We point out that there is no oddness in the expression of the cross-spectral density of a partially coherent flat-topped beam given by Ge et al. [Appl. Opt. 43, 4732 (2004)]. The criticism of the comment by Wu et al. [Appl. Opt. 45, 366 (2006)] is not appropriate because no one has proved that the M~(2) factor as defined by them must be greater than or equal to 1. We propose a new definition of the M~(2) factor that really confines the propagation of partially coherent beams. The new definition leads to M~(2) > 1 for the partially coherent beam given by Ge et al.
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