Ultraviolet laser action from Cu II in the 2500-Å region

We have obtained cw laser action from Cu II at 2486, 2506, 2591, and 2599 Å by exciting a neon discharge in a copper hollow cathode. We have observed 7-mW cw output power just above threshold and the output appears to saturate at 210 mW under quasi-cw operation. The four ultraviolet laser lines observed originate from the 3d95s (3D) term of Cu II. The quantum efficiency of the 2500-Å laser transitions approaches 25%. Each of the four Cu II laser transitions has been employed in the past by spectroscopists as a secondary wavelength standard in the ultraviolet.