Abstract

We propose the generation of XUV and soft X-ray laser radiation by electronion recombination in capillary plasmas excited by fast discharges. Highly ionized plasmas are created in a capillary geometry by a high current pulse; subsequently rapid cooling of the plasma occurs by electron heat conduction and radiation. Electron-ion recombination is expected to result in population inversion and gain in 3-2 transitions of hydrogenic ions with wavelengths ranging from the VUV to soft X-rays. We have generated nearly completely ionized helium and lithium capillary plasmas to study the possibility of amplification in the 3-2 hydrogenic lines during plasma recombination. Time resolved XUV spectra of a 500 μm diameter lithium capillary discharge were obtained. The intensity of the LiIII 72.9 nm 3-2 line is observed to increase during the decay of the current pulse. The capillary discharge recombination scheme is expected to advantageously scale to soft X-rays wavelengths. A time dependent collisional-radiative model of the capillary plasmas predicts a gain of 5 cm⁻¹ in the 18.2 nm CVI transition.

© 1988 Optical Society of America