Calculated signal peak intensities at frequency of ω 2 as a function of the frequency ratios of two-color probe lasers with (a) different FWHMs (30 fs, 40 fs, and 50 fs) and same fundamental probe lasers (800 nm). (b) Same FWHM (50 fs) and different fundamental probe lasers (1200 nm and 1600 nm). Insets: amplified curves around the frequency rates ω 2 / ω 1 = 3.5 and 6. (c)–(e) Calculated signal peak intensities at frequency of ω 2 versus three series of frequency ratios ω 2 / ω 1 = 2 n , n+1/2, and n ± 1 / 3 with the same FWHM (50 fs) and different fundamental probe lasers (800 nm, 1200 nm, and 1600 nm).