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讨论与M~2参数有关的一些问题。当采用光束二阶强度矩方法定义光束光斑大小和远场发散角时,M~2参数满足M~2≥1。但当改变其定义后,例如,采用86.5%(或其它百分比)功率通量法定义光束光斑大小和远场发散角时,由此定义的M~2参数(M_(pc)~2)的最小值是多少,什么样的光束具有最小的M~2参数(M_(pc)~2)。本文在采用86.5%(或其它百分比)功率通量法定义光束光斑大小和远场发散角的前提下,对这些问题进行了讨论。结果表明:共焦腔的输出光束应具有最小的M~2参数(M_(pc)~2);当采用86.5%功率通量法定义光束光斑大小和远场发散角时,M~2参数(M_(pc)~2)仍满足:M_(pc)~2≥1;但当采用其它百分比定义时,M~2参数(M_(pc)~2)有可能小于1,M_(pc)~2的大小取决于所定义的光斑半径内包含的光功率的百分数。
Discuss some issues related to M ~ 2 parameters. When using the beam second-order intensity moment method to define the beam spot size and far-field divergence angle, M ~ 2 parameters satisfy M ~ 2≥1. However, when the definition is changed, for example, when the beam spot size and the far-field divergence angle are defined by the power flow method of 86.5% (or other percentages), the minimum value of the M ~ 2 parameter (M pc2) What is the value and what kind of light beam has the smallest M ~ 2 parameter (M_ (pc) ~ 2). In this paper, we discuss the issues of beam spot size and far-field divergence angle using 86.5% (or other percentage) power flux method. The results show that the output beam of the confocal cavity should have the minimum M ~ 2 parameter (M_ (pc) ~ 2). When the beam spot size and far-field divergence angle are defined by 86.5% M_ (pc) ~ 2) still satisfy: M_ (pc) ~ 2≥1; However, when using other percentages, M ~ 2 parameter (M_ (pc) ~ 2) may be less than 1, The size depends on the percentage of optical power contained within the defined spot radius.