Two-photon resonant four-wave mixing in atomic sodium vapour

Using the 4d- and 5s-states of sodium, two different types of two-photon resonance enhanced four-wave mixing have been observed. In the first type 2v _L =v _IR +v _pIR radiation near 2.34 μm and UV radiation near 320 nm has been detected. In the second typev _P −v _S =v _L +v _IR the UV radiation produced in the first parametric process acted as a pump for stimulated electronic Raman scattering via the 4p-state of sodium. Resonantly enhanced by the two-photon transition 3s–4s, radiation near 1.18 μm was produced in this scheme. The realisation of a tunable coherent IR source based on these four-wave mixing processes is discussed.