Excitation of levels of the O VII oxygen ion in a helium atmosphere

Measurements were made of the ratio of the intensities of resonant lines of helium-like oxygen ions as a function of the distance from the target surface under conditions of expansion of a laser plasma into vacuum and helium. A comparison between the experimental data indicated that additional excitation of the O VII levels is recorded when the plasma expands into helium. The results are interpreted on the basis of charge transfer between oxygen H-like ions and excited helium ions.