Studies of the time-delayed second-harmonic generation (TDSHG) from a monolayer of rhodamine 6G dye and retinal using an incoherent broadband source are reported. The method possesses both the submonolayer sensitivity and the surface specificity of second-harmonic generation and the ultrahigh temporal resolution of a broadband light source. Two exciting laser beams generated by the same broadband light are relatively delayed and then recombined on the monolayer surface in a noncollinear excitation geometry. The calculated intensity of the reflected SHG beam exhibits a dephasing-induced decay tail. Using a broadband fluorescence in 548 dye laser with a central wavelength at 546 nm and a correlation time of 112 fs, the time-delayed four-wave mixing (TDFM) signals from bulk samples and the TDSHG from monolayers were obtained. The retinal dephasing time of retinal appears to be shorter than that of rhodamine 6G dye even though the excitation wavelength is on the redtail of the retinal absorption band. No significant difference between the dephasing times of the molecules in the condensed phase and the monolayers is observed.