Effect of cathode length on the excitation efficiency of sputtering hollow cathode metal vapour lasers

The plasma in the hollow cathode discharge exhibits well-expressed axial inhomogeneity at dimensions typical for laser oscillation, which may affect the operation of the laser. To optimise the cathode dimensions for a sputtering metal vapour laser, we have measured the axial variation of cathode current and emission intensity of a number of He, Ne, Cu and Ar atom and ion lines, at different discharge conditions optimal for laser oscillation in He(He&Ar)-Cu and in Ne-Cu discharges. The observed axial excitation profiles are compared and the length of the cathode segments at which a nearly uniform discharge can be expected in He(He&Ar)-Cu and in Ne-Cu discharge is determined. Based on the results of the experiments we have demonstrated that the most efficient laser oscillation can be achieved when the laser active volume comprises a series of anodes and cathodes, each cathode with a length of ~1÷2 cm for IR and 2÷5 cm for UV laser oscillation.