Observation of anti-Stokes-stimulated Raman scattering and two-photon emission in lithium and sodium vapors

We have observed anti‐Stokes‐stimulated Raman scattering (ASRS) and two‐photon emission (TPE) in Li and Na metal vapors. We found that the TPE can be generated from most of the excited even−parity states of both atoms but not ASRS. In the present work, the ‘‘pump laser lines’’ which stimulate the ASRS and TPE are those optically‐pumped stimulated emissions (OPSE) generated in the same alkali metal vapor. Since ASRS and TPE processes take place from the same metastable state, strong competitions between both processes are expected. Enhanced outputs due to the presence of a resonant intermediate state in the ASRS and TPE processes have also been observed.