基于跨尺度关联的大口径多层介质膜光栅制作无损检测

Multilayer dielectric grating(MDG) is one of the essential components for short-pulse, high-energy laser system.Its rigorous requirments,such as large aperture, good wavefront quality,high optical diffraction efficiency and high laser-damage threshold,exceed commercially available ones. Developing measurement techniques confirm surface and groove uniformity is also essential for obtaining optimum MDG performance.In the current project, a new nondestructive testing technique based on multiscale correlation for improving the quality of MDGs. To determine the microstructure profiles of MDG,scanning electron micrscopy(SEM), atomic force microscopy (AFM),optical microscopy(OM) and diffraction efficiency measurement over the entire grating aperture are collected and analyzed. A corresponding relationship between the OM image detail and SEM(AFM) ones will be established, after creating physical model for OM image detail.So image characteristics derived from OM and diffraction efficiency mesurement could be used to judge the suitable photoresist grating mask which meet the ion beam etching requirements, and uniformly high diffraction efficiency etched MDGs.This method can satisfy the requirments of simple operation, testing speediness and preciseness, which any inspection is not necessary to the MDGs microstructure parameters.

多层介质膜光栅是短脉冲强激光系统中的核心元件之一，其高衍射效率、高损伤阈值、良好波前和大口径的苛刻要求是普通商业光栅所远远不能满足的。大口径多层介质膜光栅制作工艺中，光栅微结构的有效、可靠检测是限制其发展及提高性能的瓶颈问题之一。本项目拟将研究一种新的基于跨尺度关联的提高大口径多层介质膜光栅性能的无损检测方法。利用扫描电镜、原子力显微镜、光学显微镜和衍射效率测量等常规检测手段，通过光学显微镜下图像特征的物理机制分析，建立光栅不同衍射效率分布区域的光学显微镜下图像特征与扫描电镜、原子力显微镜检测的光栅微结构之间的对应关系。从而利用衍射效率测量及光学显微镜下图像特征，就能方便地判断光刻胶光栅掩模能否进入离子束刻蚀和能否刻蚀出均匀的高衍射效率多层介质膜光栅。该方法操作简单、测量快速准确，不需要再检测光栅微结构。本项目的成功实施既丰富了光栅制作中的无损检测方法，也对大科学工程实际应用具有重要意义。

多层介质膜光栅是短脉冲强激光系统中的核心元件之一.利用严格的偶合波分析求解周期性结构衍射效率,分析了光源光谱和衍射效率拟合成结构色的方法.研究结果表明,基于结构色检测光栅占空比的方法可行,相关工作已在在大口径衍射光学元件研制中得到实际应用.在基金的资助下,本项目研究取得如下主要成果:.1) 给出了基于结构色无损检测方法测量光栅参数的基本原理和思路..2) 分析了光源参数(偏振和半高宽)以及光栅参数(线密度,栅线高度,占空比,光栅形貌等)对结构色的影响.光栅线密度在1740线/mm时,对应的结构色对线密度变化不敏感;栅线高度在300nm左右时,较小的栅线高度可以引起结构色较大的改变..3) 给出了线密度为1740线/mm的多层介质膜光栅的占空比检测的初步实验结果.光学显微镜测量系统中测量占空比的绝对误差在13%到20%,光谱检测系统中测量占空 比的绝对误差在3%到20%.