  Real and momentum space spectrally resolved images of microcavity polariton
emission in the regime of condensation are investigated under non resonant
excitation using a laser source with reduced intensity fluctuations on the
timescale of the exciton lifetime. We observe that the polariton emission
consists of many macroscopically occupied modes. Lower energy modes are
strongly localized by the photonic potential disorder on a scale of few
microns. Higher energy modes have finite k-vectors and are delocalized over
10-15 microns. All the modes exhibit long range spatial coherence comparable to
their size. We provide a theoretical model describing the behavior of the
system with the results of the simulations in good agreement with the
experimental observations. We show that the multimode emission of the polariton
condensate is a result of its nonequilibrium character, the interaction with
the local photonic potential and the reduced intensity fluctuations of the
excitation laser.
