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 and HCD tubes with varying lengths of the cathode segments. The measurements are performed at 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 similar to 1 divided by 2 cm for IR and 2 divided by 5 cm for UV laser oscillation.