Laser-induced resonances in the continuum observed in optical frequency mixing in sodium vapor

Frequency mixing in sodium vapor was observed when the sum frequency was tuned near a laser-induced autoionization-like resonance. The energy characteristics of phase-matched conversion by a two-photon transition were optimized. The efficiencies of the various processes were determined under different experimental conditions. Saturation of the mixing signal on increase in the incident power was observed experimentally for the first time.