Generation of far-infrared laser pulses in CH3I gas by stimulated Raman scattering resonantly enhanced at fundamental and overtone transitions

We report on the generation of far-infrared laser pulses by stimulated Raman scattering in CH3I gas. Applying a continuosly tunable high-pressure CO2 laser as pump source we obtained 38 laser lines, 35 of them new, in the spectral range from 12 to 27 cm−1. Resonantly enhanced Raman scattering occured at vibrational-rotational transitions of the ν6 fundamental as well as the 2ν3 overtone band. In our experiment the efficiency of the 2ν3 Raman transitions was found to be about three times higher than for the ν3 Raman transitions. From the temporal behavior of the CH3I Raman laser we conclude a bandwidth of about 200 MHz for the realized Raman gain region for both kinds of transitions. Our results are also discussed with respect to the properties of the other methylhalides CH3F, CH3Cl and CH3Br.