基于切趾啁啾Bragg体光栅的高峰值功率脉冲压缩与展宽研究

Compact pulse stretcher and compressor with high efficiency and high damage threshold is the key to the development of high energy and peak power lasers. Chirped volume Bragg gratings (CVBGs) is a new type of stretcher and compressor and become the research hotspots at present. However, the high frequency and small amplitude oscillation in linear group delays, caused by the high-order dispersion is the bottleneck problem for development of CVBGs. In this foundation, the apodization method is proposed to suppress the high-order dispersion and optimize the diffraction characteristics of CVBGs, which can improve the time and frequency domain quality of output pluses. The coupled wave theory and matrix analysis method which is optimized by loss characteristics and non-linear refractive index coefficients is used to set up the mathematical model and design method of apodized chirped volume Bragg gratings (ACVBGs) for high energy and peak power lasers. The new methods and Technologies of nanofabrication will be explored, and new manufacturing Technology of apodized chirped volume Bragg gratings will be revealed. Combining the high energy and peak power laser system in the Laser Fusion Research Center of China Academy Of Engineering Physics, The pulse stretching and compression based on apodized chirped volume Bragg gratings will be studied in theoretical and experimental. The pulse characteristics of time domain, space domain and frequency domain in different process of stretching, amplifying and compressing will be analyzed, and the demonstration experiment will be completed. This foundation will undoubtedly open up the cross-application fields of structural functional optical elements and advanced laser technology, and expect to provide core elements and technical reserves for the development of peak and peak power lasers. These researches can provide technical support for frontier science, national defense and industry.

紧凑型脉冲压缩与展宽是高能高峰值功率超短脉冲激光发展的方向之一。啁啾Bragg光栅作为一种展宽与压缩器，其高阶色散引起的线性群延时中存在高频、小幅振荡一直是人们关注的问题。本项目提出一种新型切趾啁啾Bragg体光栅，用于抑制高阶色散，提升光栅衍射特性和输出脉冲时空特性；综合材料的损耗特性和非线性折射率系数，建立面向高能高峰值功率超短脉冲激光的切趾啁啾Bragg体光栅物理模型；开展切趾啁啾Bragg体光栅的制备技术与工艺研究；结合中物院激光聚变研究中心的激光系统，开展基于新器件的脉冲压缩与展宽研究，分析脉冲在展宽、放大、压缩各环节的时域、空域、频域特性，完成实验论证。本项目无疑将开拓结构功能光学器件和先进激光技术交叉应用的研究领域，有望为高峰高峰值功率激光发展提供核心器件与技术储备，为前沿科学、国防以及工业等领域的科技进步提供技术支持。

啁啾Bragg光栅作为一种展宽与压缩器，其高阶色散引起的线性群延时中存在高频、小幅振荡一直是人们关注的问题。本项目提出一种新型切趾啁啾Bragg体光栅，用于抑制高阶色散，提升光栅衍射特性和输出脉冲时空特性；综合材料的损耗特性和非线性折射率系数，建立面向高能高峰值功率超短脉冲激光的切趾啁啾Bragg体光栅物理模型；开展切趾啁啾Bragg体光栅的制备技术与工艺研究。取得的主要结果如下：①深入开展了切趾啁啾Bragg光栅的设计技术研究。啁啾Bragg光栅群延时中的振荡周期随波长增加而增加，振荡幅度随折射率调制度增加而增加；明确了啁啾Bragg光栅群延时振荡主要源自光栅入射面处反射光与光栅内衍射光之间的干涉；提出采用半边余弦切趾可有效地抑制啁啾Bragg光栅的群延时振荡，但会降低频谱响应带宽。②持续开展了切趾啁啾Bragg光栅的制备技术研究。分析了不同核化温度下自由能Ag晶核半径的关系，通过控制曝光剂量、降低核化温度、延长核化时间，获得了高浓度、小半径的NaF析晶。③开展了切趾啁啾Bragg光栅的脉冲展宽与再压缩实验研究。利用两块啁啾Bragg光栅实现了脉冲展宽与再压缩，且再压缩脉冲脉宽与初始脉冲脉宽相等；但由于啁啾Bragg光栅24%的损耗影响，压缩脉冲的频谱强度约为-50dBm。④探索了啁啾Bragg光栅的非线性特性。结合经验公式和光热敏折变玻璃的色散曲线，预估了啁啾Bragg光栅的非线性折射率；分析了三种配方的光热敏微晶玻璃各组分折射度分布，为后续降低光栅非线性折射率提供了指导。⑤提出了基于啁啾Bragg光栅的脉冲时间合成技术。分析了实现脉冲串时间合成的物理机制，分析了合成效率与光栅参数之间的关系，研究了不同脉宽的脉冲串实现高效脉冲时间合成的光栅参数设定。这些结果可为啁啾Bragg光栅在高能高功率激光条件下的应用提供参考。