Starting from the space-time Wigner distribution function and taking the Gaussian Schell-model (GSM) pulsed beam as a typical example, the closed-form expressions for the M2 factor have been derived.

• 从时空维格纳分布函数出发,以高斯-谢尔(GSM)脉冲光束为例,导出部分相干超短脉冲光束的M2因子公式。