Comparison of Electron and Ion Emission from Xenon Cluster-Induced Ignition of Helium Nanodroplets

The charging dynamics
of helium droplets driven by embedded xenon
cluster ignition in strong laser fields is studied by comparing the
abundances of helium and highly charged Xe ions to the electron signal.
Femtosecond pump–probe experiments show that near the optimal
delay for highly charged xenon the electron yield increases, especially
at low energies. The electron signature can be traced back to the
ionization of the helium environment by Xe seed electrons. Accompanying
molecular dynamics simulations suggest a two-step ionization scenario
in the Xe–He core–shell system. In contrast to xenon,
the experimental signal of the helium ions, as well as low-energy
electron emission show a deviating delay dependence, indicating differences
in the temporal and spacial development of the charge state distribution
of Xe core and He surrounding. From the pump–probe dependence
of the electron emission, effective temperatures can be extracted,
indicating the nanoplasma decay.