Observation of saturation dip in degenerate four-wave mixing and two-color resonant four-wave mixing spectra of jet-cooled CH

We report both degenerate four-wave mixing (DFWM) and two-color resonant four-wave mixing (TC-RFWM) spectra of jet-cooled CH produced from photolysis of CHBr3 at 248 nm. A vibrational temperature 3400±200 K is determined for CH, in agreement with measurements of laser-induced fluorescence. Line splitting with a dip at the center due to saturation is observed at total laser energies greater than 100 μJ in both DFWM and TC-RFWM; it is more readily observed with the all-parallel YYYY polarization scheme than in other polarization arrangements. Possible models for the saturation dip are discussed.