【作者】 赵瑞；

【导师】 倪晓武；

【作者基本信息】 南京理工大学 ， 光学工程， 2007， 博士

【摘要】 本文从理论和实验方面研究了高功率激光与物质相互作用过程中激光等离子体冲击波的产生、传输特性以及激光空泡动力学特性、空蚀机理，并对有关特征参数进行了实验测试和数值计算研究。利用自行设计的基于光纤耦合的双光束测试系统研究了激光致使空气中靶材表面产生的等离子体冲击波，实现了在一个激光脉冲内对激光等离子体冲击波瞬时速度的直接测量，避免因激光器稳定性或者激光等离子体冲击波可重复性而引起的测量误差，提高了实验精度。在对激光等离子体冲击波在不同介质中传输特性的研究方面，将“压缩波追赶与稀疏波卸载理论”引入冲击波发展及衰减过程的研究；从质量和动量守恒方程出发，解析研究了强激光等离子体冲击波的产生、发展和衰减机理。进而采用自行研制的光纤传感器跟踪探测等离子体冲击波的形成及发展过程，从实验验证了该理论模型的正确性。采用PZT水听器探测了波长为532nm和1064nm激光与水下金属靶材作用时产生的激光等离子体声波，并对实验获得的数据进行了时频分析。结果表明：该等离子体声波强度随激光能量的增大而增大；频率范围在0-150KHz，在频率为25KHz附近有一峰值；且频率范围和峰值位置基本不随作用激光能量以及靶材料的改变而改变。从基本的空泡动力学理论出发，推导了空泡各特征参量之间的关系，进而对空泡动力学模型进行了修正；采用有限差分法对空泡脉动进行数值模拟，得到了空泡脉动特性随液体粘性、空泡含气量、表面张力以及可压缩性的变化规律；实验上采用光偏转测试装置探测了激光空泡脉动以及空泡溃灭的细节过程，进而分析了液体粘性和作用激光能量对空泡脉动周期、泡半径及泡能等特征参数的影响。在系统地研究固壁面附近空泡溃灭过程的基础上，提出并研究了射流阈值、空泡在第一次和第二次脉动过程衰减蚀除机理以及空泡溃灭周期延长因子等问题。本文研究结果既可避免激光等离子体冲击波和空化带来的危害，也为合理利用激光等离子体冲击波和空化现象提供理论和实验依据，可供激光加工、激光医疗、水下激光加工和相关流体力学的研究参考。更多还原

【Abstract】 The laser-induced plasma shock wave evolution, cavitation bubble dynamics and thecavitation destruction mechanisms during the high-power laser and material interaction aresystemically investigated. Meanwhile, the characteristic parameters are measuredexperimentally and calculated numerically.By the self-developed dual-beam diagnostic technique based on fiber-coupling beamdeflection principle, the velocity of the shock wave can be determined in a laser pulseavoiding the error induced by the laser stability or the laser-induced shock waverepeatability.A theoretical model is proposed to describe the mechanism of laser-induced plasmashock wave evolution in different media. To verify the validity of the theoretical model,optical beam deflection technique is employed to track the plasma shock wave evolutionprocess. Good agreement has been established between theoretical and experimentalresults. It is shown that the laser-induced plasma shock wave undergoes three processes:formation, increase and decay process; the increase and decay of the laser-induced plasmashock wave are the result of the overlap of compression wave and rarefaction wave,respectively. In addition, the velocity and pressure distribution of the laser-induced plasmashock wave as a function of distance is presented.By means of a PZT hydrophone, the acoustic waves induced by a Q-switched Nd: YAGlaser with wavelength 1064nm and 532nm are detected. Based on Wavelet Packet Analysisand Smoothed Pseudo Wigner-Ville Distribution (SPWVD), the experiment data istime-frequency analyzed. The experimental results indicate that the amplitude of thelaser-induced acoustic waves increases with the laser energy; the frequency coverage isfrom 0 to 150 KHz, and in the meantime there is a peak located at about 25 KHz. Inaddition, the spectrum and the peak of frequency are basically stable in spite of the changeof laser energy and target texture.Based on the cavitation bubble dynamic theory, the relationships between eachcharacteristic parameter are deduced and then an amended cavitation bubble dynamicmodel is provided. Employing the finite difference calculus, the cavitation bubble pulsatingperformance with the change of liquid viscosity, gas content, surface tension and condensability is obtained. In the experiment research, the detailed processes of capitationbubble oscillation property and bubble collapse are gained by the fiber-optical detectionsensor. Furthermore, the influence of the liquid viscosity and laser energy on the bubblepulsation period, bubble radii and energy are analyzed.Based on the systematical investigation of cavitation bubble collapse near the solidboundary, the liquid-jet formation threshold is proposed. Meanwhile, the cavitation erosivemechanisms during the first two collapses and the prolongation factor of the collapse timeversus the non-dimensional parameter are discussed and established.The results described in this work avoid the harm induced by the laser-induced plasmashock wave and cavitation; what is better, these results provide the theoretical andexperimental reference to rational use of laser-induced plasma shock wave and cavitation,laser processing, laser lithotripsy, laser ophthalmology, and corresponding hydromechanics,etc.更多还原