通过对自由电子密度速率方程的简化,得到了计算光学击穿阈值的解析式.将计算结果与波长分别在可见光和近红外波段,脉宽分别为纳秒、皮秒和飞秒的激光脉冲在纯净水和含有杂质的水中实验测量的击穿阈值做了比较,吻合较好.对于纳秒激光脉冲,在纯净水中多光子电离提供初始电子,随后雪崩电离很快在电离的过程中占主导地位.对于短脉冲,多光子电离作用显得尤为重要,并且在击穿的过程中复合损失和碰撞损失对击穿阈值的影响逐渐消失.

An analytical expression of optical breakdown threshold for water has been abtained after simplifying the rate equation of free electron experimentally measured breakdown threshold picosecond and femtosecond laser pulses in the density.The calculating results have been compared with of pure water and impure water induced by nanosecond, visible and near-infrared. For nanosecond laser pulses, the generation of free electrons in distilled water is initiated by multiphoton ionization but then dominated by avalanche ionization. For shorter laser pulses, multiphoton ionization becomes more important, and the effect of collision and recombination on breakdown threshold losses gradually during breakdown. A good quantitative agreement is achieved between calculated and measured results.