Parametric study of a high-voltage hollow-cathode infrared copper-ion laser

Abstract

A new, segmented-electrode, high-voltage, hollow-cathode, Cu II laser, operating on the 780.8 and 782.5 nm transitions, is studied. Parametric measurements are presented for the discharge voltage, the spatially averaged copper-atom concentration and, for the two transitions, the small-signal gain coefficient, the laser threshold current and the laser output power. The dependence of the laser output power on the active length, the buffer-gas pressure and the transmission of the output coupler is modelled using equations for a low-loss, homogeneously broadened, standing-wave laser. For the 780.8 nm line, the lowest threshold current is 0.19 A for a 5 cm active length and a 0.1% transmission output coupler, and the maximum output power is 58 mW for a 3 A discharge current, a 7.5 cm active length and a 2% transmission output coupler. This performance exceeds that of conventional hollow-cathode lasers on the same transition, the improvement being attributed to the increased operating voltage, which gives a more efficient pumping discharge by simultaneously raising the ground-state copper-atom concentration (through the increased sputtering yield of ions bombarding the cathode) and increasing the efficiency of ionization.