单晶硅反射镜激光能量吸收系数与衬底表面质量的关联

高能激光系统中,单晶硅基底反射镜的能量吸收系数是影响系统性能的关键指标。衬底加工质量对镀膜后元件激光能量吸收系数影响显著。通过测试不同衬底粗糙度、划痕密度的单晶硅反射元件,分析衬底表面典型加工特征(粗糙度、划痕)对激光能量吸收系数的影响规律,认为粗糙度与吸收系数正相关,粗糙度均方根从0.668nm降低至0.345nm会使吸收系数降低28.0%。少量划痕对吸收系数的直接影响并不明显,吸收系数均值变化在3.1%以内。但表面划痕会诱发激光损伤,划痕密度较大时会引起后续能量吸收持续增大,辐照400s后,吸收系数较辐照100s时增大18.3%。

Correlation research between substrate surface quality and laser energy absorption rate for mono-crystalline Silicon reflector

In high energy laser systems, the energy absorption rate (EAR) of mono-crystalline silicon reflector is a vital index in the term of elements quality. The substrate process quality affects the EAR of coated optics dramatically. The surface roughness and scratch density for a series of silicon optics were measured. Based on the result, the co-influence and relationship between surface characteristic and EAR were analyzed. It is indicated that, surface roughness level is positively correlated to EAR and decides the global average rate of the entire surface. When the root-mean-square of roughness falls from 0.668nm to 0.345nm, the EAR decreases by 28.0%. In contrast, few scratches do not distinctly raise the EAR, the fluctuation is less than 3.1%. However, the surface scratch may generate laser-induced damage. Furthermore, when the scratch density is large enough, the subsequent EAR will grow constantly, for example, the amplitude reaches 18.3% after the 400s irradiation, compared with 100s irradiation.