复合非均匀结构Bragg器件制备及其应用研究

The pulse compression and stretching device with compact, high efficiency, large dispersion and high damage threshold is always the core device in high-power ultra-short laser technology. In this project, a novel Bragg device with composite non-uniformity structure is proposed. The application of pulse compression and stretching with large dispersion based on the Bragg device will be studied. Combining on the coupled-wave theory and F matrix, the physical model and structural design method of the Bragg device will be built. The characteristics of diffraction and dispersion will be researched. Based on the research on the photo-sensitivity and crystallization characteristics of photo-thermo-refractive glass and non-uniformity grating-writing technology, the composite non-uniformity Bragg device will be fabricated. Performance of the composite non-uniformity Bragg device will be characterized and the time-space characteristics of output laser pulse will be analyzed. The pulse compression and stretching from ns to hundreds of ps based on the composite non-uniformity Bragg device will be researched theoretically and experimentally.

具有紧凑、高效、大色散、高损伤的脉冲压缩与展宽器件一直是高功率超短脉冲激光技术的核心器件。本项目提出一种新型复合非均匀结构Bragg器件，并开展其在大色散延迟脉冲压缩与展宽方面的应用研究。结合耦合波理论和F矩阵，建立复合非均匀结构Bragg器件的物理模型和结构参数设计方法，分析其衍射特性与群色散延迟特性。研究光热敏折变玻璃的光敏和析晶特性以及非均匀光栅的写入技术，制备复合非均匀结构Bragg器件。开展复合非均匀结构Bragg器件的性能表征研究，明确器件输出的脉冲时空特性。理论与实验相结合，开展基于复合非均匀结构Bragg器件的ns级至百ps级脉冲压缩与展宽技术研究。

高能高功率的皮秒超短激光脉冲在工业加工、科学研究等领域有着广泛的需求。皮秒-百皮秒超短激光脉冲的高效放大却面临着诸多问题。啁啾Bragg体光栅损伤阈值高、色散能力强，系统结构简单紧凑，是脉冲展宽和压缩的关键器件之一。本项目结合F矩阵和经典耦合波理论，建立了啁啾Bragg体光栅的物理模型。研究了光栅光谱带宽特性、色散特性。采用平面波与柱面波干涉曝光和两步热处理法，在光热敏折变玻璃中制备了啁啾Bragg体光栅，利用超连续谱光源测量了光栅的波长选择性曲线。当光栅线对数为3650lp/mm、折射率调制幅度为103ppm时，传输矩阵方法模拟得到的波长选择性曲线与测量结果相符；提出了一种对称的级联构型，该构型具有单块光栅厚度小、消空间啁啾和“即插即用”等优点。采用1030nm皮秒光纤激光器，开展了啁啾Bragg体光栅展宽与压缩脉冲的实验研究，在一块光栅上同时实现脉冲展宽与再压缩，且再压缩脉冲脉宽与初始脉冲脉宽相等。采用两块光栅级联结构设计，将脉宽15ps的初始脉冲展宽至约1ns，与数值模拟结果相符合，整个展宽器的长度可控制在约23cm。采用能量50J、脉宽3ns、中心波长1053nm的激光器，开展了啁啾Bragg体光栅的激光损伤研究。在1-on-1测量方式下，光栅的零概率面损伤阈值约为10.3J/cm2；在R-on-1测量方式下，光栅的零概率面损伤阈值为15.2J/cm2，光栅的零概率体损伤阈值为19.1J/cm2。利用光学显微镜对样品表面损伤形貌进行了研究，发现样品后表面的能量沉积多于前表面。采用经验公式，并结合光热敏折变玻璃的色散曲线，估算得出基于光热敏折变玻璃的啁啾Bragg体光栅的非线性折射率为4.7×10-20m2/W。这些结果可为啁啾Bragg体光栅在高能高功率激光条件下的应用提供参考。本项目所取得成果可为扩展啁啾脉冲放大技术的应用研究提供参考，同时也为皮秒-百皮秒超短激光脉冲的展宽与压缩提供一种简单、紧凑的解决方案。