基于激光偏振跳变的应力测量研究

The birefringence induced by the tiny internal stress in optical element influences the imaging quality of optical element. The split of optical element and accident happens when the internal stress in optical elemnt is big. The method of detecting the magnitude of stress birefringence is used to evaluate the stress status of optical element. The existing methods are the qualitative detecting. It is a disadvantage for the discovery and treatment in time. Thus, it is important for the stress detecting and the choose of high quality optical element to research the high precision technology of stress detecting, especially the technology for the tiny stress detecting. Here we studied the physical mechanism of the polarization flipping induced by the anisotropy feedback and the relationship between the position of polarization flipping and the stress magnitude. The physical model for the stress measurement is built. Based on the research results, the high precision detecting for the internal stress is realized. The physical mechanism of polarization locking phenomenon is researched. Based on the theoretical results, the method of releasing polarization locking is proposed and the tiny internal stress is measured. The variation law of the laser polarization states when the stress direction varies is researched. Based on the law, the stress direction is measured.

光学元件的微小内应力使其出现双折射现象，影响光学元件的成像质量，应力较大时，会使光学元件发生炸裂，引起事故。为评估光学元件的应力状态，常用的方法是检测光学元件的应力双折射大小。现有的应力双折射检测方法测量精度较低，满足不了应力高精度检测的需求。所以，研究高精度的应力检测技术，特别是能敏感微小应力的检测技术，对于微小应力的检测和高成像质量光学元件的选型，均具有重要意义。本项目针对应力高精度检测的需求，研究激光各向异性回馈偏振跳变的物理机理和偏振跳变点与应力大小的关系，建立应力测量的物理模型，实现对应力大小的高精度检测；研究激光偏振锁定现象的物理本质，基于理论研究结果，提出解除锁定现象的方案，实现对微小内应力大小的高精度检测；研究应力方向变化时激光偏振态的变化规律，基于此规律实现对应力方向的高精度检测。

光学元件内部的微小应力会使光学元件出现双折射现象，对光学元件的影响很大，在此应用背景基础上，本项目开展了激光各向异性回馈现象、激光偏振锁定现象的物理机理及锁定现象消除方案、应力方向对激光输出强度和偏振态的影响等研究，突破偏振跳变点与应力大小关系确定、偏振跳变锁定现象消除方案、偏振态随应力方向的变化规律等关键技术，开发了激光回馈偏振跳变应力测量系统。建立了应力大小与激光偏振跳变的关系，提出通过测量压电陶瓷电压计算应力大小的实验方案，消除了压电陶瓷非线性误差对测量结果的影响，实现了对应力大小的高精度测量，测量精度达到0.16度。报告中采用应力方向靠近激光偏振方向时经过检偏器后的激光强度变化曲线，实现了应力方向的测量。实验中发现，双折射晶体光轴方向与激光初始偏振方向存在夹角时，随着光轴方向与激光初始偏振方向夹角的变化，激光输出光偏振态发生变化。当光轴方向与激光初始偏振方向平行时，经过偏振光的光强度极值，最大或最小光强。即当双折射晶体快轴靠近远离激光初始偏振方向时，激光探测器检测到的电压随压电陶瓷驱动电压增长而增大，反之减小，据此可以实现对双折射原件光轴的高精度测量。基于应力测量系统，报告中同时测量了样品石英晶体的折射率和厚度，折射率测量精度优于0.0006，厚度测量精度优于59nm，级数测量无误差。非对称光学回馈是激光回馈的重要分支，本部分研究了非对称光学回馈现象。通过改变非对称光学回馈大小，观察到不同的强度调制现象。试验发现激光强度调制的振幅与非对称光学回馈大小成反比。基于激光回馈位移测量系统，研究了压电陶瓷的误差消除方案。椭偏仪是高敏感、非破坏的测量技术，用于测量表面参数，由于椭偏仪中所用的光学原件的相位延迟，在测量结果中引入误差。本文基于应力测量系统，修正了椭偏仪系统的测量误差，经修正后的椭偏仪系统误差测量精度优于1.2度。