Study On Dual-wavelength Interference Of Laser Plasma Electron Density Under Different Gas Pressures

As a product of the interaction between laser and matter,laser plasma has huge application potential,and different pressure environments will have a great impact on the properties of laser plasma.Therefore,studying the parameter changes of laser plasma under different pressures will help to better understand the mechanism of laser plasma,which is of great significance to the application of laser plasma technology.Aiming at the influence mechanism of atmospheric pressure environment on laser plasma,this paper establishes a dual-wavelength Mach-Zehnder transient interference device,and studies the influence mechanism of different delay time and different atmospheric pressure on the electron density of laser plasma.First,a dual-wavelength-based Mach-Zehnder interference experimental device was established.The digital delay generator is used to precisely control the time delay between the laser plasma induced Q-switched pulsed laser and the diagnostic pulsed Q-switched laser to realize the collection of different time series of interference fringes.At the same time,change the atmospheric pressure environment to obtain laser plasma interferograms under different delay times and different atmospheric pressures.Secondly,a software for processing transient interference fringe patterns was developed,and the laser plasma interference image was reconstructed by two-dimensional Fourier transform.The branch-cut algorithm was used to unwrap the winding phase to obtain a continuous laser plasma phase.Distribution information:According to the basic principle of Abel inverse transformation,the Hankel-Fourier numerical algorithm is used to obtain the laser plasma refractive index distribution information.Finally,according to the relationship between plasma electron density and refractive index,the relationship between laser plasma electron density and gas pressure is obtained.The results show that the electron density of laser plasma is increasing with the increase of pressure.When the delay time is 30ns and the pressure is 55kpa,the laser plasma electron density is the lowest(10¹⁹m^-3),and as the pressure increases,the electron density value increases,and when the pressure is 101kpa,the electron density reaches the maximum(6×10-9cm^-3).Compared with the delay time of 30ns,when the delay time is 90ns,the electron density change trend remains unchanged under different air pressures,and both increase with the increase of air pressure,but the overall value is reduced.When the pressure is 55kpa,the electron density is about 3×10¹⁸cm?3,and when the pressure is 101kpa,the electron density is about 2×10¹⁹ cm^-3.