  We report on the generation of a three-octave-wide supercontinuum extending
from the vacuum ultraviolet (VUV) to the near-infrared, spanning at least 113
to 1000 nm (i.e., 11 to 1.2 eV), in He-filled hollow-core kagome-style photonic
crystal fiber. Numerical simulations confirm that the main mechanism is a novel
and previously undiscovered interaction between dispersive-wave emission and
plasma-induced blueshifted soliton recompression around the fiber zero
dispersion frequency. The VUV part of the supercontinuum, which modeling shows
to be coherent and possess a simple phase structure, has sufficient bandwidth
to support single-cycle pulses of 500 attosecond duration. We also demonstrate,
in the same system, the generation of narrower-band VUV pulses, through
dispersive-wave emission, tunable from 120 to 200 nm with efficiencies
exceeding 1% and VUV pulse energies in excess of 50 nJ.
