对M^2参数极值问题的一些讨论

Some Discussion on the Extremum of M^2-Values

在采用86.5%功率通量法定义光束束宽和远场发散角的前提下,对由此定义的M^2参数M_(PC)~2的最小可能取值及具有最小M_(PC)~2参数的光束特性等问题进行了讨论。结果表明:共焦腔的自再现模应具有最小的M^2参数M_(PC)~2;当采用86.5%功率通量法定义光束束宽和远场发散角时,在近轴近似条件下,由具有同一中心的两基模高斯光束轴向叠加所形成的自再现光束,M_(PC)~2大于等于1。

When the real beam width and far-field divergence angle are defined by 86.50% power content values, the minimum of the defined M2 factor M^2PC and the characteristics of the beam with the smallest M^2PC are discussed initially in this pa per. The results indicate that the self-reproduction modes in confocal cavity possess the minimum of the Me factor M^2PC. When the real-beam width and far-field divergence angle are defined by 86.5% power content values, in paraxial approximation, among the self-reproductive beams formed by axial superpositon of two fundamental mode Gaussian beams with the same center, the M^2PC is not less than 1.