  We study the consequences of dissipation in homogeneous media when the system
is subject to a sudden change, thereby producing pairs of correlated
quasi-particles with opposite momenta. We compute both the modifications of the
spectrum, and those of the correlations. In particular, we compute the final
coherence level, and identify the regimes where the state is non-separable. To
isolate the role of dissipation, we first consider dispersive media and study
the competition between the intensity of the jump which induces some coherence,
and the temperature which reduces it. The contributions of stimulated and
spontaneous emission are clearly identified. We then study how dissipation
modifies this competition.
