基于光场计算和图像处理算法的激光自动对焦方法  

A Laser Autofocus Method Based on Light Field Distribution and Image Processing Algorithm

作　　者：习善明 李奇松 蒋金成 洪武庆 刘一 XI Shanming;LI Qisong;JIANG Jincheng;HONG Wuqing;LIU Yi(School of Optical-electrical and Computer Engineering,University of Shanghai for Science and Technology,Shanghai 200000,China)

机构地区：[1]上海理工大学光电信息与计算机工程学院,上海200000

出　　处：《光子学报》2024年第11期11-24,共14页Acta Photonica Sinica

基　　金：国家自然科学基金(No.62375174)。

摘　　要：针对飞秒激光三维加工中如何定量寻找焦点位置问题,提出了一种新型的计算光场分布与图像处理算法相结合的自动对焦方法。首先,根据Richards-Wolf矢量衍射理论推导经过物镜后激光在多层介质内的激光光场分布函数,并利用数值模拟求解高斯光束在各个介质不同位置处的光场分布计算结果,进而在理论上得到激光光束直径在多层介质中不同位置的变化关系。其次,实验中由上到下在多层介质中每隔相同离焦距离采集一系列光斑图像,通过感兴趣区域(ROI)、最大类间差法(Otsu)、Canny边缘提取等图像处理算法处理后,获取实际多层介质中不同位置处激光光斑直径以及激光直径随位置的变化曲线。最后,将理论与实验作对比并进行曲线校正,获得了实际激光光斑在多层介质中的变化曲线,以此建立基于计算光场分布和图像处理算法为基础的激光加工自动对焦方法。Femtosecond laser direct writing technology exhibits a variety of significant advantages compared to traditional micromachining technologies,such as the high processing resolution beyond the optical diffraction limit,a wide range of processing materials,and“real”three-dimensional structures fabrication.Due to these unique advantages,it is typically used for fabricating the micro-optical devices,biomedical devices,miniaturized electromechanical systems,etc.In aspect of the fabrication resolution,it usually depends on the use of the objective lens with the high numerical aperture in the femtosecond laser fabrication setup.Caused by the small depth of field of the high numerical aperture,it is easy to produce the out of focus effect,which leads to the error of the fabricated microstructures.Thus,it is vital and significant for quickly and accurately locating the laser focus on the surface of the sample during the micro-and nanostructures fabrication process.To solve the problem of quantitatively achieving the auto-focus function in femtosecond laser three-dimensional fabrication,this paper proposes a new type of automatic focusing method that it includes the computed light field distribution and the image processing algorithms.First of all,in the situation of tightly focusing of the high numerical aperture objective lens,the laser light field distribution function in the multilayer materials after passing the objective lens are derived according to the Richards-Wolf vector diffraction theory.Furthermore,the light field distribution results at the different positions of the medium can be solved by the numerical simulation of the laser light field distribution function.In the meantime,the laser beam diameter as a function of the position in the multilayer mediums can be also theoretically obtained.Secondly,a series of the laser beam images are captured in the interval of 2μm by moving the laser focus from top to bottom of the multilayer mediums.And the laser beam images are used for the image processing to obtain

关 键 词：激光自动对焦 光场计算 光斑图像处理 离焦量检测 边缘提取 

分 类 号：O439[机械工程—光学工程] O433.5[理学—光学]