RESUMO
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 CH(4), 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).
