双波长激光同步辐照下DKDP晶体体损伤机制的瞬态吸收研究

High power laser induced damage (LID) in bulk DKDP crystals is becoming a limiting factor for the further promotion of tripling laser fluence and crystal life in high power large-aperture laser systems. LID in bulk DKDP crystal is a complex physical process. However, its LID characteristics, including small size, ultra fast speed and disorder distribution, make it difficult for using ordinary research methods to diagnose and identify the transient process and inner physical mechanism. In response to this problem, this project is going to focus on the DKDP crystal as the research object. A temporal-spatial-resolved microscopy shadowgraph technique, based on an all-optical chirped-pulse-based single-shot multi-frame imaging, will be utilized to capture the ps-μm-resolved transient multiple images during the LID in bulk DKDP crystal under the dual-wavelength nanosecond pulsed laser irradiation, and to obtain the time range of LID induction phase and the transient absorption intensity distribution images as well as discrete transient absorption spectroscopy-time curve. We propose to clarify the effect of parameter changes of synchronous conditioning laser on the run-away transient absorption and the absorption relaxation processes during the LID induction phase in bulk DKDP crystal, and to deeply understand the energy absorption kinetics and physical mechanism of LID in DKDP crystals under high power laser irradiation. The research findings of this project will not only provide scientific data support for understanding the effect of localized energy deposition of absorptive defects on LID, but also enrich LID mechanism in DKDP crystals.

强激光辐照下DKDP晶体的体损伤问题严重制约了大型高功率激光装置的三倍频激光输出通量和晶体使用寿命。DKDP晶体的激光辐照体损伤是一个复杂的物理过程，而其损伤的尺度极小、过程超快和分布无序的特点，使得常规研究手段难以识别和诊断其体损伤的瞬态过程和物理机制。针对该问题，本项目以DKDP晶体为研究对象，利用啁啾脉冲全光超快单发多幅时空分辨显微成像技术，捕获晶体在双波长纳秒脉冲激光同步辐照下，皮秒-微米时空分辨的体损伤瞬态图像，获得体损伤诱发阶段的时间范围及瞬态吸收强度分布图像和离散瞬态吸收光谱-时间曲线；阐明同步辐照预处理激光参量对晶体体损伤诱发阶段的瞬态吸收失控及吸收弛豫的影响规律，深刻理解DKDP晶体在强激光辐照下能量吸收动力学过程及损伤物理机制。本项目研究结果将为理解吸收缺陷的局域能量沉积对损伤的作用机制提供科学数据支撑，也为丰富DKDP晶体激光诱导损伤机理做出贡献。

强激光辐照下DKDP晶体的体损伤问题严重制约了大型高功率激光装置的三倍频激光输出通量和晶体使用寿命。DKDP晶体的激光损伤具有损伤尺度极小、过程超快和分布无序的特点，使得常规研究手段难以识别和诊断其体损伤的瞬态过程和物理机制。因此，本课题以DKDP晶体为研究对象，利用纳秒泵浦-超快激光探测的超快泵浦探测技术，研究了DKDP晶体在单波长和双波长激光辐照下的损伤发展及瞬态吸收的特征及演化规律，以此发展了一种可以实时探测DKDP晶体在激光预处理及损伤过程的瞬态吸收诊断方法。研究工作的开展，基本上按照项目的研究计划进行，对实验方案进行了局部调整，完成了项目的研究内容和研究目标。主要取得了以下两方面的研究成果：（1）基于纳秒泵浦-皮秒探测的瞬态阴影成像技术，获得了DKDP晶体损伤爆发过程的皮秒-微米时空分辨的损伤区扩展、喷溅及冲击波传输的动态图像和物理过程时间尺度特征；（2）基于时间拉伸色散傅里叶变换（DFT）技术的实时光谱瞬态吸收测试方法，获得了DKDP晶体激光辐照诱导过程的瞬态吸收随时间演化规律，分析了单波长及双波长辐照下晶体吸收的发展趋势，发现了双波长辐照可以使DKDP晶体更加快速趋于吸收的稳态区，结果表明355/532nm双波长辐照是一种效率更高的激光预处理方案。. 相关研究成果发表在高能量密度科学技术、Optics Express、Photonics、Matter and Radiation at Extremes等期刊文章5篇，同时获批了专利6项，参加了1次国内学术会议，培养了博士研究生1名以及联合培养硕士研究生1名。