Time- and space-resolved optical Stark spectroscopy in the afterglow of laser-produced tin-droplet plasma

J. Scheers, R. Schupp, R. Meijer, W. Ubachs, R. Hoekstra, O. O. Versolato

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

The afterglow emission from Nd:YAG-laser-produced microdroplet-tin plasma is investigated, with a focus on analyzing Stark effect phenomena and the dynamical evolution of the plasma. Time- and space-resolved optical imaging spectroscopy is performed on 11 lines from Sn i-iv ions, in the 315-425-nm wavelength range. Stark shift-to-width ratios serve as the basis for unambiguous experimental tests of atomic physics theory predictions. Experiment and theory, where available, are found to be in poor agreement, and are in disagreement regarding the sign of the ratio in several cases. Spectroscopic measurements of the Stark widths in tandem with Saha-Boltzmann fits to Sn i and Sn ii lines, establish the evolution of the local temperature and density of the plasma afterglow, 20-40 ns after the end of the 15-ns-long temporally box-shaped laser pulse. A clear cool-down from ∼2 to 1 eV is observed of the plasma in this time window, having started at ∼30 eV when emitting extreme-ultraviolet (EUV) light. An exponential reduction of the density of the plasma from ∼10^{18}-10^{17}e^{-} cm^{-3} is observed in this same time window. Our work is relevant for understanding the dynamics of the decaying, expanding plasma in state-of-the-art EUV nanolithography machines.

Original languageEnglish
Article number013204
Pages (from-to)1-9
Number of pages9
JournalPhysical review E
Volume102
Issue number1
Early online date9 Jul 2020
DOIs
Publication statusPublished - Jul 2020

Funding

This work was carried out at the Advanced Research Center for Nanolithography, a public-private partnership between the University of Amsterdam, the Vrije Universiteit Amsterdam, the Netherlands Organization for Scientific Research (NWO), and the semiconductor equipment manufacturer ASML. This project received funding from the European Research Council (ERC) Starting Grant No. 802648 and is part of the VIDI research program with Project No. 15697, which is financed by NWO.

FundersFunder number
Horizon 2020 Framework Programme802648
European Research Council15697
Nederlandse Organisatie voor Wetenschappelijk Onderzoek

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