Experimental investigation of high-power single-pass Raman shifters in the ultraviolet with Nd:YAG and KrF lasers

Single-pass Raman cells pumped by either a quadrupled Nd:YAG (266-nm) laser or a KrF excimer laser are studied. The Raman-active gases comprise H-2, D-2, or CH4, as well as a mixture of them, with the addition of He, Ne, or Ar. A parametric study, in which the Stokes conversion efficiency and the beam quality (M-2) were measured, was made. The first Stokes efficiency increases and all the Stokes thresholds decrease with an increase in the lens focal length or the M-2 parameter of the pump beam. The quality of the Stokes beams deteriorates when the active-gas pressure increases but is improved by the addition of an inert gas. Laser-induced breakdown is shown to be a factor that limits the conversion efficiency and the quality of the Stokes beams. With a mixture of D-2, H-2, and Ar, a 10-15-mJ pulse energy is obtained (depending on the pump M-2 parameter) in the first Stokes beam of D-2 (289 nm) and H-2 (299 nm), with a full-angle divergence of 0.5 mrad (at 86% power). (C) 1997 Optical Society of America.