Reply to comment on "Partially coherent flat-topped beam and its propagation"

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.