Resonance-enhanced infrared four-wave mixing by infrared-active molecules

We suggest that high-efficiency frequency upconversion and downconversion can be achieved by four-wave mixing in media containing infrared-active molecules. The high-efficiency results from the relatively large vibrational matrix elements and small energy denominators. Numerical calculations are presented for generation of radiation at 2ω1+ω2 in HCl where 2ω1 is tuned to an electric-dipole-forbidden vibration-rotation transition. We also present some general considerations for four-wave mixing in molecular media.