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Plasma Acoustic Wave Diagnostics in Laser Shock Processing
L-C. Zhou, Y-H. Li, W-F. He, R-J. Liu and D-L. Chen

The high pressure plasma shock wave induced by nanosecond pulse and 1000 MW laser irradiation on the materials will also decay in the air and further form the plasma acoustic wave. The formation of plasma acoustic wave was analysed during laser shock processing and the signals with or without water restraint under different power densities were investigated experimentally. It’s found that the processing parameters have a remarkable influence on the amplitude of the plasma acoustic wave signals and low influence on waveform. The spreading speed of acoustic signal with water confining layer is higher than the speed of it without water confining layer, and higher power density also improves the amplitude of the signal. The variables are then analysed in order to evaluate correlations. The increase in intensity of signal is found to be essentially due to shock wave pressure. The envelop spectrums of the acoustic wave signal with the ablative layer well kept and broken are similar in high frequency area, while in the frequency from 0 to 80 kHz the envelop spectrums are quite different. It is supposed that the breaking of ablative layer reduced the creation efficiency of plasma, and the shacking frequency of plasma area is also changed. This method can be also applied for the acoustic wave diagnose in the interaction between laser plasma shock wave and materials.

Keywords: Laser shock processing, plasma acoustic wave, layered media, wavelet analysis, diagnostics

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