviate to OPA) and the chirped pulse amplification (abbreviate to CPA) together, which includes the characters such as very high gain coefficient, broadband gain bandwidth, weakly thermal effect and high energy conversion coeffient. Adopting the OPCPA is a most potential way to archeve high intensity femtosecond with high contrast after many key techniques to be solved. Nowadays, many high femtosecond with high contrast is archieved by adopting the OPCPA to altenate the regenetive amplifier in traditional CPA lasers.Firstly, the influences of the third order nonlinear Ken effect and the dispersion originated from the mismatch of the grating pairs in the compressed stage on the contrast and the temporal-spatial domain properties of the femtosecond are researched. Secondly, the property of the OPCPA laser operation in the big gain regime is studied. Thirdly, the effects of synchronization jetter between the signal pulse and the pump pulse in the OPCPA system and its traditional solvesion, namely