超短脉冲激光在电介质材料中传输及破坏深度微观理论计算

Microscopic theoretical investigation on propagation and breakdown depth of ultrashort-pulse laser in dielectrics

基于Fokker-Planck方程和激光传输方程建立超短脉冲激光在电介质材料中的传输及材料破坏理论模型,计算材料内不同位置处导带电子数密度及激光电场强度随时间的变化,进而得到激光的反射率、透射率及沉积率随激光能量密度的变化特征.选取导带电子数密度阈值作为材料破坏的判断条件,计算了不同激光能量密度下的破坏深度,发现破坏深度随激光能量密度的变化曲线呈现先增长后减小,讨论了激光能量沉积特性对破坏深度的影响.计算最大破坏深度随激光脉宽的变化发现,激光脉宽越短则最大破坏深度越小.

Based on the Fokker-Planck equation along with laser propagation equation,a theoretical model that describes the ultrashort-pulse laser propagation characteristics and breakdown in dielectrics is established.Using this model,the conduction band electron densities and the electric field intensities at different positions in a dielectric material at different time are calculated.The variations of reflection,transmittance and energy deposition rate with input laser energy density are discussed.With the threshold conduction band electron density criterion,the breakdown depth in the material under varying laser energy density is calculated,which is found to increase first with laser energy density,and then to decline after reaching a maximum value.Effect of the spatial distribution of laser energy deposition on breakdown depth is analyzed.Meanwhile,the maximum value of breakdown depth is found to decrease as the laser pulse duration becomes shorter.