A helium purge for a grating based line narrowing device for minimizing thermal distortions in line narrowed lasers producing high energy laser beams at high repetition rates. Applicants have shown substantial improvement in performance with the use of helium purge as compared to prior art nitrogen purges. In preferred embodiments a stream of helium gas is directed across the face of the grating. In other embodiments the purge gas pressure is reduced to reduce the optical effects of the hot gas layer.
This invention relates to lasers and in particular to high power gas discharge lasers with a grating based line narrowing unit. This invention is a continuation of Ser. No. 09/716,041, filed Nov. 17, 2000 now U.S. Pat. No. 6,778,584 which is a continuation-in-part of Ser. No. 09/451,407, filed Nov. 30, 1999 now U.S. Pat. No. 6,735,236.
