基于反射型棱栅的色散系统失调及光谱剪切效应研究

As a novel component, the reflection grism can be combined with a grating or prism device for dispersion compensation in the ultra-short laser pulse system. The reflection grism pair has an advantage that it can provide large amounts of negative group delay dispersion (GDD) and negative third order dispersion (TOD), which can compensate in magnitude the positive GDD and TOD of most dispersive optical materials. In addition, the grism arrangement is easy. However, when the surfaces of grisms are not parallel, the recompressed pulse becomes distorted and contrast ratio declines. Therefore, in the case that the errors, defect and spectral loss of dispersion system are inevitable, finding the balance point of the factors and optimizing system becomes a new way to improve the quality of the compressed beam..In this project, we design a non-collinear optical parametric chirped-pulse amplification (NOPCPA) system based on the reflection grism. The phase changes and effects on the recompressed pulse due to non-parallel grisms are studied. Additionally, the spectral clipping of grism is analyzed. We also establish the contact between grism non-parallelism and spectral clipping. The model of common modulation of grism non-parallelism and spectral clipping on the output pulse is revealed. Furthermore, combining numerical simulation and experimental results, the system parameters are globally optimized and the compensation measures of dispersion errors are proposed. This project will provide foundations for the application of grism as dispersion device.

反射型棱栅作为新型色散元件，具有结构紧凑、排列简单、能同时提供负的二阶、三阶色散等优点，在补偿材料高阶色散方面具有显著优势。然而色散元件的排列误差、制造缺陷以及光谱剪切等因素，导致光谱位相畸变，压缩脉冲失真，对比度降低。在以棱栅为基础的色散控制系统失调、缺陷、光谱缺失不可避免的情况下，寻找彼此制约的平衡点，整体优化系统，成为提高压缩光束质量的新思路。. 本项目以非共线光参量啁啾脉冲放大系统为基础，反射型棱栅为研究对象，超短脉冲的时空特性为主线，系统研究棱栅的制造缺陷、调节误差产生的剩余色散，尺寸限制造成的光谱剪切效应；建立棱栅的失调、光谱剪切之间的联系，揭示其交叉调控超短脉冲的机理；利用理论和实验相结合，提出色散补偿措施，确定误差容限，整体优化系统参数。此研究为棱栅在工程中的应用奠定基础、提供理论依据。

本项目以非共线光参量啁啾脉冲放大系统为基础，反射型棱栅为研究对象，系统研究棱栅的制造缺陷、调节误差产生的剩余色散，尺寸限制造成的光谱剪切效应，揭示其交叉调控超短脉冲的机理，提出色散补偿措施，确定误差容限，整体优化系统参数。主要结果如下：棱栅存在调节误差或缺陷时，偏离角对色散影响很大，尤其是三阶色散。旋转方向仅对棱栅表面失配有影响。色散随棱栅间距线性变化，而随光栅刻线密度非线性变化。色散变化对入射角很敏感。棱栅调节存在误差时，剩余二阶色散将会导致脉冲向后沿倾斜，剩余高阶色散将导致脉冲出现尾翼。棱栅表面的失配相较于刻线的失配对脉冲的影响更甚，仅0.1度的偏差就导致脉宽显著增加，对比度恶化。棱栅或其他光学元件的有限尺寸将导致光谱剪切。允许通过的光谱带宽非对称，波长更短的光谱成分更容易被剪切。入射光谱为双曲正割型，输出脉冲的对比度最好。当棱栅尺寸和光栅常数等结构参数确定后，光束越宽，其光谱越容易被剪切。减小入射角和棱栅间距可以缓和光谱剪切。棱栅失配会加剧剩余位相，与光谱剪切共同作用，会进一步展宽脉冲，降低对比度。更高阶色散远超光谱剪切对压缩脉冲波形的作用。补偿高阶色散将改善压缩脉冲波形。棱栅的对准误差对带宽、光束尺寸、光栅刻线密度、入射角等参数非常敏感。对于较小的光栅刻线密度和脉冲宽度、较大的入射角和光束宽度，表面失配误差更严格得多。在相同结构参数情况下，棱栅刻线失配的误差容限明显更高。刻线失配时，光谱剪切对误差容限的影响很小。因此，通过调节棱栅间距、结合声光可编程色散滤波器的光谱位相控制、利用刻线失配优化表面失配等手段有利于超短脉冲系统色散优化设计，改善输出光束质量，为棱栅的实际应用提供理论依据。本项目按照计划内容完成了科研任务。依托本项目，已发表2篇SCI论文，授权1项发明专利，2篇SCI、1篇中文核心投稿、审稿中。项目成员2人晋升副教授，现有2名研究生在读。