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题名	I类KDP和II类DKDP晶体激光损伤机理及激光预处理特性研究
作者	王岳亮
文献子类	博士
导师	邵建达，赵元安
关键词	I类KDP晶体 I-type KDP crystals II类DKDP晶体 II-type DKDP crystals 散射缺陷 ,scattering defects 非线性吸收 nonlinear absorption 激光预处理 laser conditioning
其他题名	Laser damage mechanisms and laser conditioning properties in I-type KDP and II-type DKDP crystals
英文摘要	KDP/DKDP晶体一直是人们最常用的一种电光晶体材料，且是唯一适用于当今高功率激光驱动惯性约束聚变装置中所使用的高通量激光负载材料；但倍频用的I类KDP晶体和混频用的II类DKDP晶体的激光损伤问题严重制约着高功率激光系统通量的提升。晶体生长过程中引入缺陷的特性是影响晶体损伤的关键因素，激光预处理技术也是提升晶体抗损伤性能的重要途径。本文围绕I类KDP和II类DKDP晶体在纳秒激光作用下激光损伤机理和激光预处理特性进行研究。具体开展了以下几方面的研究： 实验研究了激光诱导不同尺度散射缺陷的热学响应特性，并结合模型分析，反演了影响晶体激光损伤的缺陷特性，估算了缺陷的尺寸和吸收特性参数；明确了微米尺度/亚微米尺度散射缺陷分别是低/中等通量损伤诱导源，进而对生长工艺优化提供指导。 结合KDP晶体生长工艺控制，通过巧妙设计实验方案研究了KDP晶体材料激光损伤的缺陷尺度效应，发现I类KDP材料的1ω激光损伤阈值随缺陷尺寸减小而增加；基于线性吸收热扩散模型对实验结果反演验证了I类KDP材料中缺陷诱导激光损伤的尺寸效应，确认了I类KDP材料的1ω激光损伤机理为吸收缺陷的热吸收，并进一步明确了影响I类KDP晶体基频抗损伤性能的缺陷尺寸范围，为KDP晶体的连续过滤生长工艺优化控制，从而提升晶体抗损伤性能提供了关键参数指导和理论依据。 实验研究了II类DKDP晶体的3ω激光损伤特性，3ω激光预辐照可降低II类DKDP晶体吸收，并在一定程度内提高晶体材料的抗激光损伤能力；实验研究了II类DKDP晶体的带隙和非线性吸收特性，确定了II类DKDP晶体存在缺陷能级，缺陷能级诱导的多光子吸收过程可能是决定II类DKDP晶体高通量激光损伤的关键过程；同时发现缺陷能级可被激光强度调控，这构成了II类DKDP晶体激光预处理技术方案的理论基础，并且也得到了实验验证。 开展I类KDP和II类DKDP晶体的激光预处理技术和工艺研究，基于激光损伤机理认识，确定了I类KDP晶体采用3ω激光预处理、II类DKDP晶体采用亚纳秒激光预处理的方案；并基于抑制晶体体内广泛分布的缺陷，提出并验证了“亚纳秒+纳秒”激光预处理等优化处理方案可进一步提升晶体抗损伤性能。; KDP/DKDP crystals are widely used nonlinear optical materials that uniquely suitable for use in frequency conversion for inertial confinement fusion driver high-energy large-aperture laser systems. However, laser induced bulk damage in doubler (I-type KDP) and triplers (II-type DKDP) represents a key limiting factor in laser output expangding. Localized damage initiation in KDP/DKDP crystals has been attributed to defects that formed during growth. Laser conditioning is comfired as an effective approach to increase the LIDTs. Therefore, this dissertation researches on laser damage mechanisms and laser conditioning properties in I-type KDP and II-type DKDP crystals. The details of our work have been carried out on the following aspects: Laser induced thermal-reactions characteristics of differently-sized scattering defects were investigated. The precursor defects properties were also analyzed with models. The size and absorption properties were estimated. It’s clearly that micron/sub-micron scale defects are low/medium fluence precursors, respectively. The results provided direction for process optimization of crystals growth. Combining with control of crystals growth process, scale effects in defect and laser-induced damage in I-type KDP crystals were studied by an intelligently designed experimental plan. It’s found smaller size of precursor defects could lead to better damage resistance at 1064nm in I-type KDP. The 1ω laser damage mechanism in I-type KDP was comfirmed as laser induced thermal response. The scale effects could also obtained by simulation based on linear absorption heat diffusion model; then the defect size range responsible for 1ω laser damage in I-type KDP was further clarified; this could provide key parameters of guidance and theoretical basis for process optimization of crystals growth by continuous filtration technology. Laser damage performance at 355nm was investigated; bulk absorption in II-type DKDP crystals was reduced and laser damage resistance was also improved in a degree by laser pre-irradiation at 355nm. Moreover, band gap and nonlinear absorption properties were also studied; it's comfirmed that defect level exist in DKDP crystals, and nonlinear absorption process associated with defect level may be the dominated process in high fluence laser inducing damage in II-type DKDP crystals. Meanwhile, it’s found the defect level could be controlled by laser intensity, and this could provide theoretical guidance for laser conditioning protocols. Finally, it’s also demonstrated that laser conditioning mechanism in II-type DKDP crystals is mainly related to the mitigation of nonlinear absorption. Laser conditioning properties and technology for I-type KDP and II-type DKDP crystals were investigated. With the knowledge of laser damage mechanisms, laser conditioning protocols utilizing laser operating at 355nm for I-KDP crystals, and sub-nanosecond laser at 355nm for II-DKDP crystals were established It's also proposed and proved a "sub-nanosecond laser & nanosecond laser" conditioning protocol for further improving the laser damage resistance due to presursors always have widly size and absorption distributions.
学科主题	光学工程
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/30941]
专题	中国科学院上海光学精密机械研究所
作者单位	中国科学院上海光学精密机械研究所
推荐引用方式 GB/T 7714	王岳亮. I类KDP和II类DKDP晶体激光损伤机理及激光预处理特性研究[D].

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