激光光束传输因子M^2的一些问题

ON THE PROBLEMS OF THE BEAM PROPAGATION FACTOR M^2

本文讨论与 M2 因子有关的一些问题 ,指出在近轴近似条件下由光束的二阶强度矩定义的 M2 因子满足 M2 ≥ 1 ,其中只有对基模高斯光束等式才成立 .由光束的功率通量值定义的 M2 因子 ( M2pc)有可能小于 1 ,M2pc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 .通过计算光场的二阶矩 ,我们获得了轴向相干叠加的高斯光束的 M2

The problems concerning the M 2 factor are discussed.It is pointed out that M 2≥1 holds in paraxial approximation,if M 2 is defined by the second order intensity moments of the beam.The equality holds only for the fundamental Gaussian beam.The M 2 factor defined by the power content can be smaller than one,depending on the percentage of the enclosed power.By calculating the second order moments,the analytical solution of the M 2 factor of axially coherent superposition of Gaussian beams is obtained.