SUPPRESSION OF STIMULATED HYPER-RAMAN SCATTERING IN LITHIUM VAPOR

The stimulated hyper-Raman scattering (SHRS) in lithium vapor has been observed in both the forward and the backward directions as the laser was tuned near the 2S-3S and 2S-4S two-photon resonances. It is found that in the forward direction the SHRS associated with the 2P excitat ion near the 2S-3S or the 2S-4S two-photon resonance is completely sup pressed, but the SHRS associated with the 3P excitation near the 2S-4S two-photon resonance can be observed. A condition under which the for ward SHRS takes place, given by Malakyan [3], has been examined. A rea sonable agreement between the theory and the experiment is obtained. N ear the 2S-3S two-photon resonance, instead of the expected emission o mega2P-2S corresponding to the 2P-2S transition, an emission at the 2o mega(P)-omega3S-2P frequency, which is close to the omega2P-2s, has be en observed in the backward direction. The process generating this emi ssion could be considered as an inverse SHRS process induced by the 3S -2P spontaneous emission. For the SHRS emission a shift of the observe d frequency from the calculated frequency has been found. In order to explain the shift, the Stark effect has been calculated. The results s how that the shift can not be attributed to the Stark effect.