Traveling-wave excitation of the Ar II shake-up laser at 476.5 nm

We describe the construction and operation of a single-pass laser in Ar II at 476.5 nm pumped by soft x rays from a laser-produced plasma. Temporal and spatial coherence properties have been characterized by means of a variety of experimental techniques. We use a 5-J, 100-ps, 1053-nm laser pump pulse in a traveling-wave geometry to measure a maximum output energy of 550μ. The aspect ratio of the unsaturated gain region directly affects the divergence of the output laser beam, resulting in a half-angle divergence of 10 mrad for 10 cm of excitation length. A small-signal gain coefficient of 2.1 cm⁻¹ was observed, with the onset of saturation occurring after just 2 cm of excitation.