  The energy dependence of the cross sections for electromagnetic diffractive
processes can be well described by a single power, $W^\delta$. For $J/\psi$
photoproduction this holds in the range from 20 GeV to 2 TeV. This feature is
most easily explained by a single pole in the angular momentum plane which
depends on the scale of the process, at least in a certain range of values of
the momentum transfer. It is shown that this assumption allows a unified
description of all electromagnetic elastic diffractive processes. We also
discuss an alternative model with an energy dependent dipole cross section,
which is compatible with the data up to 2 TeV and which shows an energy
behaviour typical for a cut in the angular momentum plane.
