高斯光束在单轴晶体中的布拉格衍射特性

Bragg Diffraction of a Gaussian Beam in a Uniaxial Crystal

利用适当的坐标变换和黎曼方法建立了高斯光束在单轴晶体中布拉格衍射的严格的耦合波理论 ,获得了一组严格的耦合波方程和衍射效率计算公式 ,讨论了衍射效率随折射率调制量的关系以及波长选择性和角度选择性 ,同时分析了衍射效率对再现光宽度的要求。模拟计算表明 ,异常光与异常光 (ee)型布拉格衍射能够达到的最大衍射效率由记录时入射角决定 ,而且通过各参量的适当的选择 ,理论上ee型布拉格衍射能够在折射率调制量很低(如 8.2× 10 -5)的情况下获得接近 90 %的衍射效率。

A rigorous coupled wave theory for the Bragg diffraction of a Gaussian beam in the uniaxial crystal is derived and a group of rigorous coupled wave equations and diffraction efficiency formula are obtained in terms of the proper coordinate transformation and Riemann method. The relations between the efficiency and the index modulation, the wavelength selectivity and the angular selectivity are discussed. At the same time, the requirement of the efficiency on width of the reconstruction beams is also analyzed. Simulation calculations show that, for the extraordinary to extraordinary (ee) Bragg diffraction, the possible maximum efficiency is determined by the incident angle of the recording beams. Moreover, by choosing every parameter properly, the theoretical efficiency can reach approximately 90% in the very low index modulation such as 8.2×10 -5 for ee type Bragg diffraction. This model may give a theoretic guidance for how to obtain high efficiency in the low index modulation condition.