Cascaded four-wave mixing in transparent bulk media

Cascaded four-wave mixing was theoretically and experimentally studied in transparent bulk media. The obtained sidebands show small angle dispersion, but have good beam quality with M2 factor better than 1.1 in the measurement. The center wavelength of the generated multicolor sideband can be conveniently tuned by replacing the nonlinear medium with one of several different materials. Theoretical analysis and calculation based on the phase-matching condition with the consideration of broadband spectra of the two incident pulses clarified the mechanism of this process. Self-compressed multicolor 20-fs pulses, which were nearly transform-limited, were obtained when one of the two input beams was appropriately negatively chirped and the other was positively chirped.