High-Frequency Optically Heterodyned Saturation Spectroscopy Via Resonant Degenerate Four-Wave Mixing

Resonant degenerate four-wave mixing with two close optical frequencies (, +) is used to perform high-frequency optically heterodyned saturation spectroscopy. Doppler-free spectra of I₂ (=514. 5 nm) are obtained in this way for 20 kHz<<20 MHz. Lock-in detection for <1 MHz allows relaxation studies and line assignments. At higher frequencies, rf-power detection yields Doppler-free doublets split by 32.