  We demonstrate that the process of evaporative cooling, as associated with
the cooling of atomic gases, can also be employed to condense a system of
photons giving rise to coherent properties of the light. The system we study
consists of photons in a high-quality Fabry-Perot cavity with photon
interactions mediated by a nonlinear atomic medium. We predict a macroscopic
occupation of the lowest energy mode and evaluate the conditions for realizing
a narrow spectral width indicative of a long coherence time for the field.
