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Charge-state-resolved kinetic energy spectra of Sn ions ejected from a laser-produced plasma (LPP) of Sn have been measured at different densities of the H2 buffer gas surrounding a micro-droplet LPP. In the absence of H2, energetic keV Sn ions with charge states ranging from 4+ to 8+ are measured. For the H2 densities used in the experiments no appreciable stopping or energy loss of the ions is observed. However, electron capture by Sn ions from H2 results in a rapid shift towards lower charge states. At the highest H2 pressure of 6×10−4 mbar, only Sn2+ and Sn+ ions are measured. The occurrence of Sn+ ions is remarkable due to the endothermic nature of electron capture by Sn2+ ions from H2. To explain the production of keV Sn+ ions, it is proposed that their generation is due to electron capture by metastable Sn2+∗ ions. The gateway role of metastable Sn2+∗ is underpinned by model simulations using atomic collision cross sections to track the charge states of Sn ions while traversing the H2 buffer gas.

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Synopsis We report the absence of single-scattering peaks in collisions of tin ions on Mo and Ru targets. For these systems standard simulation packages as e.g. SRIM predict prominent single-scattering peaks. To identify the potential cause of the single-scattering peak missing, we changed charge state, energy, and species of the projectiles, detected ions and neutrals separately and studied collisions of Kr on Cu which has a similar mass ratio of projectie and target particles.

Rai, S. (2023). Ionic interactions around EUV generating tin plasma. [Thesis fully internal (DIV),

Synopsis Highly charged tin ions are the sources of extreme ultraviolet (EUV) light at 13.5-nm wavelength in laser-produced transient plasmas for next-generation nanolithography. Generating this EUV light at the required power, reliability, and stability however presents a formidable task that combines industrial innovations with challenging scientific questions. We will present work on the spectroscopy of tin ions in and out of YAG-laser-driven plasma and present a surprising answer to the key question: what makes that light?