Dependence of laser power and gain on the cathode length of a sputtering copper ion laser

The dependence of the laser output power and the small signal gain for the 780.8 nm copper ion transition as a function of the cathode segments length in a sputtering longitudinal hollow cathode discharge are measured. The optimal cathode length in regard of maximum laser power is determined. From one and the same active volume at equal input power a considerable increase of laser output power is observed using the optimal length cathode segments. The results are in good agreement with the previously performed calculations and measurements of axial current and plasma characteristics, showing that the plasma is most intense near the anode ends of the cathodes. The measurements confirm that the highest laser power and excitation efficiency is achieved when the laser active volume comprises a series of anodes and cathodes, each cathode 2 cm long. This report is a part of a series of investigations aimed at optimization of the longitudinal hollow cathode discharge used as excitation medium of cathode sputtered metal ion lasers.