  We investigate the absorption and emission of a 25 nm ZnSe layer, which was
grown on a GaAs buffer and cladded by ZnSSe layers. Due to the coupling of
light with the exciton resonances, polariton modes propagate through the ZnSe
layer. Their interferences appear as additional peaks in the reflection spectra
and can be explained by the effect of spatial dispersion. We present additional
experimental results for the emission of the sample after excitation by a pump
pulse, showing corresponding interference peaks of the polariton modes, whose
maxima strongly decrease to higher energies. Our exact theoretical analysis
shows that the ratio of emission and absorption is given by the population of
the globally defined states of the electromagnetic field, i.e. the polariton
distribution which is generated by the pump pulse. This distribution, being far
from thermal quasiequilibrium, shows pronounced peaks at the polariton modes
depending on the energy of the pump pulse.
