本文采用共线和非共线两种大动态范围扫描三阶相关技术测量飞秒激光脉冲，并对其测量结果及其特征进行了理论和实验分析。实验发现，共线式扫描三阶相关方法由于存在基频光在空气中通过三倍频过程直接产生三次谐波的现象，导致实际能够测量的动态范围下降；而非共线式扫描三阶相关技术虽然对脉冲强度具有较高的动态测量范围，但非共线夹角和光斑的大小对测量脉冲宽度有很大的影响。理论计算和实验结果表明，非共线情况下，入射到和频晶体上的光束夹角和光斑直径越大，测量得到的脉冲宽度也越大。共线和非共线两种方式均不影响对次脉冲位置的判断，但由于非共线式三阶相关测量得到的脉冲宽度增加，主脉冲附近的小脉冲结构或者距离较近的两个脉冲将会难以分辨。

研究了用于提高激光脉冲对比度的全光纤结构脉冲清洁器(OPC)。对利用非线性偏振旋转效应(NPR)提高脉冲对比度进行了理论分析。计算了脉冲清洁器对主脉冲峰值透射率与入射角度和光纤长度的关系,模拟了输出脉冲波形和脉宽的变化,并对1053 nm波长的百皮秒入射脉冲进行了实验。主脉冲与连续背景噪声的对比度提高47.5 dB以上,主脉冲与预脉冲对比度提高16.94 dB以上,输出信号的连续背景功率和预脉冲强度均低于探测器的最小响应极限。主脉冲的峰值功率透射率达28.05%;脉冲宽度由92 ps压缩至64 ps,与理论预期相符。利用可变衰减加光电转化的方法测量了1 Hz重复频率的脉冲对比度及信号透射率,解决了利用自相关仪不易测量低重复频率信号的问题。采用灵敏度更高的测量方式将测得更高的对比度提升。

在超强超短激光脉冲与物质相互作用过程中, 良好的激光脉冲对比度是一个非常重要的参数指标。为了扩大对超短激光脉冲对比度的测量范围, 准确地测量超短激光脉冲的对比度, 利用非线性晶体对激光脉冲强度变化十分敏感的特性, 研究了超短激光脉冲三阶相关信号的产生过程, 并在此基础上, 研制了一台三阶相关仪, 对一台飞秒激光振荡器进行了脉冲对比度的测量研究。测量结果表明, 通过在测量光路中加入聚焦透镜进行聚焦准直, 可以有效提高激光脉冲的倍频效率, 从而大幅提高该三阶相关仪的可测动态范围。该测量系统目前可实现的可测动态范围达到约108。

The stretcher system is an important part in the high-engery petawatt laser facility. The stretcher system design has a direct impact on the quality of the output pulses. The stretcher systems in some famous high-energy petawatt laser facility are summarized. And the structure and parameters are compared and discussed.

The impact of the stretcher on the contrast ratio of the out pulse is analyzed making use of the ray -tracing method , which is based on the contrast ratio model of chirped pulse.When the beam size in the stretcher is increased from 2 mm to 40 mm ,the contrast of the output pulse approximately increase two magnitude. When the input pulse is Sech2 ,the contrast of the output pulse is better than what the input pulse is Gassian or Rectangular.

In the design of the Offner stretcher, it is very important to investigate the mirror curvature radius errors, which has a direct impact on the quality of the output pulse. So it is necessary to analyse the effect on the output pulse contrast due to the mirror curvature radius manufacture errors in the ffner stretcher. A ray-tracing model for ffner stretcher with these errors is established. Based on the model, effects on output pulse contrast through the stretcher is analyzed.When the mirror curvature radius error is between 0.2%～0.5%, it can fully meet the requirements for the SHENGUANG Ⅱ petawatt laser facility. Also, when there is error for the mirror curvature radius, keeping the distance between concave mirror and convex mirror half of curvature radius of the concave mirror is better than keeping the two curve mirrors in the same center.

In a stretcher,it is important of spectral clipping. It has a direct impact on the quality of the output pulse. Base on the ray-tracing,an analytical spectral clipping model is present in the ffner stretcher . When the stretcher parameters is determined, the location of the grating placed has a very important influence on the pulse spectral clipping. When the grating placed on the symmetric center about optical axis, the spectral distribution through stretcher will be asymmetric about center wavelength of the laser, that is to say,the spectral clipping will be asymmetric spectral clipping.Therefore,the output pulse contrast will be droped approximately one magnitude in the SGII ninth beam petawatt upgrade laser facility. In order to keeping the spectral symmetry distribution about center wavelength of the laser through the stretcher, the grating must be placed on the asymmetrical position about optical axis.

Offner展宽器的设计研究中,对曲面镜曲率半径的误差研究非常重要,它直接影响输出脉冲的质量。因此有必要分析ffner展宽器中曲面镜曲率半径的误差对输出脉冲对比度的影响。参考ffner展宽器的光线追迹模型,建立了ffner展宽器中曲面镜曲率半径存在误差时的光线追迹模型; 根据建立的模型,详细分析了曲面镜曲率半径的误差对输出脉冲质量的影响; 发现在目前曲面镜曲率半径的加工误差在0.2%～0.5%的情况下,完全可以满足神光II拍瓦激光装置中对展宽器的要求; 同时发现如果曲面镜曲率半径存在误差时,应该尽量使两曲面镜之间的距离保持为凹面反射镜曲率半径的一半,而不是使两曲面镜保持同心。

在展宽器中,光谱的剪切情况非常重要,它直接影响输出脉冲的质量。以ffner展宽器为例,参照以往建立的光线追迹模型,建立了分析展宽器中光谱剪切的模型。发现当展宽器的参数确定好后,光栅放置的位置对激光脉冲光谱剪切有非常重要的影响。当光栅相对于光轴中心对称放置时,展宽器容许通过的光谱相对于激光中心波长将是非对称分布的,即此时在展宽器中发生的光谱剪切为非对称光谱剪切,在神光II第9路拍瓦激光装置中,这种非对称光谱剪切将使输出脉冲对比度下降一个数量级。为了使展宽器中通过的光谱相对于激光中心波长对称分布,需要将光栅相对于光轴非中心对称放置。

根据分析啁啾脉冲对比度模型,通过光线追迹法详细分析了展宽器对输出脉冲对比度的影响.发现当扩大进入展宽器的入射光束口径,从2 mm扩大到40 mm时,输出脉冲的对比度提高了近两个数量级;同时发现在相同条件下,当输入脉冲为双曲正割函数时,其输出脉冲的对比度明显好于输入脉冲为高斯脉冲和矩形脉冲的情形.