用离子束溅射的方法在红外石英玻璃基底上制备了Ta2O5/SiO2（1.064 μm波长下高透，2.128 μm波长下高反）波长分离膜，利用飞秒激光系统（输出波长为2 μm，脉宽为80 fs）测试了它的激光损伤情况，同时用光学显微镜和扫描电镜观察了样品的损伤形貌，根据不同能量作用下破斑面积与能量密度的关系拟合得到样品的损伤阈值。实验结果表明，2 μm飞秒激光作用在波长分离膜的损伤形貌为层状分布，破斑边缘比较清晰，没有热扩散和热传导现象，属于本征损伤。利用基于导带电子数密度的理论模型，并结合电场分布与带隙理论讨论了2 μm飞秒激光作用于光学薄膜的损伤机制，确定了损伤起源于高低折射率界面处的窄带隙材料。

Laser-induced damage test of the sample is performed in a femtosecond laser system with duration 80 fs, centre wavelength of 2 μm. A wavelength separation multilayer of Ta2O5/SiO2（HT at 1.064 μm & HR at 2.128 μm）serves as the target, which is prepared by ion beam sputtering (IBS) on infrared glass. Meanwhile, damage morphologies of the sample are observed by Leica optical microscopy and scanning electron microscope (SEM). The laser-induced damage thresholds (LIDT) of the sample is calculated through the relation between damage area and laser fluence. It is found that damage morphology of the sample is layered, clear edges are easily seen around the damage spot, and the damage crater has no obvious sign of heat diffusion and conductance which means the femtosecond LIDT is closely related to intrinsic characteristics of materials. A theoretical model based on conduction band electrons is applied to discuss the phenomenon. Combining with electric field distribution and band-gap of materials we consider that the damage of the sample under 2 μm femtosecond laser pulse irradiation will first occur in the narrow band-gap material at the interface between high-index and low-index layers.