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题名	超短脉冲激光与固体材半豺目互作用和相位匹配强场高次谐波研究
作者	刘智
学位类别	博士
答辩日期	2002
授予单位	中国科学院上海光学精密机械研究所
导师	李儒新
关键词	超短脉冲激光 激光与物质才目互作用 气体高次谐波
其他题名	Study on the Interaction of Ultrashort Pulse laser with Solids and the Phase Matched High-Order Harmonic Generation
中文摘要	随着超短超强激光技术的迅猛发展，目前在小型化台式激光系统上，已经实现了时间宽度为光周期量级（巧色）的近红外超短激光脉冲，可聚焦功率密度已经达到了一1019W/cm2量级，这为激光与物质在极端物理条件下的相互作用研究提供了可能。本论文的工作主要是研究超短脉洲徽光与物质相互作用，特另。短脉冲激光加热金属材料，超短脉冲激光对透明介电材料的烧蚀破坏和相位匹配强场气体高次庇波的产生等，取得了如下成果：1．在理论上对飞秒超短脉冲激光与金属平面靶相互作用中主要物理过程的能量损耗进行了详尽的分析。研究表明，在飞秒超短脉冲激光与金属平面靶相互作用中，自由电子基本上没有通过热流传导向靶材内部传递能量，也没有通过自由电子－声子之间的能量耦合向晶格传递能量；根据这一结论，我们利用一维，双温度模型推导了自由电子温度的解析解。结果表明，在飞秒超短脉冲激光作用下，自由电子温度的大小基本上不再依赖于金属材料自身的性质，而只是决定于入射激光的参数。另外，罚门还首次推导出了超短脉冲近似假设成立的脉宽限制条件表达式和超短脉冲激光加热金属平面靶过程中自由电子的最高温度表达式。2．用量子力学方法对超短脉冲激光照射下透明材料中导带电子的激光能量吸收收和雪崩电离过程进行了计算。研究表明，在激光脉冲的前期，自由电子主要通过多光子电离的方式产生，而在脉冲的后期则主要是通过雪崩电离的方式产生。洲门通过理论模型求解了透明介质中自由电子密度随时间的演化方程。结果表明，自由电子速率方程中电子一空穴的复合过程以及电子的热扩散过程可以忽略。据此我们还计算出了材料的破坏闽值与入射脉冲宽度的关系，其计算结果与实验结果符合得很好。3．研究了飞秒超短脉冲激光辐照固体材料时的热力学效应和烧蚀破坏过程，在实验上比较了飞秒、皮秒和纳秒激光对材料烧蚀破坏过程所造成的物理形态上的不同。4．通过建立理论模型对超强短激光冲与毛细管中，隋性气体原子相互作用产生高次谐波的相位匹配过程进行研究，计算结果和实验结果相符。结果表明，通过调节一些参数，如气体气压，毛细管半径，可以实现毛细管中高次谐波的最佳相位匹配。首次发现了特定级谐波相位匹配中截止驱动光强的存在，它决定着能够达到相位匹配的最高谐波级次，是对高次谐波产生过程中已有的闭阈值光强概念的重要补充。分析表明要使更高级次的谐波获得相位匹配，需要更短脉宽的驱动激光脉冲以及更大电离能的气体工作介质。另外洲门还对毛细管中的谐波选择性进行了研究并指出了改善谐波选择胜的措施。5．掷门还对短波长高次谐波的实验探测仪器－晶体谱仪进行了研究，提出并设计了一种新型的平面晶体谱仪，可以在不知光源位置和没有任何参考谱线的情况下用以实现X射线谱线波长的精确、直接的标定。
英文摘要	With the development of ultrashort pulse laser technology, infrared laser pulses with few-cycle-duration (<5fs) and the laser intensity on the 1019W/cm2 scale have been available on a compact table top, which makes it possible to investigate laser-matter interaction under extreme physical conditions in laboratories. In this thesis, the interaction between ultrashort pulse lasers with matter, especially the heating of metal targets by ultrashort pulse laser, the ablation of dielectrics and the phase matched generation of high-order harmonics in gases, are investigated. The main results are as follow: 1. The interaction of ultrashort laser pulses with planar metal targets is investigated theoretically. The energy flow in the process of femtosecond heating is calculated in details. The results show that, in comparison with the energy absorbed by the overdense plasma, the energy loss for the ionization of the target, the thermal conduction and the electron-phonon coupling is so little that can be neglected under the approximation of ultrashort laser pulse. The electron temperature as a function of time is derived based on the one-dimension, two-temperature models. A conclusion can be deduced from the calculations that the electron temperature is nearly independent of the metal species for the heating by ultrashort laser pulse. Under the approximation of ultrashort pulse, the range of pumping laser duration and an expression of the highest electron temperature has been obtained. The rate at which conduction band electrons absorb laser energy and the avalanche rate are calculated using Ihe quantum mechanical model. The equation of the evolution of conduction-band electrons is solved numerically, and it is found that for both conduction band electrons-hole recombination and conduction band electrons diffusion are not important The dependence of the avalanche breakdown threshold on laser pulse duration is presented and the result agrees well with experimental results. The thermal effect and ablation mechanism of ultrashort-pulse laser ablation of materials are discussed. Some experiment results of femtosecond pulse ablation, and the comparison with nanosecond and picosecond laser pulses ablation are presented The phase matching of high-order harmonics generated in rare gases confined in a hollow fiber wave-guide is investigated theoretically. The calculated results are consistent with the experimental results. The phase-matched high-order harmonic generation in a gas-filled hollow fiber can be obtained by adjusting some parameters such as the gas pressure, the radius of fiber etc. A cutoff intensity for a certain phase-matched harmonic is found, which defines the highest order of phase-matched harmonic. The calculations show that a shorter laser pulse and the medium with a higher ionization potential are necessary for generating phase-matched higher-order harmonic. The possibility of favorably generation of a certain order or several orders of harmonic in Ihe hollow fiber wave-guide is investigated. Several measures of realizing the possibility are advised. A new design of x-ray crystal spectrometer for the measurement of short-wavelength high-order harmonics is proposed. It is possible to measure Ihe wavelength of spectral lines by using this new type of crystal spectrometer without any reference line.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15414]
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	刘智. 超短脉冲激光与固体材半豺目互作用和相位匹配强场高次谐波研究[D]. 中国科学院上海光学精密机械研究所. 2002.

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