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Real-time optical-streak of laser-accelerated ion induced electron solvation in liquid water

by Alexander Prasselsperger

Europe/Berlin
Description

Since the 2000s ion-acceleration by high-power laser systems has boosted a global interest in the physics of this compact source of energetic particles with exceptional properties. The bunches inherently contain large numbers of particles bunched in durations of only a few picoseconds when applied in immediate distance to the source. Moreover, the possibility to pick a probe pulse from the acceleration-driving-laser predestines to study fundamental ion-matter-interactions with temporal resolution that has so far, for protons and ions, not been accessible. As proposed by Gauduel et al. [1] the energy dissipation time within ion tracks can be expected to be higher compared to electron and EM-radiation tracks due to the very high energy deposition in small localised volumes, especially in the Bragg-peak. With an optical streaking setup we were able to confirm this delayed thermalisation experimentally for the first time by imprinting the temporal evolution of the ion-matter-interaction into the spectrum of a chirped probe pulse via solvated electron absorption [2]. Solvation here describes a localised state where a previously ionised electron binds to broken hydrogen-bonds which is

absorbing exactly in the wavelength region of our lasers around 800 nm. Our measurements revealed a >20 ps delay in electron solvation when compared to common models assuming a lower local energy density. This indicates that so far neglected forces might affect electron dynamics. Investigating this currently unexplored parameter range, with high peak current ion bunches in sub-nanosecond durations, represents a great opportunity for improving our understanding of the thermalisation process within ion tracks on ultra-short timescales, with potential implications, e.g., for ionoacoustics, determination of the ions' radiobiological effectiveness (RBE) or the flash-effect in radiobiology, to name just a few applications [3].

 

[1] Y. A. Gauduel et al. Eur. Phys. J. D 60 (2010) 121

[2] A. Prasselsperger et al. Phys. Rev. Lett. 127 (2021) 186001

[3] P. R. Bolton et al. CRC Press, Taylor & Francis Group ed1 (2018) ISBN 1498766412