短相干激光干涉微球全表面形貌高精度检测方法研究

Microballs are important parts in the region of inertial confinement fusion,micro-optics,precision machinery and so on.The surface roughness of microball influences its function and character greatly. However, the whole surface profiling of microball without point missing is very difficult in surface metrology field, especially for transparent microball. In this article, a new method of interferometry is presented to profile the whole surface of microball with high precision. The technology of low-coherence laser interferomety is adopted in this method to remove the influence of stray light. Phase-shifting interferometry is also utilized to reduce the influence of system noise and improve the precision of signal processing. A novel pin-hole mirror is designed to realize amplitude-wave interference and spare the light from transmiting in optical elements. Meanwhile, the random modes of the laser are filtered by single mode fiber to improve the laser quality. The whole surface of microball should be profiled by rotate scanning and patch splicing. The research would be focused on the structure and theoretical model of phase-shifting diffraction interferometry system with low-coherence, signal processing method with high precision, feedback scanning method, the method of error analysis and compensation, and so on. The technical specification as follows: Diameter of microball is between 400μm-2000μm, vertical resolution 5nm, horizontal resolution 1μm。.

微球在惯性约束聚变、微光学和精密机械等领域有着重要的应用，其表面微观形貌对其功能和特性有着重要的影响，而微球尤其是透明微球全表面形貌无遗漏检测是表面检测领域的难点。本文提出了一种新的干涉测量方法实现微球全表面高精度测量。采用短相干激光干涉消除杂散光对干涉场的影响；采用移相干涉技术，减小系统噪声的影响，提高信号处理精度；设计了一种新型针孔反射镜实现分波面干涉，减少了激光在光学元件中的传播环节，并采用单模光纤滤除激光杂模，提高了干涉光束质量；采用球冠扫描拼接实现微球全表面测量。重点研究短相干移相衍射干涉系统的结构、理论建模、高精度信号处理方法、扫描运动机构反馈控制方法、误差分析与补偿方法。检测指标：微球直径400μm-2000μm，垂直分辨率5nm，水平分辨率1μm。

微小球体是微光学、微机械等领域中最常见的元器件形态之一，其表面微观形貌对于其多方面特性有着重要的影响。传统检测手段存在着效率低、易损伤、易遗漏等问题。光学干涉测量法是较为理想的微球表面形貌检测方法，而目前仅有美国和法国的部分科研机构开展了相关的研究工作。本项目在对点衍射干涉测量理论进行深入分析的基础上，提出了基于偏振控制的移相衍射干涉微球全表面形貌检测方法，解决了传统光路分光式移相衍射干涉测量方法中必须使用短相干长度光源以及干涉信号对比度差的问题，使该方法适用于低反射率的微球表面形貌检测，并采用点衍射检测光波面畸变标定方法，提高检测精度。此外，针对机械式移相中普遍存在的线性移相误差，提出了基于误差互补修正的移相干涉测量相位提取方法，通过构造的五帧算法与经典Hariharan算法进行误差互补，大幅提高定步长解相算法的线性误差抑制能力，同时能够避免产生错误的虚数相位解，并对最小二乘相位解包裹算法进行了改进，使其适用于圆形域的相位解包裹。本项目还针对传统偏心误差修正方法残余误差过大的问题进行了研究，通过引入光程差数学模型的分析和高阶近似，实现偏心误差与Zernike误差项间的准确映射，提高偏心误差修正精度，提出了适用于微球检测的偏心误差修正方法。设计并搭建了用于微球全表面形貌检测的移相衍射干涉仪实验装置，并分别以低反射率的红宝石探头和GDP微球为检测对象进行了实际测量。实验结果表明：对比区域内形貌误差PV值和RMS值分别为66.17nm和16.89nm，与Wyko扫描白光干涉仪检测结果一致；测得红宝石表面粗糙度为0.0149μm，与厂家给定的标称值一致。GDP微球半球拼接后的赤道截面轮廓与原子力显微镜扫描结果基本一致。从而验证本项目提出方法的可行性和有效性。