The He/Cl2 laser at 258 nm

A longitudinal pumping geometry was used to study lasing from e-beam pumped helium-chlorine mixtures at 258 nm. All measurements were performed with a maximum electron energy of 1.75 MeV and a beam current in the tube of 2.4 kA, beyond which little extra power was achieved. Time dependence, output powers and energies as well as the spectral composition of the laser pulses were determined for different experimental conditions. The one-mirror version yields the maximum extractable energy and power, 200 mJ and 6 MW respectively at optimum conditions, limited by saturation and absorption by excited states. Optical gain was observed for eight transitions around 258 nm. The fine structure results from isotopic splitting and contributions from different vibrational states. No bottle-necking occurs. A kinetic model reproducing the larger number of experimental data is proposed.