Observation of the population inversion of O VIII levels in a laser plasma

An experimental investigation was made of the optical properties of a plasma formed by irradiation of an Al₂O₃ target in vacuum with high-power neodymium-glass laser radiation. It was found that at some distance from the target surface the levels of hydrogen-like oxygen ions with the principal quantum numbers n = 2, 3, and 4 were inversely populated. The gain at the λ ~29 nm wavelength (4→3 transition) was ~0.1 cm^–1.