SUPPRESSION OF STIMULATED HYPER-RAMAN SCATTERING IN LITHIUM VAPOR

Abstract

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 excitation near the 2S-3S or the 2S-4S two-photon resonance is completely suppressed, but the SHRS associated with the 3P excitation near the 2S-4S two-photon resonance can be observed. A condition under which the forward SHRS takes place, given by Malakyan [3], has been examined. A reasonable agreement between the theory and the experiment is obtained. Near the 2S-3S two-photon resonance, instead of the expected emission omega2P-2S corresponding to the 2P-2S transition, an emission at the 2omega(P)-omega3S-2P frequency, which is close to the omega2P-2s, has been observed in the backward direction. The process generating this emission could be considered as an inverse SHRS process induced by the 3S-2P spontaneous emission. For the SHRS emission a shift of the observed frequency from the calculated frequency has been found. In order to explain the shift, the Stark effect has been calculated. The results show that the shift can not be attributed to the Stark effect.