Title: Long-lasting XUV activation of helium nanodroplets for avalanche ionization

Authors: C Medina, A Ø Lægdsmand, L Ben Ltaief, Z Hoque, A H Roos, L Jurkovicová, O Hort, O Finke, M Albrecht, J Nejdl, F Stienkemeier, J Andreasson3, E Klimesová3, M Krikunova, A Heidenreich and M Mudrich

DOI: 10.1088/1367-2630/acd5f6 Date: 05/30/2023

Working Group: WG4

Grant Period: GP1

Grant Period Goal (number): 4.2.2 Energy transfer and collective effects with the potential of enhancing conversion efficiency.

Covered deliverables from the MoU (number): 4.2.2 Energy transfer and collective effects with the potential of enhancing conversion efficiency.

Countries involved: Denmark, Germany, Czech Republic, Spain

Number of female/young/ITC coauthors: 7

Abstract: We study the dynamics of avalanche ionization of pure helium nanodroplets activated by a weak
extreme-ultraviolet (XUV) pulse and driven by an intense near-infrared (NIR) pulse. In addition
to a transient enhancement of ignition of a nanoplasma at short delay times ∼200 fs, long-term
activation of the nanodroplets lasting up to a few nanoseconds is observed. Molecular dynamics
simulations suggest that the short-term activation is caused by the injection of seed electrons into
the droplets by XUV photoemission. Long-term activation appears due to electrons remaining
loosely bound to photoions which form stable ‘snowball’ structures in the droplets. Thus, we show
that XUV irradiation can induce long-lasting changes of the strong-field optical properties of
nanoparticles, potentially opening new routes to controlling avalanche-ionization phenomena in
nanostructures and condensed-phase systems.