通过分析光束远场发散角的二阶矩定义的局限性,讨论普遍情形下远场发散角的定义方法,提出并举例论证了“M2因子本质上是光束准直性的量度,在介质中传输的光束当非线性效应不可忽略时其光束质量M2因子不受M2≥1判据限制”的观点,重申了M2≥1与量子力学测不准原理在物理内容上的无关性。

By analysing the limitation of the second moment definition of divergence angle and redefining this angle which is related to the beam width, we pointed out that the quality factor M2 is essentially a measure of the beam collimation. Taking the nonlinear self focusing optics phenomenon as an example, we illustrated that this factor could be smaller than one if the possible nonlinear effects become important. The discrepancy between the inequality M2≥1 in linear optics and the uncertainty relation of quantum mechanics was also emphasized.