基于光参量放大的高平均、高峰值功率 8-14µm宽调谐激光产生研究

8-14μm spectrum is an important atmospheric window located in far-infrared region. It has low atmospheric loss and strong permeability in severe environment, covers the characteristic thermal spectrums of object with temperature ranging from -66 to 90 degrees Celsius, and locates in the molecular fingerprint region of materials. Coherent tunable powerful source in this region has significant applications in atmospheric laser remote sensing and communication, national security and high resolution Molecular spectroscopy. Parametric frequency down-conversion of the well developed 1μm solid-state laser based on nonlinear crystal has been proved to be an effective way to obtain the 8-14μm tunable laser with practical and precise characteristics. This project will investigate the basic science problems related to frequency conversion from 1μm to 8-14μm range and achieve tunable 8-14μm laser with high average and high peak power based on optical parametric amplification by optimizing the nonlinear infrared crystal for the first time. Implementation of this project will help to push forward the development of high power 8-14μm laser with practical and precise characteristics in China, and promote the development and innovation of related fields of application.

8-14μm属于长波红外波段,是一个极其重要的大气窗口,具有极低的大气损耗和高的恶劣环境穿透能力,覆盖了温度-66℃至90℃物体的红外特征谱，并处于物质的分子指纹区，因此该波段强相干辐射源在大气遥感与通信、国家安全及高分辨分子光谱学等诸多领域具有重大的应用价值。基于非线性晶体光参量效应将成熟的1μm固体激光频率下转换是发展实用化与精密化8-14μm激光源的最有效手段之一。本项目首次基于高效光参量放大，通过优选非线性红外晶体，系统开展1μm激光向8-14μm激光频率下转换的基础科学问题研究，实现高平均、高峰值功率8-14μm宽调谐激光产生。本项目的开展有助于推动我国高功率实用化精密化8-14μm激光源向前发展，并促进相关应用领域的进步与创新。

针对8-14μm相干辐射在大气激光遥感与通信、国家安全及高分辨分子光谱学等诸多领域的重大应用需求，本项目开展了1μm固体激光向8-14μm激光频率下转换的基础科学问题研究，取得了重要研究成果：.1)建立了国内唯一超宽调谐中红外光参量激光表征评估实验及数值仿真平台。实验平台基于成熟1μm激光泵浦光参量放大器（OPA），可评估红外晶体2-20μm光参量激光产生性能，并对晶体基本变频参数实验修正，特别是对尺寸小、光学质量差及基本参数欠缺的新晶体具有重要价值。数值仿真基于三波耦合方程，光束空间及时间分布均采用高斯近似，考虑了泵浦光损耗、参量光空间走离、参量光脉冲时间走离（GVM）与色散（GVD）、晶体线性吸收等因素，可给出OPA变频效率、输出光的功率/能量、脉冲波形、光强空间分布和光束质量等重要参数，用于优化调控泵浦参数及晶体长度，指导及预测实验；.2)进行了皮秒OPA长波红外8-14µm激光产生理论与实验研究。基于近年来发展的新型非线性红外BaGa4Se7（BGSe）晶体，首次将1μm Nd:YAG激光直接频率下转换，实现了波长连续调谐皮秒8-14μm大能量光参量激光输出，8-14μm波段输出单脉冲能量范围140-230μJ，属当前国际最高水平；.3)进行了新型宽带隙红外晶体BaGa4S7 （BGS）中红外激光输出特性表征评估。首次实现了BGS晶体基于1μm激光泵浦的皮秒超快6.3-8.8μm光参量激光连续调谐输出，为BGS晶体国内首次实现中红外激光输出；.4)研制出了国内首台8-14μm连续调谐长波红外光参量激光放大器实验室样机，兼具实用化与精密化特性，对于研究红外探测器与长波红外激光的作用机理及效应具有重要意义。. 本项目在一定程度上推动了我国新型红外晶体材料及实用化精密化8-14μm激光源的发展，同时促进了相关应用领域的进步与创新。