基于时空耦合的宽谱激光的光束质量表征

The broadband spectral laser has wide application prospects in fields of.Information, Biomedicine and Industry, etc. Nowadays, Broadband spectral laser’s short propagation distance and poor beam quality are bottlenecks which restrict the improvement of its performance. Therefore, it is of great significance to the improvement of its beam quality both in scientific research and application fields. In the programme, special attention has been paid on the key factors which influence the broadband spectral beam’s beam quality. Starting from Maxwell’s Equations, the spatio-temporal coupling field profiles of the two-wavelengths and multi-wavelengths lasers have been derived analytically; the theoretical model to analyze their beam quality has been presented, and the influences of the coherence in the space-time domain on the beam quality have been studied. Based on the theory of spatio-temporal coupling, combining with the nonlinear SchrÖdinger Equation,the mode or field distribution of the broadband spectral laser related to the spectrum coherence has been illustrated; the corresponding theoretical model for beam propagation and beam quality has been built, the factors and mechanisms which have impact on the beam quality have been discussed. Special attention has been paid on the propagation of the supercontinuum in different media as well as in the atmosphere and the corresponding beam quality. The influences of the parameters of the pumping source, the nonlinear fiber, the coherence between different spectra in the supercontinuum and the characteristics of the atmosphere, on its beam quality have been carried out. Beam quality measurement setup is constructed and optimized for practical application, the beam quality is analyzed experimentally . The results can be used to verify and meliorate the corresponding theoretical model, and it can help with the improvement of the broadband spectral laser beam quality.

宽谱激光在信息、生物医学和工业等领域有着广泛的应用前景。目前，宽谱激光源的传输距离不远、光束质量较差已成为制约其性能提升的瓶颈，因此对宽谱激光光束质量的提高的研究具有重要的学术价值和应用价值。本项目针对影响宽谱激光光束质量的关键问题展开研究：从麦克斯韦方程组出发，解析推导出双波长、多波长部分相干光的时空耦合场分布，建立其光束质量分析模型，研究时空相干性对其光束质量的影响；基于时空耦合理论，结合非线性薛定谔方程，给出与光谱相干性相关的宽谱激光的模式/场分布，建立宽谱激光传输和光束质量表征的理论模型，探索影响其光束质量的因素和机理，着重分析超连续谱激光在不同介质和大气中的传输演化及光束质量；讨论泵浦源参数、非线性光纤参数、光谱间的相干性和大气特性参数等对其光束质量的影响。搭建和优化可实用化的宽谱激光光束质量测量装置，实验研究其光束质量，验证和完善相应的理论模型，为提高宽谱激光光束质量提供指导。

宽谱光源的光束质量问题已成为制约其性能提升及应用的瓶颈之一，因此对宽谱的光束质量的研究具有重要的学术价值和应用价值。我们针对影响超连续谱激光光束质量的关键问题开展了理论和实验研究，取得以下成果：从PCF光纤特性、泵浦源特性、非线性效应以及光纤模式特性等方面研究了其对超连续谱输出光谱、相干性、传输特性和光束质量的影响。提出了光谱平坦度参数(Spectral Flatness Measure，简称SFM)用于表征超连续谱(SC谱)激光的平坦性。建立和完善宽谱激光传输和光束质量表征的理论模型，研究了液体填充的多芯光子晶体光纤、色散可控三角形晶格周期排列的正六边形结构的光子晶体光纤、新型高非线性光纤中超连续谱的产生机理和基于2μm脉冲激光泵浦产生的中红外超连续谱；研究了高相干度超连续谱的产生、控制、相干性及其传输特性；搭建了皮秒脉冲泵浦PCF产生SC谱的实验装置，并开展了初步实验工作，分析了泵浦参数以及光纤结构对产生SC谱的输出功率和输出光谱的影响；搭建了用于测量激光及超连续谱光束质量测量的实验装置。研究结果可用于系统地分析影响输出光谱范围、光谱平坦性、相干性以及光束质量的关键因素和主要物理机制，将为超连续谱激光性能的优化奠定基础。