大口径多层介质膜光栅衍射效率测量及其在制作工艺中的应用

多层介质膜光栅是高功率激光系统的关键光学元件.为了满足国内强激光系统的迫切需求, 在大口径多层介质膜光栅的研制过程中,建立了单波长自准直条件下的衍射效率测量方法及其误差分析. 结果表明误差主要由探测器的噪声和测试人员的差异产生,对衍射效率测试精度的影响是±1%. 在此基础上,将光栅衍射效率及其分布测量技术应用于光栅制作工艺中, 作为大口径光栅无损检测的一种手段,如判断光栅掩模是否能进行离子束刻蚀、 离子束刻蚀的在线监测和是否需要再刻蚀,从而实现对大口径多层介质膜光栅离子束刻蚀过程的定量、 科学控制,提高了离子束刻蚀光栅制作工艺的成功率.利用上述技术,已成功研制出多块最大尺寸为 430 mm× 350 mm、线密度1740线/mm、平均衍射效率大于95%的多层介质膜光栅. 实验结果表明,该方法操作简单、测量快速准确,不必检测光栅微结构. 为大口径多层介质膜光栅研制的无损检测工程化奠定了基础.

Diffraction efficiency measurement of large aperture multilayer dielectric grating and its application in the fabrication process

Large aperture multilayer dielectric grating (MDG) is one of the key elements of high-power laser systems. In order to meet the requirements for large aperture MLG in a high-power laser system, a diffraction efficiency measurement system is developed for characterizing the diffraction efficiency of large MDG at 1064 nm and Littrow mounting. Through analyzinge the main factors such as detector signal-to-noise ratio and operating staff, which influence the testing results during measurement, their difference is obtained to be less than ±1%, which proves that the method can be used to measure the diffraction efficiency of MDG. Based on a large number of experimental data, the optical characterization of MDG in a negative first-order Littrow configuration could provide some information about grating microstructure. So the diffraction efficiency measurements have a number of important applications in the fabrication process, as a nondestructive grating inspection tool, such as determining the suitable photoresist grating mask which meet the ion beam etching requirements, on line end-point detection during ion beam etching, and judging whether another etching is needed. Based on above techniques, a number of MDGs have been achieved, each of which has mean diffraction efficiency greater than 95% line density 1740 lines/mm, and aperture up to 430 mm×350 mm. The results show that this method can satisfy the requirements for simple operation, testing speediness and preciseness, in which any inspection is not necessary for the MDG microstructure paramters.