Research On Mechanism Of Double-pulse Laser Strengthened Plasma Shock Wave

Laser shock processing?LSP?technology uses short pulse and high power density laser to irradiate the metal surface to make the material uniform and improve the fatigue resistance,wear resistance and corrosion resistance of the metal material.The characteristics of the laser induced shock wave determine the actual strengthening effect of the material.Compared with single pulse,double-pulse laser shock enhancement is to change the time domain characteristics of laser pulse to form a shock wave with stronger compression and longer duration.Therefore,research of the characteristics of the double-pulse laser-induced plasma shock wave helps to enhance the effect of laser shock processing,and provides better laser pulse waveform for optimizing the laser shock enhancement technology.In this paper,the mechanism of double-pulse laser strengthening plasma shock wave is studied experimentally,and the single and double laser pulse shock wave pressure and plasma physical parameters are measured.The double-pulse delays are set to be 30ns,20ns and 15ns respectively.Different energy distribution ratios are set under the same laser energy.The pressure of shock wave is transmitted by PVDF piezoelectric film.The interferometric measurement system is constructed for single and double laser pulse induced plasma shock wave.Two sets of delayed double pulse delays are 27.20 ns and38.65 ns respectively.The interferometric measurement is used to obtain the development process of plasma shock wave and to calculate the electron density of the plasma.The results of experiment show that the pressure of the double-pulse laser induced shock wave is significantly higher than that of the single pulse.When the three sets of delays have an energy distribution ratio of 1:1,the peak pressure increases the most.The shock wave of single pulse laser plasma is basically hemispherical and the shock wave with a high initial velocity drops rapidly.The delayed double-pulse laser causes a sudden change in the lateral displacement of the plasma shock wave.The distance and expansion speed of the double-pulse plasma are both larger than the single-pulse plasma at the same power density.The electron density of single-pulse plasma is basically10^{1 8}/cm³,which in the horizontal direction is high-low-high,and in the vertical direction gradually decrease from the center to edge.The electron density of the double-pulse laser plasma can reach 10¹⁹/cm³,and the delayed double pulse effectively prolongs the plasma impact time.the propagation characteristics of the double pulse laser induced plasma shock wave are summarized according to the experimental results,which are analyzed in combination with the balance relationship between the various effects.This topic explores the mechanism of the double pulse laser induced plasma shock wave,which provides a reference for the optimization direction of double pulse laser shock enhancement and a research reference for the industrial application of surface impact enhancement technology to provide better laser waveform.