Resonance Charge Transfer and Population Inversion FollowingC5+andC6+Interactions with Carbon Atoms in a Laser-Generated Plasma

Enhanced population of the $n=4\mathrm{}$ excited state is measured in both ${\mathrm{C}}^{4+}$ and ${\mathrm{C}}^{5+}$ ions in agreement with a theory for formation by resonance charge transfer between carbon ions and atoms. A background gas modifies and mixes the interacting particles originating from a carbon surface vaporized by a focused laser beam. Population inversions capable of producing quasi-cw amplification in the extreme ultraviolet region are measured.