Nonresonant stimulated anti-Stokes Raman scattering from an inverted population in atomic iodine has been observed. The population inversion was achieved by flash photolysis of trifluoromethyliodide. A gain of
e7 was measured for a laser probe pulse at the anti-Stokes wavelength passing through the inverted iodine coincident with a laser pump pulse. This result is in good agreement with theoretical predictions.
The cross section for anti-Stokes Raman scattering from inverted atomic iodine is calculated by a semiempirical procedure and shown to be dominated by the quadrupole component. Relative intensities for ${F}_{2}\ensuremath{-}{F}_{1}$ transitions
F2 and
F1 are the total angular momenta of the initial and final hyperfine split states) in the hyperfine split multiplets are calculated, and maximal intensity of 25% is found for the 2-4 transition. However, in stimulated Raman scattering maximal gain is expected at the position of the 3-2 line, where collisional broadening and Stark splitting lead to a strong overlap of three lines. The resulting effective cross section is about 33% of the total cross section. For scattering with pump radiation at $\ensuremath{\lambda}=1.06$ \ensuremath{\mu}m an effective cross section of $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}=0.71\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}28}$
cm2 is obtained, with an estimated accuracy of 20%. This is somewhat lower than the estimate $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}={10}^{\ensuremath{-}28}$
cm2 which has been published recently.