Optical frequency down conversion in caesium vapour

Experiments are reported in which a pulsed blue-dye laser beam ( omega L) was focused into a heat-pipe oven containing caesium vapour at densities of about 1023 cm-3. Tunable stimulated electronic Raman scattered infra-red radiation ( omega s) was observed together with radiation in the red region of the visible spectrum produced by optical frequency four-wave down conversion: omega R= omega L-2 omega s. Studies of the angular divergence and power of the red output beam demonstrate the importance of non-collinear phase matching in this process.