超快激光诱导单晶硅瞬态光学性质演化机理

研究了从亚皮秒到皮秒范围内的不同脉宽和不同能量密度的激光作用下单晶硅材料表面瞬态光学性质的演化规律。这项工作基于考虑了相变潜热的双温方程、载流子数密度模型，通过计算激光辐照过程中的载流子温度、晶格温度和激发态载流子数密度和介电常数，模拟了光子到电子以及电子到声子的能量传递过程，最终得到了单晶硅表面折射率和消光系数的变化结果。有助于揭示亚皮秒到皮秒脉冲宽度范围的超短脉冲激光辐照下，单晶硅材料瞬态光学性质的演化机理。理论结果表明，若单个激光脉冲无法使单晶硅熔化，则不同的激光能量密度和不同的激光脉宽对最小折射率的影响非常有限，在0.3~0.4 J/cm2的激光能量密度范围内，每0.01 J/cm2的能量密度改变引起的最小折射率变化率小于0.5%。若单个激光脉冲能使单晶硅熔化，则不同能量密度和不同脉宽的激光对硅表面的折射率和消光系数有不同程度的影响。该研究结果可为基于超短脉冲激光的单晶硅材料加工和表面改性提供一定的理论指导。

Evolution mechanism of transient optical properties of ultrafast laser-induced monocrystalline silicon

The evolution pattern of the transient optical properties on the surface of monocrystalline silicon materials under the action of lasers with different pulse widths and different energy densities in the sub-picosecond to picosecond range was studied. This research was based on a dual temperature equation, carrier number density model, that considered the latent heat of phase transition. The carrier temperature, lattice temperature, permittivity, and the number density of excited carriers during laser irradiation were calculated, energy transfers processes from photons to electrons and electrons to phonons was simulated. In the end, the variation results of refractive index and extinction coefficient of the monocrystalline silicon surface were obtained. This result helps to reveal the evolution mechanism of the transient optical properties of monocrystalline silicon materials under the irradiation of ultrashort pulse lasers in the sub-picosecond to picosecond pulse width range. Theoretical calculations show that if a single laser pulse cannot melt monocrystalline silicon, the effects of different laser energy densities and laser pulse widths on the minimum refractive index and extinction coefficient are minimal. In the laser energy density range from 0.3 J/cm2 to 0.4 J/cm2, the minimum refractive index change is less than 0.5% per 0.01 J/cm2 change in energy density. Suppose a single laser pulse can melt monocrystalline silicon. In that case, different laser energy densities and pulse widths have different degrees of influence on the silicon surface's refractive index and extinction coefficient. This research results can provide some theoretical guidance for the processing and surface modification of monocrystalline silicon materials based on ultrashort pulse laser.