Investigation of the spatial profile of stimulated Raman scattering beams in D2 and H2 gases using a pulsed Nd:YAG laser at 266 nm

The stimulated Raman scattering (SRS) beam spatial mode structure is studied in H-2 and D-2 gases, in a 60 cm-long high-pressure Raman cell, using a pulsed Nd:YAG laser at 266 nm. The conversion efficiencies of the first and second Stokes in H-2, D-2 and H-2/D-2 mixtures have been measured precisely in the 1-14 atm range. The SRS beam profiles were recorded for different gas pressures in the high-pressure Raman cell and interesting behaviour is revealed. Homogeneous SRS spatial profiles were obtained only for pressures higher than 7 atm. For lower pressures the profiles are either in the form of a ring or of a more complicated shape. The results are explained in terms of nonlinear self-focusing processes during the pump beam propagation in the Raman cell. Also, from our measurements, a more precise value of the nonlinear index of refraction for the H-2 and D-2 at 266 nm is proposed.