Observation of vibrational enhancement using pre-resonant infrared four wave mixing

A vibrational enhancement of the third order optical susceptibility (χ(3)) is found for the CH stretch of hexane using nonparametric infrared four wave mixing. Two tunable infrared beams and one visible laser were focused into hexane with deuterobenzene as an internal standard. The four wave mixing enhancement was measured for different frequencies in the preresonant region using the interference between a coherent Raman process in the deuterobenzene and the vibrationally enhanced nonparametric process from the hexane. The frequency dependence of the nonparametric process matches that expected for vibrational enhancement.