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.
@article{arxiv.2304.06374,
title = {Long-lasting XUV activation of helium nanodroplets for avalanche ionization},
author = {C. Medina and A. Ø. Lægdsmand and L. Ben Ltaief and Z. Hoque and A. H. Roos and M. Jurkovič and O. Hort and O. Finke and M. Albrecht and J. Nejdl and F. Stienkemeier and J. Andreasson and E. Klimešová and M. Krikunova and A. Heidenreich and M. Mudrich},
journal= {arXiv preprint arXiv:2304.06374},
year = {2023}
}