  In anticipation of upcoming two-photon double ionization of atoms and
particularly Helium, under strong short wavelength radiation sources (45 eV),
we present quantitative signatures of direct two-photon double ejection, in the
photoelectron spectrum (PES) and the peak power dependence, that can be
employed in the interpretation of related data. We show that the PES provides
the cleanest signature of the process. An inflection (knee) in the laser power
dependence of double ionization is also discernible, within a window of
intensities which depends on the pulse duration and cross sections
