The performance of the UV Cu+ laser in a slotted hollow cathode has been investigated experimentally. The laser power dependent on discharge current, neon pressure, cathode length, and laser mirror transmission has been measured. The optimum neon pressure was found to be 13 mbar. Single-pass gains about 8 percent . m-1have been evaluated. The observed changes in the slot shape by sputtering during 100 h of operation are briefly discussed. The experimental results are compared to a recent sputtering theory and reasonable agreement is found. The sputtering theory, the spontaneous intensity measurements, and the evaluated gains are used to calculate the number densities of the5sCu+ levels. Laser power is calculated from single-pass gains and agreement with experimental results is obtained.