激光诱导介质击穿中的脉冲截断问题

强激光与介质相互促进作用过程中,当自由电子的密度达到介质的损伤阈值时,介质将被击穿,脉冲的后续能量被激光等离子体强烈吸收而引发截断,这个时间点定义为截断时间点.脉冲的截断时间点对激光脉冲能量的传输有很大的影响.理论研究了入射激光脉冲能量对脉冲截断时间点分布的影响.定量分析和模拟了截断时间点对脉冲能量透过率的影响.模拟结果和实验结果符合很好.研究发现:激光脉冲能量透过率由脉冲截断时间点的位置决定.当脉冲截断时间点分布在脉冲前沿、峰值和后沿时,激光脉冲能垦的透过率分别对应小于50%,等于50%和大于50%.在线测量激光脉冲能量的透过率也可作为一种在线检测光学元件是否发生破坏的方法.

Study on Cut-Off Laser Pulse of Laser-Induced Dielectric Breakdown

In the process of the laser-matter interaction, when the density of the free electron reaches the damage threshold, the dielectrics will be broken down. Then, the subsequent part of the pulse energy will be strongly absorbed by the laser plasma, the light will be suspended, and this moment is defined as the cut-off time. The cut-off time makes a tremendous impact on the transmission of laser pulse energy. The effects of the input pulse energy on the cut-off time and the cut-off time on the pulse energy transmsstivity are discussed. The corresponding quantitative analysis and simulation are carried out, the simulation results and experimental results fit well. The pulse energy transmissivity is determined by the location of cut-off time. When the distribution of cut-off time at the pulse front edge, on the peak value and at the pulse back edge, the laser pulse energy transmittance will be less than 50%, equal to 50% and greater than 50% respectively. The on-line measurement of the laser pulse energy transmissivity also can be used for online inspection of damage of optical elements.