  We study theoretically the dynamical Casimir effect in an exciton-polariton
condensate that is suddenly created by an ultrashort laser pulse at normal
incidence. As a consequence of the abrupt change of the quantum vacuum,
Bogoliubov excitations are generated. The subsequent evolution, governed by
polariton interactions and losses, is studied within a linearized truncted
Wigner approximation. We focus in particular on the momentum distribution and
spatial coherence. The limiting behavior at large and small momenta is
determined analytically. A simple scaling relation for the final condensate
depletion as a function of the system parameters is found and the correlation
length is shown to depend linearly on the condensate depletion.
