Gas laser with sputter-resistant cathode

In a gaseous laser device comprising an envelope, a cathode volume, an anode volume, a cathode electrode within said cathode volume and formed as a thin adherent conductive metal film on the walls of said envelope bounding said cathode volume, a lasing gaseous volume, a cathode channel connecting said cathode volume to said lasing gaseous volume, an anode within said anode volume, and means for igniting a gaseous discharge between the anode and cathode and wherein the cathode has a relatively large area and at least one edge adjacent to said cathode connecting channel which is subject to gas discharge deterioration, the improvement wherein said at least one edge of said relatively large area cathode adjacent said cathode connecting channel has an insulating coating applied only on the said edge thereof and from about 0.1 micron to about 50 microns in thickness to protect the cathode from edge deterioration due to gas discharge without diminishing the effective surface area of said cathode and without increasing the average current density over said effective surface area.