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

摘要

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 t 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↓(2) (299 nm), with a full-angle divergence of 0.5 mrad (at 86% power).#1997 Optical Society America