Four-wave mixing with dynamic Stark effects in flames

Four-wave mixing is studied in a Na-seeded flame in the regime of strong saturation of the Na D-line transitions. The output frequency differs from that of the input lasers so that spectral discrimination can distinguish the mixing signal. Scans of the D2 resonance with another laser set at the D1-line resonance reveals two resonances corresponding to the D2 resonance and the frequency difference of the D levels. The mixing efficiency at the D2 resonance increases with the detuning of the D1 resonance. The frequency difference resonance is weak because of interference between multiple coherent pathways.