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

Resonant degenerate four-wave mixing with two close optical frequencies (ω, ω+δ) is used to perform high-frequency optically heterodyned saturation spectroscopy. Doppler-free spectra of I₂ (λ=514.5 nm) are obtained in this way for 20 kHz<δ<20 MHz. Lock-in detection for δ<1 MHz allows relaxation studies and line assignments. At higher frequencies, rf-power detection yields Doppler-free doublets split by 3δ2.