光束整形用连续面形衍射光学元件的设计及面形控制研究

Laser beam shaping with diffractive optical elements is considered to be one of the most effective and promising beam shaping techniques. However, many experimental results show that serious speckle noise exists in the shaping beams, which greatly reduces the uniformity of the beams and limits the practical application of this technology. Although many scholars have proposed some methods to suppress speckle noise, it is at the expense of diffraction efficiency and can not meet the practical needs of low speckle noise and high diffraction efficiency. In order to solve this problem, this project proposes the use of continuous surface diffractive optical elements to achieve low speckle and high efficiency beam shaping. By improving the existing design methods, the phase distribution of continuous surface diffractive optical element can be obtained to eliminate the laser speckles caused by the uncontrolled random and irregular phase distribution on the output plane. Then the moving mask and the moving gray scale method developed by the project group are adopted to fabricate the continuous surface diffractive optical element. This method can not only achieve high diffraction efficiency, but also avoid the problem of the traditional method. This project aims to solve the bottleneck problem in the application of diffractive optical elements in the field of beam shaping, and promote the practicality of diffractive optical elements.

利用衍射光学元件的任意波面变换功能实现激光束的整形被认为是最有效、最有前途的光束整形技术之一。但是当前众多的实验结果表明，整形后的光斑中存在着严重的散斑噪声，极大地降低了光斑均匀性，限制了这项技术的实际应用。尽管很多学者提出了一些方法来抑制散斑噪声，但却是以牺牲衍射效率为代价，不能同时兼顾低散斑噪声和高衍射效率这一实用化的需求。针对该问题，本项目提出采用连续面形的衍射光学元件来实现低散斑和高效率的光束整形。通过改进现有的设计方法得到面形连续的衍射器件相位分布，以消除输出面上不受控的随机不规则相位分布造成的激光散斑；再基于项目组发展的移动掩膜和移动灰阶法实现连续面形衍射元件的一体化成型制备，不仅可以获得高的衍射效率，还可以避免传统的套刻工艺中累积的对准误差对输出光束质量造成的影响。本项目旨在解决当前衍射光学元件在光束整形领域应用中所遇到的瓶颈问题，推动衍射光学元件的实用化。

基于衍射光学元件的光束整形技术中，整形光斑中存在着显著的散斑噪声，极大地降低了光斑的均匀性。尽管很多学者提出了多种抑制散斑的方法，但却是以牺牲衍射效率为代价。针对该问题，本项目提出了一种连续面形衍射光学元件的设计方法，可同时实现高衍射效率和低散斑噪声的光束整形，在此基础上提出了一种用于激光分束的连续面形衍射光学元件设计方法，最后研究了连续面形衍射光学元件的加工工艺。针对光束整形的需求，研制了能将入射高斯光整形成线形和方形平顶光的整形器件，实测线性整形器件的衍射效率和均匀性误差分别为87%和2.7%，矩形平顶光整形器件的衍射效率和均匀性误差分别为84%和5.5%。针对激光分束的需求，研制了1×3和1×9两种一维激光分束器。实测1×3分束器的衍射效率为83.5%，均匀性误差为3.56%，1×9分束器的衍射效率为89.74%，均匀性误差为15.23%。这些指标表明提出的设计方法和所发展的加工工艺是可靠的，有效的。