Selective population of the n=3 OVIII level during the expansion of a laser plasma in helium

The experimental use of a charge-exchange mechanism to form a population inversion in the levels of multiply charged ions, which may help lead to the development of sources of electromagnetic radiation in the far ultraviolet, is reported. During the expansion of a laser plasma burst containing multiply charged oxygen ions into a helium atmosphere, O VIII levels were selectively populated as a result of charge exchange of oxygen nuclei with helium ions. Results on the observed intensities of the O VIII resonant lines and on the effective cross sections for the charge exchanges are shown.