  We address the question of radiation emission from both perfect and
dispersive mirrors following prescribed relativistic trajectories. The
trajectories considered are asymptotically inertial: the mirror starts from
rest and eventually reverts to motion at uniform velocity. This enables us to
provide a description in terms of in and out states. We calculate exactly the
Bogolubov alpha and beta coefficients for a specific form of the trajectory,
and stress the analytic properties of the amplitudes and the constraints
imposed by unitarity. A formalism for the description of emission of radiation
from a dispersive mirror is presented.
