Optical Gain at 185 nm in a Laser Ablated, Inner-Shell Photoionization- Pumped Indium Plasma.

Inner-shell photoionization of In sup + ground state ions by a laser-produced plasma broad-band soft X-ray pump source has created a population inversion on the 185 nm 4d sup 9 5s sup 2 D sub (5/2) -> 4d sup 10 5p sup 2 P degrees sub (3/2) Transition in In sup (++). A small signal intensity gain of exp(0.38) was measured in a ~4mm path length yielding a gain coefficient of proportional to ~0.95 cm sup (-1). The initial population of ~10 sup 16 cm sup(-3) In sup + ground state ions is prepared by ablating a liquid indium target with a 10 nsec, 100 millijoule (mJ), 532 nm laser pulse yielding a highly ionized indium plasma.