短脉冲激光辐照下SiO2损伤微观机理简化模型
A simple model of micro-damage mechanism of SiO2 under short pulse laser irradiation
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摘要: 从电子密度速率方程出发，建立短脉冲激光辐照下SiO2材料中导带电子增长简化模型，计算了SiO2中光致电离速率和电子雪崩速率，得到SiO2激光损伤阈值与脉冲宽度的关系，计算分析了光致电离和碰撞电离两种电离机制在导带电子累积过程中的不同作用。结果表明：脉冲较长，碰撞电离几乎能提供全部的导带电子，激光损伤阈值与脉宽的0.5次方成正比；脉冲较短时，导带电子主要由碰撞电离产生，光致电离提供碰撞电离的初始电子，激光损伤阈值随着脉宽的减小，先增加后减小。Abstract: Based on the rate equation of electron generation, a simple model of evolution of conduction electron under short pulse laser irradiation is employed to predict the laser damage thresholds of SiO2. The rates of impact ionization and photoionization are calculated and compared with each other. The threshold energy densities are obtained as function of pulse duration from 0.1 ps to 10 ns. The results show that for long pulse, the damage is dominated by impact ionization, and the thresholds are in proportion to the square root of pulse duration. While in the cases of short pulse, the damage is also governed by impact ionization but with photoionization supplying the seed electrons, and with decreasing pulse duration, the threshold first rises，then drops．
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Key words:
- impact ionization /
- photoionization /
- laser damage /
- threshold
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