二单元_光学谐振腔2节.ppt

* * 9 非稳定腔的共轭像点及几何自再现波形 任何非稳定腔的轴线上都存在一对共轭像点 ， ，从这一对共轭像点中任意一点发出的球面波在腔内往返一次后其球面波形保持不便，即能够实现自再现。 10 高斯模的匹配 需在合适的位置放置一个焦距适当的透镜，应使两束高斯光束互为物象共轭光束； 复习：开放式谐振腔与高斯高束 * * 模式、谐振腔及谐振腔与模式的关系 共轴球面腔的稳定性条件 自再现模的概念 共焦腔的自再现模式、行波场 高斯光束的性质、传输变换 一般稳定性球面腔的自再现模式、行波场 第二章概要 稳定谐振腔 非稳定谐振腔 非稳定谐振腔自再现模式 * 对于任意的将稳定腔，我们可以通过研究与其对应的共焦腔的特征模来研究它的模的性质。由于共焦腔的行波场是高斯光束，因此，高斯光束的性质对于稳定腔的行波场具有代表意义，因此我们来单独讨论高斯光束的主要性质。 F:高斯光束的焦参数由于有正负，因而R(z)也有符号，其符号意义为： 如果R0，则球面轴线上的半径方向为z正方向；如果R0，则为z负方向。 为高斯光束共焦参数 * In figure 7.2 the transverse electromagnetic laser modes were described. The most important mode is the basic transverse mode TEM00. When laser radiation is emitted in a single transverse mode, it is usually the basic transverse mode TEM00 (see section 4.3.3). Since the Gaussian curve decay to its sides in a non linear shape, it is difficult to determine its borders exactly. Thus, it is common to determine the Gaussian beam diameter as the distance along the cross section of the beam in which the intensity of the beam is 1/e2 (0.135) of its maximum intensity at the center of the beam. The area inside a circle with the beam diameter contains 86.5% of the energy (power) of the Gaussian beam. The rest 13.5% of the energy are outside this artificially determined diameter. There are other definitions for the Gaussian beam borders: The distance along the cross section of the beam in which the intensity of the beam is 1/e (0.368) of its maximum intensity at the center of the beam. With this definition 63% of the beam energy are inside the beam diameter circle. Points of half the maximum power. Any other percentage of the maximum power (85% or 90% are common). Attention ! When comparing data from different sources, the exact definition of beam diameter need to be compared. Sometimes the laser beam size is determined by the radius of the beam (distance from the center), which is half the number of the beam diameter defined earlier.  In Single basic transverse mode the radiation shape on a perpendicular