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题名	超强超短激光脉冲与光学薄膜相互作用机理研究
作者	陈顺利
学位类别	博士
答辩日期	2013
授予单位	中国科学院上海光学精密机械研究所
导师	邵建达，赵元安
关键词	介质膜 飞秒激光诱导损伤 电场优化 多波长耦合 节瘤缺陷 激光预辐照
其他题名	Research on the mechanisms in ultra-intense and ultra-short laser interaction with optical coatings
中文摘要	随着超快激光技术的迅速发展，超快激光系统中光学元件的激光损伤问题逐渐成为研究的热点。作为超快激光系统中不可缺少的基本元件，光学薄膜也是激光系统中最薄弱的环节之一。研究超快激光作用下光学薄膜元件的抗激光破坏问题，对于阐释超快激光与光学薄膜作用的物理机制、以及探索改善薄膜材料抗超短脉冲激光损伤能力的途径，具有非常重要的实际意义。本文利用基于啁啾脉冲放大技术、中心波长800nm的Ti: sapphire飞秒激光系统，针对超快激光系统中常用的介质薄膜元件，包括谐振腔用高反射镜、光路中折返镜及脉冲压缩用关键元件啁啾镜，进行激光诱导破坏特性研究，具体工作如下： 证实了在飞秒脉冲时域电场优化设计作为介质薄膜元件的一种阈值提升技术的有效性。发现材料介电函数的瞬态响应对介质薄膜的飞秒损伤行为有重要影响，利用介电函数瞬态响应模型，对不同脉宽下介质薄膜样品优化前后的单脉冲损伤阈值给出了定量模拟；该模型核心思想是在飞秒激光作用的过程中，随着材料导带自由电子密度的增加，材料的介电函数是一个变量。 证实了在飞秒激光诱导介质薄膜损伤的过程中多波长的综合贡献，并分析了其中的热学响应和力学机制。发现在亚50fs脉冲激光作用下，啁啾镜表面损伤在较宽的能量密度范围内表现为圆形鼓包结构，并存在焦斑约束效应。提出了多波长耦合离化模型，对样品的损伤行为进行解释，结果表明在飞秒脉冲的整个谱宽范围内不同频率组分的光对破坏均有贡献。基于线弹性膨胀模型的应力演化分析表明，焦斑约束效应的出现对应于鼓包的演化从稳态膨胀向非稳态膨胀过程的转变。 微米量级、统计密度约为5000~20000个/mm2的节瘤缺陷对介质膜样品的飞秒损伤阈值和损伤形貌均无明显影响，但由于局部场增强效应，使得瘤局部破坏程度比基质更为严重。 发现纳秒激光预辐照对介质薄膜的飞秒激光损伤具有负面影响，证实了电子缺陷在飞秒时域有负面作用。纳秒激光预辐照以后介质薄膜飞秒损伤的主导机制并没有改变，仍然是本征的场致破坏机制，但是预辐照引入的电子缺陷则可以加速材料导带自由电子密度的演化，从而降低了其抗激光损伤能力。
英文摘要	With the boom of ultrafast laser technology, the breakdown of optical components in ultrafast laser systems gradually becomes the hotspot research. As the indispensable basic optics, optical coatings are also one of the most vulnerable spots in laser systems. Studies on ultrafast laser-induced damage (LID) of coating elements have significant practical meanings, including elucidating the mechanisms on ultrafast laser interaction with optical coatings, and exploring the pathways to improve the laser resistance of coatings. This dissertation aims to investigate the LID behaviors of commonly used coating elements, such as high reflectors used for cavity resonator, reflectors for adjusting the light path and chirped mirrors (CMs) acting as the key component in pulse compressors, by Ti: sapphire femtosecond laser systems operated at the central wavelength of 800nm based on chirped pulse amplification technology. Following are the main contents of the dissertation: Electric-field optimization is confirmed valid to improve the LID threshold (LIDT) of dielectric coatings in the femtosecond pulse regime. It is found that transient response of dielectric function can affect the LID behaviors of dielectric coatings significantly; transient response model of dielectric function is applied to quantitatively simulate the LIDT of samples with raw and optimized designs, irradiated by single femtosecond lasers with various pulse widths. This model reveals that, the dielectric function of materials subjected to femtosecond pulses is a variable with the accumulation of free electron density in the conduction band. Multi-wavelength contribution is verified existing in the femtosecond LID process of dielectric coatings, and relative thermal response and mechanical mechanisms are investigated. It is found that, irradiated by single 800nm-38fs lasers with spectral width of 35nm, the damage of CMs presents a circular blister feature at a wide range of laser fluence, and shows a confinement effect of focal spot. A multi-wavelength coupling ionization model is proposed to illustrate the LID behaviors of samples, which indicates that various frequencies within the spectral width of femtosecond pulse together contribute to the LID. Mechanical analysis with a linear-elastic buckling model means that, the occurrence of confinement effect corresponds to a transition point of blister evolution from stable-buckling to unstable-buckling process. Micron-level nodule defects with distribution density of about 5000~ 20000mm-2 have insignificant influence on the femtosecond LIDT and the damage morphology for dielectric coatings, while local breakdown within the defect region appears more severely than neighboring materials due to local enhancement effect of electric-field intensity. Nanosecond laser pre-irradiation is discovered to have negative effects on the femtosecond LID of dielectric coatings, which manifests the inconducive impact of electronic defects in the femtosecond regime. After nanosecond laser pre-irradiation, the dominant LID mechanism of dielectric coatings is still the electric-field-induced intrinsic breakdown, while the electronic defects introduced by laser pre-irradiation can accelerate the evolution of free electron density in the conduction, consequently leading to the weakening of femtosecond laser resistance of coatings.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15746]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	陈顺利. 超强超短激光脉冲与光学薄膜相互作用机理研究[D]. 中国科学院上海光学精密机械研究所. 2013.

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