Research On The Dynamic Process Of Double-pulse Laser Plasma Based On Double-wavelength Interference

Double-pulse laser plasma is widely used in the fields of laser propulsion,element detection and laser shock enhancement,so it is of great significance to study its dynamic process.In this paper,we studied the mechanism of double-pulse laser-induced plasma.A dualwavelength interferometry system was established to study of the dynamics of dual-pulse laser plasmas with different delay times and different energy combinations.A dual-wavelength interferometry system based on Mach-Zehnder interferometer was built to diagnose plasma induced by dual-pulse lasers.The system uses DG645 to precisely control the time between the induced double-pulse laser and the time between the detection laser and the double-pulse laser,with a delay time accuracy of ±1ns.The series of interferogram of the double-pulse laser plasma was acquired based on this system.Then use the FFT transform method and Lissajous ellipse fitting method to process the phase of the interferogram to obtain the phase shift diagram.And then use the Abel inverse transform to obtain the plasma refractive index profile.Furthermore,the electron density distribution of the plasma was achieved.Based on the established dual-wavelength interferometric measurement system,the dynamic process of single-pulse laser and double-pulse laser-induced plasma was diagnosed.The results show that when the total energy of the double-pulse laser is equal to the single pulse,the electron density and expansion speed of the double-pulse laser plasma are both greater than that of the single-pulse laser plasma.The double-pulse laser induced plasma has an enhanced effect.The effect of the double-pulse delay time on the enhancement effect of double-pulse laserinduced plasma was studied.The trends of the electron density and expansion rate of the doublepulse laser plasma with the delay time are obtained by measurement.The results show that with the increase of the delay time of the double-pulse laser,the plasma electron density and expansion velocity increase at first and then decrease,but the delay time corresponding to the peak point is different.The enhancement effect of double-pulse laser-induced plasma with different energy combinations is studied.Through dual-wavelength interference diagnosis,the trend of the electron density of the dual-pulse laser plasma with energy is obtained.The results show that when the energy of the first laser beam unchanged,when the energy of the second laser is small,increase the energy of the second laser,and the plasma electron density increases.When the energy of the second laser is large due to the plasma shielding effect,the plasma electron density tends to be stable.In this paper,the dynamic process of double-pulse laser plasma is studied,and the influence mechanism of delay time and energy combination on laser plasma is explored,which provides a reference for the optimization direction of double-pulse laser-induced plasma.