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题名	飞秒超快激光在若干固体和气体介质中的能量沉积与非线性传输特性研究
作者	邓蕴沛
学位类别	博士
答辩日期	2005
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 激光与物质相互作用 石英 空气 等离子体通道
其他题名	Study on energy deposition and nonlinear propagation characteristics in solid and gaseous media by ultrafast laser pulse
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（＜sfs）的近红外超短激光脉冲，可聚焦功率密度已经达到了－1022w／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冲激光与物质相互作用，特别是飞秒超快激光在若干固体和气体介质中的能量沉积与非线性传输特性研究，取得了如下结果：1．实验研究了800nm飞秒激光作用下石英玻璃的破坏闭值和烧蚀规律，发展了雪崩击穿模型，计算了材料的烧蚀闰值与脉冲宽度的依赖关系，烧蚀深度、烧蚀体积与脉冲能量的依赖关系，研究了导带电子的扩散对材料中激光能量的沉积、分布，材料的破坏阂值和烧蚀规律的影响。结果表明，当脉冲宽度在飞秒量级时，材料的破坏闭值明显偏离热烧蚀规律，材料发生了雪崩击穿。研究了材料在800nm，70fs激光作用下材料的烧蚀面积、深度、体积与激光强度的依赖关系。根据雪崩击穿模型，理论计算了材料的烧蚀阈值与脉冲宽度的依赖关系，烧蚀深度、烧蚀体积与脉冲能量的依赖关系。理论结果与实验符合得很好。结果表明，导带电子的扩散对材料中激光能量的沉积、分布，材料的破坏阂值和烧蚀定标率都有重要影响。I2．实验研究了在8O0nm双脉冲飞秒激光作用下石英玻璃和单晶硅的破坏闭值。通过测量不同的双脉冲之间的延时，以及不同的第一个脉冲的能量所得到的醉坏闭值，研究了石英玻璃和单晶硅在飞秒激光辐照后，导带电子的驰豫时间。我们发现在相同的延时条件下，由于不同的吸收机制在双脉冲飞秒激光作用下石英玻璃和单晶硅的激光破坏闭值的变化趋势明显努同。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．使用纵向衍射的方法测量出等离子体细丝通道的直径和通道中电子的平均密度。从等离子体细丝通道中电子密度在时域的演化过程，发现电子密度可以维持的特征时间是纳秒（ns）量级。5．使用纵向衍射的方法测量出等离子体细丝通道的阂值，研究等离子体细丝随入射激光能量变化时从单丝到多丝的演化。利用纵向衍射的方法测量等离子体细丝通道中的自由电子密度，可以得到更精确的成丝阈值。同时可以由衍射环的变化能很细致灵敏地观察到等离子体细丝从单丝到多丝的演化。6．我们还发展了双脉冲飞秒激光的精确延时装置，提出并设计了一种新型的延时装置，可以精确测量两个汇聚在空间某点的超短激光脉冲相互间时间同步情况和延时量，主要适用于精密测量两个波长相同，偏振方向相同或相互垂直的超短激光脉冲汇聚在空间某点时相互间时间延时，测量精度到达数fs量级。提出了一种新的对自聚焦现象进行测量的方法，利用宽带的惆啾脉冲激光作为探针，采用横向偏振测量的方法能够对各种亚皮秒的超快过程如激光在各种气体、透明介质等材料中传输时的自聚焦现象进行单II发的实时飞秒时间分辨诊断测量。
英文摘要	As the rapid development of ultrashort and ultrafast laser technology, the pulse width of the near IR laser pulse has reached light cycle scale (<5fs) and the focusable power intensity has reached \022W I cm2, which provide the possibility for the research on the interaction between materials and laser pulse at some extreme physical conditions. This thesis focuses on the study on the interaction between materials and laser pulse, especially the ablation of transparent dielectric materials, the propagation of femtosecond laser pulse in air and the interaction between air and femtosecond laser. I. The damage threshold and the mechanism of ablation of fused silica by 800 nm laser pulse are investigated experimentally. And the relationship between the ablation threshold and the pulse width, also, the relationship among the ablation depth, the ablation volume and the energy of light pulse are numerically calculated. We also investigated the effect on the deposition and the distribution of energy, and the damage threshold of material and the ablation principle by the diffusion of the conduction band electrons. The results show that when the pulse width is of femtosecond scale, the value of ablation threshold is obviously deviated from the principle of ablation, the material experiences avalanche ionization. In the experiment we investigated the relationship among the ablation area, depth, volume of the material and the intensity of the laser pulse. According to the model of avalanche ionization, the relationship between the ablation threshold and the pulse width, and the relationship among the ablation depth, the ablation volume and the energy of light pulse are numerically calculated. The theoretical results agree well with the experimental results. The results show that, the diffusion of conduction band electrons affect obviously the energetic deposition. We investigate experimentally the ablation threshold of fused silica and silicon by using double light pulses. Through measuring the threshold with different delays of between the two pulses and different energies of first light pulse, we investigated*the relaxation time of conduction band electrons in fused silica and silicon irradiated by femtosecond light pulse. Also, we obtained the variation of different thresholds of fused silica and silicon due to different mechanism of absorbability in this experiment. The ablation process and thermodynamics of solid irradiated by femtosecond laser pulse is investigated. And we compared experimentally the physical differences in the ablation process by laser pulses of femtosecond, picosecond and nanosecond scale. We use the longitudinal diffraction method to measure the diameter of the plasma channel and the average density of the electrons. The characteristic time scale is of nanosecond scale from the analysis of the variation of electron density in the plasma channel generated in air. The laser energy threshold of the plasma channel is obtained by the longitudinal diffraction method, and we study the evolution from single filament to multiple filaments as the laser energy changed. Using this method, the threshold of filamentation can be determined more exactly. And we can observe the evolution from single filament to multiple filamentation according to the difference in diffraction pattern. Scheme for adjusting the interval in two femtosecond laser pulses is investigated, and a new delay method is proposed for facilitating the simultaneous characterizing and the proper delay between the two laser pulses at a specific point. It is suitable for the measuring of two laser pulses with the same pulse width and the polarization directions of the two laser pulses are the same or perpendicular to each other. The resolution reaches the scale of a few femtoseconds. A new method for measuring self-focusing is proposed. A chirped laser pulse with board spectrum is used as a probe pulse. By chirped femtosecond time-resolved optical polarigraphy, we can perform instantaneous time-resolved measuring in a single-shot basis.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15789]
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	邓蕴沛. 飞秒超快激光在若干固体和气体介质中的能量沉积与非线性传输特性研究[D]. 中国科学院上海光学精密机械研究所. 2005.

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