Effect Of Magnetic Field On Lifetime And Spectral Characteristics Of Femtosecond Laser Plasma

The plasma channel formed by femtosecond pulsed laser transmission in air have attracted extensive attention from domestic and foreign researchers in potential applications such as laser triggered lightning and atmospheric remote sensing.Among them,the key parameters,such as plasma channel length,ionization degree and life,are still hot research issues.In recent years,researchers have used the electric field,ns-fs,fs-fs,and femtosecond pulse sequences to achieve a certain effect in extending the life of the channel,but there is still a big gap for the actual application.This paper intends to measure the fluorescence radiation spectrum characteristics and supercontinuum spectrum of the plasma in the channel by using an externally magnetic field to affect the plasma channel,and study the life of the plasma to discuss possible physical mechanisms.In this paper,the experimental measurement of the forward supercontinuum spectrum and lateral fluorescence radiation spectrum of femtosecond laser plasma under 0~2.0 T external magnetic field is carried out.First,the forward spectrum measurement of the plasma through the integrating sphere shows that the intensity of the supercontinuum gradually increases during the increase of the femtosecond pulse energy from 0.25 to 1.5 mJ in the absence of a magnetic field,and continuously widens to the short wave direction at about 450 nm;after applying 1.0 or 2.0 T magnetic field,the intensity and broadening of the plasma supercontinuum did not change significantly compared to the absence of a magnetic field.Secondly,the time-resolved measurement results of the lateral spectrum of the plasma channel using an ICCD spectrometer showed that after the external magnetic field was applied,by adjusting the angle between the magnetic field and the laser direction,it was found that the plasma spectrum intensity changed significantly at the early stage of evolution;Double exponential fitting analysis of the 777.4 nm atomic line shows that the life of this line is increased by up to about 30% compared with the absence of the magnetic field.The physical mechanism of the increased line life may be the effect of the external magnetic field on the movement of the plasma,which delays the plasma Compound process.The research results will provide a certain reference for the related potential applications of femtosecond laser plasma channels.