Observation of new tunable ultraviolet radiation by four-wave mixing involving forbidden transitions in sodium vapor

We have observed four-wave mixing processes in sodium vapor in which the fourth wave is resonantly enhanced by the 4 s-3 s forbidden transition. Intense, tunable, coherent ultraviolet radiation has been observed near 383 and 388 nm with a tuning range of 50 and 20 Å, respectively. The sodium atoms are pumped by a single laser beam with wavelength in the 597 nm region. The third infrared wave involved in the mixing processes comes from either an OPSE or an output from another 4-WM process which is generated in the same sodium medium by the excitation of the same pump wave. The conversion efficiency is estimated to be 8 × 10 ^-4.