为了测量飞秒激光对多光谱滤波片的损伤阈值, 采用钛∶蓝宝石飞秒脉冲激光(800nm、50fs)对多光谱滤光片的前膜进行了激光损伤阈值的实验研究, 并使用显微镜观测了滤光片前膜的损伤形貌。结果表明, 薄膜在不同脉冲辐照次数(1, 2, 5和10)下, 前膜损伤阈值分别为1.68J/cm2,1.56J/cm2,1.44J/cm2和1.42J/cm2, 随着脉冲辐照次数的增加, 损伤阈值降低, 激光脉冲的重复辐射会对薄膜形成累积效应; 由于飞秒激光的宽度极短, 薄膜导带电子由多光子电离产生, 并迅速吸收激光能量, 当其能量大于材料的带隙能时, 会与价带电子发生碰撞产生另一个电子, 进而形成大量的自由电子, 对薄膜造成损伤; 在1-on-1和2-on-1测试方法下, 随着飞秒激光能量密度的增加, 前膜损伤区域的轮廓越来越清晰、规整, 并逐渐出现清晰的分层现象, 这归因于前膜干涉场的分布不同。该研究对多光谱滤波光膜在飞秒激光作用下的损伤效果提供了参考。

To measure the damage threshold of multispectral filter induced by femtosecond laser, the laser damage threshold of front film of the multispectral filter was experimentally studied by a Ti∶sapphire femtosecond pulsed laser (800nm, 50fs), and the damage morphology of the front film of the filter was observed by a microscope. The results show that the damage thresholds of the front film under different pulse irradiation times (1, 2, 5, and 10) are 1.68J/cm2, 1.56J/cm2, 1.44J/cm2, and 1.42J/cm2, respectively. The damage threshold decreases with an increase in the pulse irradiation number. The repeated laser radiation will form a cumulative effect on the film. Because the width of the femtosecond laser is very short, the conduction band electrons in the film are produced by multiphoton ionization and quickly absorb the laser energy. When the electron energy is greater than the bandgap energy of the material, it will collide with the valence band electrons to produce another electron. A large number of free electrons are generated, resulting in film damage. Under the 1-on-1 and 2-on-1 test methods, the morphology of the damaged area of the front film becomes more apparent and regular with the increase of femtosecond laser fluence, and a clear layered structure gradually appears. The phenomenon is due to the different distribution of the interference field in the front film. This study provides a reference for the damage effect of multispectral filter film under femtosecond laser.