$ 2.1概述一光腔理论的一般问题谐振腔的作用无源谐振腔理论依据开放式光腔开腔的分类无源谐振腔的模式光腔的损耗
§2.1 概述－光腔理论的一般问题 谐振腔的作用 无源谐振腔 理论依据 开放式光腔 开腔的分类 无源谐振腔的模式 光腔的损耗
. Laser cavities differ in several significant ways fromthe closed microwave cavities that are commonlytreated in electromagnetic theory textbooks.: Optical resonators first of all usually have open sidesand hence always have diffraction losses because ofenergy leaking out the sides of the resonator toinfinity.: Optical resonators are also usually described inscalar or quasi plane-wave terms, with emphasis onthe diffraction effects at apertures and mirrors edgesrather than in vector terms with emphasis onmatching boundary conditions. The distinction between “longitudinal"' and“transverse"' modes in the resonator is also muchsharper in optical than in microwave resonators
• Laser cavities differ in several significant ways from the closed microwave cavities that are commonly treated in electromagnetic theory textbooks. • Optical resonators first of all usually have open sides, and hence always have diffraction losses because of energy leaking out the sides of the resonator to infinity. • Optical resonators are also usually described in scalar or quasi plane-wave terms, with emphasis on the diffraction effects at apertures and mirrors edges, rather than in vector terms with emphasis on matching boundary conditions. • The distinction between “longitudinal” and “transverse” modes in the resonator is also much sharper in optical than in microwave resonators
一谐振腔的作用模式选择。保证激光器单模（或少数轴向模）振荡，从而提高激光器的相干性；控制腔内振荡光束的特性（直接控制光束的横向分布特性、光斑大小、谐振频率及光束发散角等），提供轴向光波模的反馈
一 谐振腔的作用 • 模式选择。保证激光器单模（或少数轴向 模）振荡，从而提高激光器的相干性； 控制腔内振荡光束的特性 （直接控制光束的横向分布特性、光斑大小、 谐振频率及光束发散角等） ◆ 提供轴向光波模的反馈
二无源谐振腔·不考虑腔内激活介质的影响无源腔模式可以作为具有激活介质腔（有源腔）的激光模式的良好近似·激活介质的作用主要是补充腔内电磁场在振荡过程中的能量损耗，使之满足阈值条件；激活介质对场的空间分布和振荡频率的影响是次要的，不会使模式发生本质的变化
二 无源谐振腔 • 不考虑腔内激活介质的影响 • 无源腔模式可以作为具有激活介质腔（有 源腔）的激光模式的良好近似 • 激活介质的作用主要是补充腔内电磁场在 振荡过程中的能量损耗，使之满足阈值条 件；激活介质对场的空间分布和振荡频率 的影响是次要的，不会使模式发生本质的 变化
采用的理论一·几何光学理论--推导腔的稳定性条件（不能得到腔的衍射损耗）·衍射光学理论--深入了解模式特性
三 采用的理论 • 几何光学理论-推导腔的稳定性条件（不能 得到腔的衍射损耗） • 衍射光学理论-深入了解模式特性