Intensity enhancement of the C5+ Balmer radiation excited by capillary discharge pumping

The intensity of the 18.2 nm Balmer alpha-transition in C5+ excited in a ca pillary discharge using alumina and polyacetal tubes was studied. For disch arge currents of up to 80 kA in tubes filled with C2H2, intense radiation f rom the excitation of C5+ ions and from the recombination of C6+ ions was o bserved. With increasing length of the discharge, the intensity in the fall ing edge of the recombination pulse rises faster than proportional. In cont rast to previous investigations, gain by stimulated emission is excluded. T he enhancement is ascribed to an optical guiding of the XUV radiation in th e dense plasma created by ablation from the tube walls.