Stimulated rotational Raman conversion in H2, D2 , and HD

Stimulated rotational Raman conversion has been efficiently demonstrated in all three molecular hydrogen isotopes with a 532-nm Q-switched pump source. Optimum gas pressures and pump focusing have been determined. Single pass conversion efficiencies of 80%, 75%, and 65% have been achieved at the first Stokes wavelengths with H₂ , D₂, and HD, respectively. The maximum efficiency is generally limited by further Raman conversion of the initially generated Stokes light. The thresholds were found to increase in the order H₂ <D₂<HD as expected. With the 100 cm lens, the threshold for HD is ~8 times that for H₂. The relative thresholds of H₂ and D₂ are reasonably consistent with the calculated steady-state gains based on the population statistics and the linewidth data. Intermediate frequency shifts such as these may be useful by themselves, or in combination with other nonlinear techniques, as methods to achieve specific wavelengths for system applications