The underlying mechanism of the spectral cleaning effect of the cross-polarized wave (XPW) generation process was theoretically investigated.This study shows that the spectral noise of an input spectrum can be removed in the XPW generation process and that the spectral cleaning effect depends on the characteristics of the input pulses,such as the chirp and Fourier-transform-limited duration of the initial pulse,and the modulation amplitude and frequency of the spectral noise.Though these factors codetermine the output spectrum of the XPW generation process,the spectral cleaning effect is mainly affected by the initial pulse chirp.The smoothing of the spectrum in the XPW generation process leads to a significant enhancement of the coherent contrast.