有机薄膜中纳秒激光冲击波的时间分辨拉曼光谱实验研究

发布时间：2018-05-06 18:15

本文选题：激光驱动冲击波 + 时间分辨拉曼光谱　；参考：《哈尔滨工业大学》2015年硕士论文

【摘要】：当一束功率密度达到GW/cm2以上的激光脉冲辐照到金属表面时,表层金属材料将被瞬间气化并点燃等离子体,后续注入的激光能量将继续支持等离子体云膨胀,从而在被辐照材料内部形成一系列的压缩波。这些压缩波不断地追逐,叠加,增强,最终形成冲击波。激光驱动冲击波现已成为实验室动高压主要加载手段之一,在冲击化学、微结构加工、激光支持爆轰波和惯性约束核聚变等领域都有着广泛的应用。作为一个高速流逝的暂态过程,激光驱动冲击波的表征及材料在冲击波加载下的超快动力学响应过程一直是研究的热点和难点问题。利用时间分辨拉曼光谱技术,可以在研究激光驱动冲击波传播特性的同时,对材料的冲击动力学响应过程进行实时、在线的实验测量研究。一般地,自发拉曼信号的激发效率极低。在激光冲击波作用下,材料的自发拉曼信号很容易被噪声信号所湮没,是该研究领域中亟待解决的一个主要问题。本工作旨在通过对冲击拉曼光谱实验系统的设计和优化,提高激光冲击波实验中拉曼光谱信号的信噪比,为有机薄膜材料的冲击动力学研究提供具有重要参考价值的研究数据和实验方法。本工作将超短脉冲激光驱动冲击波技术与时间分辨拉曼光谱技术相结合,设计并搭建了适用于激光驱动冲击波实验的时间分辨拉曼光谱系统,研究了该系统中主要光学元器件参数对拉曼光谱信噪比、空间分辨率等重要实验参数的影响。利用优化后的冲击拉曼光谱实验系统,实现了纳秒激光冲击波作用下有机薄膜材料蒽冲击拉曼光谱信号的单次采集,光谱时间分辨率达10 ns。采用约束结构的靶材,本工作系统地研究了纳秒激光冲击波在多晶蒽的有机薄膜中产生、加载和卸载的全过程。通过分析时间分辨拉曼光谱数据,得出纳秒激光冲击波在多晶蒽薄膜材料(厚度为160±10μm)中的传播速度为3.04±0.19 km/s,冲击加载过程中的峰值压力达~2.3 GPa,冲击波前沿宽度为~4.8μm,压力上升时间为~1.54 ns,冲击波在薄膜材料的传播时间为~50 ns,冲击压力卸载时间为~170 ns。
[Abstract]:When a laser pulse with a power density of more than GW/cm2 irradiates the metal surface, the surface metal material is instantly vaporized and ignited, and the subsequent injection of laser energy will continue to support the plasma cloud expansion. Thus a series of compression waves are formed within the irradiated material. These compression waves continue to chase, stack, enhance, and eventually form shock waves. Laser driven shock wave has become one of the main loading methods of dynamic high pressure in laboratory. It is widely used in the fields of shock chemistry, micro structure processing, laser supporting detonation wave and inertial confinement fusion. As a high-speed transient process, the characterization of laser-driven shock wave and the ultrafast dynamic response of materials under shock wave loading have been hot and difficult issues. The time-resolved Raman spectroscopy can be used to study the characteristics of laser-driven shock wave propagation at the same time to study the impact dynamic response process of materials in real time and on-line experimental measurement. In general, the excitation efficiency of the spontaneous Raman signal is extremely low. Under the action of laser shock wave, the spontaneous Raman signal of the material is easily annihilated by the noise signal, which is a major problem to be solved in this research field. The aim of this work is to improve the signal-to-noise ratio of the Raman spectrum signal in the laser shock wave experiment through the design and optimization of the shock Raman spectrum experimental system. It provides important reference data and experimental methods for the study of impact kinetics of organic thin film materials. In this work, we combine ultrashort pulse laser driven shock wave technology with time-resolved Raman spectroscopy, and design and build a time-resolved Raman spectrum system suitable for laser driven shock wave experiment. The influence of the main optical component parameters on the SNR, spatial resolution and other important experimental parameters of the system is studied. The single acquisition of shock Raman spectrum signals of organic thin film materials under nanosecond laser shock wave is realized by using the optimized experimental system of shock Raman spectroscopy. The spectral time resolution is up to 10 ns. The whole process of nanosecond laser shock wave generation, loading and unloading in organic films of polycrystalline anthracene has been systematically studied by using a confined structure target. By analyzing time-resolved Raman spectrum data, The results show that the propagation velocity of nanosecond laser shock wave in polycrystalline anthracene film (160 卤10 渭 m) is 3.04 卤0.19 km / s, the peak pressure during shock loading is 2.3 GPA, the width of shock wave front is 4.8 渭 m, the pressure rising time is 1.54 ns, and the shock wave is in film. The propagating time of the material is 50 ns and the unloading time of impact pressure is 170ns.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.2

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