面向大尺寸、高密度光栅的并行激光直写新技术研究

With the urgent demand to further improve the density of pulse compression grating(PCG), a key optical element in the laser ignition project,we propose a new technology for parallel laser direct writing system. Based on radial polarized light and binary phase plate, we can not only obtain the spot beyond the diffraction limit，which meet the requirement of increasing the pulse compression grating density, but also greatly extend the depth of focus，which can improve response of servo focusing system, therefore,the speed of laser writing system have one order of magnitude improvement with better uniform of grating mask.In additon,the quality of grating mask can be greatly improved with the stronge longitudinal electric field formed around the focal plane,beside,the uniformal distribution of energy density can reduce the influence of pithch vibration of mobile stage and hence improve the yield of productions of grating mask. It is demonstrated from our experiments that the spot quality has been greatly improved in the same writing speed compared with the traditional parallel laser direct writing technology.In addtion, based on this new technology,the grating mask with grating period of 500nm and line width less than 250 nm have been fabricated,which can fully the actual requirement of our project.

针对国家激光点火工程中对核心器件-脉冲压缩光栅密度进一步提高的迫切需求，基于径向偏振光和二元相位板，提出了一种并行激光直写光栅的新技术，设计合适的二元相位板，在高数值孔径的情况下，不仅可以实现超越衍射极限的光斑，满足脉冲压缩光栅密度不断增大的要求，同时大大延长了系统的焦深，降低了对伺服聚焦系统响应速度的要求，克服了在高速刻写过程中，曝光条纹不均匀的问题，使并行激光直写的速率有了数量级的提升。利用径向光聚焦在焦点形成的强纵向电场可以提高条纹对比度，提高光栅掩膜的质量，同时聚焦激光束纵向能量密度均匀分布，可以大大改善移动平台pitch抖动带来的不利影响，提高光栅的直写成品率。实验表明，相比于传统的并行激光直写光栅技术，本申请提出的新技术，在相同刻写速率的情况下，刻写光斑的质量有了明显的改善，制备出的光栅掩膜周期500nm，线宽小于250nm，完全满足实际的工程需要。

光栅是一个传统的、广泛使用的光学元件，也是激光聚变工程等多个大型光学工程领域的关键器件，大尺寸的脉冲压缩光栅价格极其昂贵，而且西方发达国家对我们实施禁运，我国大型激光工程所需的光栅只能依靠自主开发。. 在基于达曼光栅的并行激光直写的基础上，开展大尺寸、高密度光栅的制备技术研究，发明了旋转达曼光栅技术，实现了皮米级光栅周期均匀度的调谐。通过旋转二维达曼光栅，使得形成的光斑点阵相对于垂直扫描方向旋转一个小角度，通过高精度电动旋转台，实现周期精度皮米级调谐；设计了调平聚焦伺服系统，该系统可用于大面积光栅刻写，实验表明本系统装置能获得良好的稳定性与灵敏度的探测曲线，测量精度可达到纳米量级；利用大行程、高精度的气浮移动平台，采用101路达曼光栅并行激光直写，实现了尺寸达450mm*300mm的光刻胶光栅掩膜，达曼光栅的发散角0.3mrad，显微物镜数值孔径0.45，最终实现的光栅周期达到3um。. 这一技术为更大面积光栅的研制奠定了基础，为大面积、高精度衍射光学元件的制备提供了重要的手段。