在超快激光照射过程中,金属靶材的光学性质是动态变化的。采用双温模型与分子动力学结合法,考虑动态和常数光学性质两种情况,对不同脉宽的超快激光照射下铜薄膜的热响应进行了模拟研究。其中,常数光学性质包括由激光沉积能量相等计算得到的等效平均反射率和室温下的吸收系数。结果表明: 两种情况下的电子温度和晶格温度均差别较小,尤其是脉宽远小于电子-晶格弛豫时间的飞秒激光;而当激光脉宽相当于或大于电子-晶格弛豫时间时,如皮秒激光,光学性质的动态变化对材料的熔化和重凝的影响则比较明显。

The optical properties of metal targets subject to ultrafast laser irradiation are dynamically changing. A hybrid method coupling the two-temperature model with molecular dynamics has been used to simulate the femto-and pico-second laser-induced thermal responses of copper films considering the dynamic and constant optical properties. The constant optical properties include an equivalent average reflectivity calculated by setting equally deposited laser energy and an absorption coefficient at room temperature. The results show that the electron and lattice temperatures are little different in both femtosecond and picosecond laser cases, especially for the femtosecond laser with a pulse width far less than electron-lattice relaxation time. As the laser pulse width is comparable to or greater than the relaxation time, e.g., the picosecond laser, the influence of the dynamic change of the optical properties on the melting and re-solidification of the material becomes more significant.