飞秒激光烧蚀硅的瞬态演化特性仿真

为深入揭示飞秒激光烧蚀硅的瞬态演化特性，建立了飞秒激光烧蚀硅材料理论模型，并进行了仿真研究。研究表明：飞秒激光可在脉宽时间内激发大量的电子，使其浓度超过损伤阈值，而此时晶格仍保持在较“冷”状态，直到1 ns量级才达到熔点温度；电子温度也会在脉宽时间内急剧拉升至104 K量级，随后将能量缓慢地释放给晶格，直到10 ns量级才与晶格达到热平衡。电子存在两次急剧升温的过程：第一次起于自由电子吸收，止于电子与晶格的能量耦合；第二次起于单光子和双光子吸收，止于脉冲结束。脉冲能量越大，电子密度和温度越高；脉宽越短，电子温度越高。
In order to further reveal the transient evolution characteristics of silicon ablated by femtosecond laser, the theoretical model was established, and the numerical simulation was carried out. The results show that the femtosecond laser can excite a large amount of electrons with its density exceeding the damage threshold in the pulse duration. At that time, the lattice remains in a “cold” state until it reaches the melting point temperature as long as 1 ns order of magnitude. The temperature of electrons dramatically increases to 104 K level in the laser pulse irradiation moment. And then the energy is released slowly to lattice and the thermal equilibrium is reached until 10 ns order of magnitude. The electron has two rapid warming processes. The first one starts from the free-carrier absorption, and stops at the electron-lattice energy coupling; the second one starts from the single photon and two photon absorption, and ends at the end of the pulse. It is found that the higher the temperature and density of electron are, the bigger the pulse energy is and the shorter the pulse duration is.