Raman shifting in the absence of multiple Stokes orders with a Nd:YAG laser in hydrogen: evidence of coupling between the forward and backward Stokes processes

By Raman shifting the output of a 1.319-/spl mu/m Nd:YAG laser in hydrogen, up to 24.5 mJ of Stokes light at 2.918 /spl mu/m has been generated. Due to the low energy of the 2.918-/spl mu/m Stokes photons, the first Stokes is the only Stokes line for this system. The effect of pressure on the conversion is notably simpler in this regime, but the gain saturates unusually slowly. An unexpected pump linewidth sensitivity in the forward Stokes conversion is observed. Coupling of the forward and backward Stokes processes is suggested as an explanation for these effects and is supported by a simple model.