Laser-produced continua for studies in the XUV

摘要

Abstract: The spectrum of a laser-produced plasma in the XUV-VUV region consists typically of many strong emission lines together with varying degrees of continuum, the latter being due primarily to recombination. In plasmas produced by a Q-switched ruby laser (approximately 1 J output in approximately 25 ns) on a range of high Z targets, in particular the rare earth metals, it was found that the spectrum, over a wide wavelength region, consisted of smooth continuum with apparently no individual lines. The spectrum of samarium, for example, consisted of continuum from approximately 200 to 4 nm with no evidence of lines (except occasional impurity lines, due usually to oxygen). For ytterbium a similar clean continuum extended from 60 to 4 nm (the limit of the authors observations). The dominant stages of ionization in the plasmas are A$+10$PLU$/ to A$+15$PLU$/, and the observed absence of lines can be explained by a consideration of the electron configurations in these stages. The continua are very useful for experiments such as absorption spectroscopy and other applications in the XUV-VUV region and offer an alternative to the synchrotron when polarized radiation is not required. The sources are simple to mount and operate, are reproducible, intense, and insensitive to ambient pressure. Because of their pulsed mode of operation they are particularly suitable for time-resolved studies. Several applications of the sources are described and some possible future developments are suggested, including the use of excimer lasers.!