Photoionization-pumped gain at 185 nm in a laser-ablated indium plasma
We reportwhat is to our knowledge the first production of gain by inner-shell photoionization of ions. Photoionization of 4d electrons from In$+$ ions created a population inversion on a 185-nm In2$+$ transition. This scheme is an isoelectronic scaling of the 442-nm Cd$+$ laser. A single-pass gain constant of 0.9 {\textpm} 0.3 cm{\textminus}1 over a 0.4-cm path was pumped by soft x rays generated