  Doping a helium nanodroplet with a tiny xenon cluster of a few atoms only,
sparks complete ionization of the droplet at laser intensities below the
ionization threshold of helium atoms. As a result, the intrinsically inert and
transparent droplet turns into a fast and strong absorber of infrared light.
Microscopic calculations reveal a two-step mechanism to be responsible for the
dramatic change: Avalanche-like ionization of the helium atoms on a femtosecond
time scale, driven by field ionization due to the quickly charged xenon core is
followed by resonant absorption enabled by an unusual cigar-shaped nanoplasma
within the droplet.
