飞秒激光与硅的相互作用过程理论研究

理解超短激光与材料的相互作用过程与机理是开展超短激光加工等工程应用的基础。首先引入电子激发项、双光子吸收、俄歇复合项等改进双温，使其较准确地适应于飞秒激光与半导体硅材料的相互作用过程。然后，分析了热损伤效应和非热损伤效应的影响。最后，开展了双脉冲飞秒激光与硅的相互过程研究，并分析了电子密度、晶格温度对于损伤积累效应的影响。理论模型得到单脉冲激光损伤阈值为0.25 J/cm2，此时主要表现为热损伤；当入射能量密度大于0.53 J/cm2 时，主要表现为非热损伤。双脉冲激光作用表明，脉冲间隔不大于100 ns（激光重频10 MHz）表现出明显的热积累效应，并显著降低损伤阈值。此时，第一个脉冲造成的电子密度升高（1026/m3）对损伤的贡献较小；而第一个脉冲引起的晶格温升将导致极高的电子激发以及晶格温升（800 K），对损伤起主要贡献作用。该研究对于激光微加工、激光防护等领域具有参考意义。

Theoretical research on dynamics of femto-second laser ablation crystal silicon

It is the foundation for engineering, such as laser micromachining etc., of understanding ultrafast laser interaction with materials. Firstly, it was introduced with band electron excitation, Auger recombination effect and two photon excitation etc. to modify present two-temperature model to adapt for the femto-second laser interaction with silicon. Then, the damage threshold was calculated. Thermal and non -thermal damage contributions were analyzed. Finally, two -pulse laser interaction with silicon was discussed. Also, Certain important parameters such as electron density and lattice temperature influence for heat accumulation effect were compared. The laser damage fluence is about 0.25 J/cm2. At this fluence level, thermal contribution dominates damage process, which is identical to experimental findings. With a fluence more than 0.53 J/cm2 non thermal damage mechanism prevails. With two pulses shooting, the heat accumulation effect is predicted, which shows that a time span between two pulses smaller than 100 ns (corresponding to 10 MHz repetition rate) cannot be ignored and it can reduce the damage threshold significantly. It is identified an electron density after the first pulse (lower than 1026/m3) does not significantly change the heating process. However, the lattice temperature after the first pulse (higher than 800 K) can cause serious electron excitation. This research is probably valuable in laser micromachining and laser protection applications.