Molecular fluorine (f.sub.2) laser with narrow spectral linewidth

Abstract

A molecular fluorine (F.sub.2) laser is provided wherein the gas mixture comprises molecular fluorine for generating a spectral emission including two or three closely spaced lines around 157 nm. An etalon provides line selection such that the output beam only includes one of these lines. The etalon may also serve to outcouple the beam and/or narrow the selected line. Alternatively, a prism provides the line selection and the etalon narrows the selected line. The etalon may be a resonator reflector which also selects a line, while another element outcouples the beam. The etalon plates, preferably uncoated, comprise a material that is transparent at 157 nm, such as CaF.sub.2, MgF.sub.2, LiF.sub.2, BaF.sub.2, SrF.sub.2, quartz and fluorine doped quartz. The etalon plates are separated by spacers comprising a material having a low thermal expansion constant, such as invar, zerodur.RTM., ultra low expansion glass, and quartz. A gas such as helium or a solid such as CaF.sub.2 that does not absorb radiation 157 nm fills the gap between the etalon plates, or the gap is evacuated. The gas mixture preferably further includes neon as a buffer gas. Another etalon may be used for line narrowing. One or more of a highly reflective mirror, a high finesse etalon or a prism with a highly reflective back surface may serve as a highly reflective resonator reflector. Any of one or more etalons, a prism, a brewster plate and a highly or partially reflective mirror may seal the laser discharge chamber.