Rapid differential decay of metastable populations in a copper halide laser

The time dependences of the populations ofthe copper metastable levels (²D_{$\text{5}\text{2}$}, ²D_{$\text{3}\text{2}$} have been measured in a longitudinally-excited CuBr laser of tube diameter 12 mm at a dissociation energy density of 15 mJ cm^-3. The metastable populations are created within 3 μs of the dissociation discharge pulse and thereafter decay to the ground level by electron collisions. The decay of the ²D_{$\text{3}\text{2}$} population is faster than that of the ²D_{$\text{5}\text{2}$} population and, in the case of CuBr, both decay rates are increased significantly by the decomposition products which arise from the presence of cupric oxybromide as an impurity. Decay times for the ²D_{$\text{5}\text{2}$}, ²D_{$\text{3}\text{2}$} populations as short as 4, 1.8 μs respectively have been observed under optimum laser conditions. The increase in the relative intensity of the 578.2 nm line at the shortest interpulse delays (ca 10 μs) is due to the more rapid decay of the ²D_{$\text{3}\text{2}$} population. At times up to the several microseconds after the dissociation current pulse the gas in the laser tube remains highly conducting. The rise-time of the pumping pulse is then determined by the external circuit rather than by the transit time of an ionization wave. The controlled effect of the cupric oxyhalide impurity in both CuBr and CuCl lasers offers the prospect of more efficient operation of copper halide lasers at repetition rates in excess of 20 kHz.