基于自参考干涉的光束质量M2因子测量方法及关键技术研究

Beam quality factor M2 is an important indicator to measure the performance of a laser beam, it’s also one of the most commonly and widely accepted parameters for beam quality evaluation and characterization method, and it’s has great significance in the fields of the laser’s theoretical analysis, design, manufacture and various applications. However, the traditional M2 factor is the result of the multiple moving measurements, which results in complex operations, time-consuming, and unable to realize the measurement for beam quality M2 factor of the transient laser system in real-time. Here, a novel real-time measurement of beam quality M2 factor based on self-referencing interferometer (SRI) is proposed, and the main contents are as follows: Firstly, according to the international standard, ISO11146, of the M2 factor measurement method, the theory model of measurement method for M2 factor, which with the basis of complex amplitude information of the measured laser beam, is established. Secondly, the real-time measurement experimental system for M2 factor based on SRI is built, the influence laws of pinhole diameter, magnification of the SRI, and the carrier frequency error on the measuring precision of the reconstruction complex amplitude and the M2 factor of laser beam, respectively, are revealed by using of the related theory analysis, numerical stimulations, and experimental studies with the SRI experimental system. Moreover, according to the correction results, the experimental measurement system for M2 factor are optimized and perfected. Finally, the feasibility of the M2 factor measurement method and the experimental system based on SRI are performed with experimental studies, in order to realize the transient laser beam quality factor M2 measurement in real-time. The objective of the study’s results is expected to provide theoretical foundations and technical supports for research fields in pulse laser or transient laser beam quality evaluation and application.

M2因子是衡量激光光束优劣的重要指标，它的评估与测量在应用激光领域具有重要意义。然而传统M2因子需要多次测量方可获得，不仅操作繁杂、耗时长，且无法用于瞬态激光光束质量的评价与测量。本项目拟发展一种基于自参考干涉(SRI)的M2因子实时测量方法，并对其关键技术作系统的理论与实验研究，主要内容如下：首先根据国际标准ISO11146规定的M2因子测量方法，建立以激光复振幅信息为基础的M2因子测量方法理论模型；其次搭建基于SRI的M2因子测量系统，利用理论分析、数值仿真与实验研究等手段揭示针孔直径、放大倍数S、去载频误差等关键因素对激光复振幅重建和M2因子测量精度的影响规律，实现对M2因子测量系统的完善与优化；最后实验研究M2因子测量方法与系统的可行性，实现对瞬态激光M2因子的实时测量。本项目的研究可望为脉冲激光或瞬态激光的光束质量评价与测量等研究领域提供相关理论基础与技术支持。

光束质量是评价激光应用中的一个极为关键的参数, 通常用它来评价激光输出光束的传输特性, 它对激光器的理论分析、设计、制造、检测、实际应用等方面具有重要意义。在综述了激光光束质量评价参数与测量方法的基础上，针对传统M2因子难以实现实时测量的难题。提出一种基于MZ-PDI波前传感器对激光光束质量实时测量方法，并给出相应的实验结果，具体包括：(1)提出Mach-Zehnder点衍射干涉(MZ-PDI)波前传感器及其复振幅重建方法。采用传统Mach-Zehnder径向剪切干涉仪的参考臂中设置一个针孔空间滤波器使之产生理想的参考光，同时在信号光与参考之间引入空间线性载频，使得新型的MZ-PDI无需专门的参考光、仅需单幅干涉条纹图(单次测量)，且无需任何迭代过程就可以快速准确地复原出待测波激光复振幅分布情况；提高了激光波前和强度分布的探测速度，可适用于各种静态或动态光场的复振幅重建与检测等应用领域。(2)提出基于MZ-PDI激光光束质量M2因子实时测量方法。从理论上分析了基于复振幅M2测量方法的可行性；然后给出了基于MZ-PDI法的激光光束质量M2测量系统的设计方案；最后对静态或动态多模激光光束质量进行实验研究。实验结果表明采用基于MZ-PDI的M2测量方法与传统的M2因子测量仪得到的结果基本一致，验证了所提方法的可行性与有效性。(3)针对传统M2因子在实际应用或测量时存在值不唯一的缺陷，提出采用M2-曲线评价非旋转对称激光光束的方法。首先给出了M2-曲线的理论分析与推导过程，再给出了基于MZ-PDI测量M2-曲线的基本原理，最后对DPSSL输出多混合模的激光光场进行实验研究。结果表明，采用M2-曲线能够很好的克服传统M2因子在评价非旋转对称光束上值不确定的问题，并且M2-曲线是一个更为客观、具有更为广泛物理意义的评价方法，为激光光束质量评价与测量提供一种参考依据。