飞秒脉冲的破坏阈值研究

Studying the damage threshold of femtosecond pulses

在Stuart等人理论模型的基础上,综合考虑Ming等人对电子密度衰减机制的研究,对飞秒激光的破坏机制进行了分析。通过计算模拟,分析了多光子电离、雪崩电离、电子衰减等机制与被辐照介质中自由电子密度之间的关系。分析表明脉冲宽度越窄,多光子电离过程提供的自由电子比例越小,其对激光破坏的作用也越小,此时雪崩电离过程将提供绝大部分电子,起到主导的作用;而随着脉宽增大,多光子电离提供的自由电子比例也将增大,其作用逐渐增强。当考虑衰减机制的影响后,电子密度在脉冲后沿不是维持在一个稳定的值,而是在达到极大值后呈下降趋势。在研究电子密度的基础上,利用计算飞秒脉冲破坏阈值的模型,分析了不同的衰减因子对破坏阈值的影响,研究表明,考虑电子衰减机制模拟得到的破坏阈值比不考虑时有所提高。

Based on the model established by Stuart et al.,and considering the research on electron density attenuation by Ming et al.,the damage mechanism of femtosecond pulse has been studied.The relationship between impact ionization,avalanche ionization,electron attenuation and free electron density has been studied.Calculations show that the shorter of the pulse duration,the less percentage of electron density produced by multiphoton ionization will be ,and the influence of it on laser damage will be less,too.Avalanche ionization plays a leading role,for it produced the most part of electrons.While for longer pulses,the influence of multiphoton ionization will increase gradually,and the percentage of electron density will also increase.When the electron attenuation was taken into account,electron density will drop after reaching the max.,rather than maintaining to a steady value.On the basis of studying electron density,using the model of damage threshold of femtosecond pulses,influences of electron density attenuation on damage threshold was analyzed.Calculations show that the threshold was higher than the one of the model that does not consider the attenuation.