Studies On Characteristic Of Laser-induced Plasma Shock Wave Evolution And Cavitation Bubble Dynamics

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.