  The focusing of the vacuum modes of a quantized field by a parabolic mirror
is investigated. We use a geometric optics approximation to calculate the
energy density and mean squared field averages for scalar and electromagnetic
fields near the focus. We find that these quantities grow as an inverse power
of the distance to the focus. There is an attractive Casimir-Polder force on an
atom which will draw it into the focus. Some estimates of the magnitude of the
effects of this focusing indicate that it may be observable.
