XUV photoabsorption studies along extended isoelectronic sequences using a dual laser produced plasma techniques

Abstract

Hot dense plasmas produced when the output of powerful pulsed laser systems are focused onto targets located in vacuum have been the subject of extensive study for a number of years. Such plasmas have found applications both as intense sources of continuum radiation in the XUV and as a versatile source of ionic species. In the work reported here the above properties of the laser produced plasma were exploited and enabled many new photoabsorption spectra of ionic species to be recorded in the XUV region. Using a dual laser produced plasma technique the XUV radiation emitted from laser plasmas created on the surface of a high Z material was used to backlight a second laser plasma and carry out ionic photoabsorption studies at wavelengths below 300A. An extensive examination of a number of isoelectronic sequences was undertaken. XUV photoabsorption studies were carried out on members of the neon, sodium, argon, krypton, bromine, selenium and xenon sequences. Absorption along the neon like sequence was extended to the fifth member, Si V. We report here the first unambiguous photoabsorption spectrum of the neon like A1 ion showing the principal outer shell transitions together with 2s inner shell autoionizing features. Detailed XUV photoabsorption spectra of the Si4+ ion are reported here for the first time, excitations involving an inner 2s electron were classified and m the case of the 2s-»3p transition found to be an example of forced autoionization. An intensity anomaly in the Beutler Fano line shape of the 2s->3p member of the autoionizing series 4 in Si was studied with varying plasma conditions. Absorption studies along the sodium isoelectronic sequence have resulted in the classification of new lines arising from transitions to core excited autoionizing 2 3 levels in the A1 and Si ions, transitions from ground and excited states were observed. XUV photoabsorption spectra of plasmas formed on targets of elements following argon (scandium and titanium) in the periodic table were found to be of a complex nature and to contain contributions from a number of different ion stages. Elements following krypton were also studied. Absorption spectra of laser produced plasmas formed on targets of strontium, yttrium and zirconium were recorded. The strontium and yttrium work resulted m 3d->4p transitions being observed m a number of ion stages for the first time. Work along the xenon sequence was found to be in 2 agreement with previous Ba observations Absorption studies along the sequence were extended to the fifth member Ce4+. An extensive analysis of the 4d photoabsorption spectrum of La was carried out and revealed that the 4d-»4f transition, expected to be the strongest was not observed. The interpretation of the spectrum showed that the feature possessed a large autoionization width and was not present m the experimental spectrum. The analysis further confirmed 2 that the 4f wave function m Ba is only partially collapsed. The work reported here has clearly shown the dual laser produced plasma technique to be a powerful and versatile method for recording XUV photoabsorption spectra of ionized species