Coherence dynamics in microcavities and polariton lasers

We study theoretically the second-order coherence g((2))(0) of light emitted by polariton lasers, i.e., devices based on stimulated relaxation and condensation of exciton-polaritons in microcavities. We solve kinetic equations for the polaritons in different approximations and show that (i) the coherence introduced into the polariton condensate by an external source can be conserved by the system over a macroscopically long time, and (ii) if the total number of polaritons is fixed by the excitation conditions, the correlations between the populations of the ground and excited polariton states can also result in the spontaneous buildup of second-order coherence in the polariton condensate. Both results are obtained neglecting polariton-polariton interactions in the condensate.