  The thermodynamical properties of the photon-plasma system had been studied
using statistical physics approach. Photons develop an effective mass in the
medium thus -- as a result of the finite chemical potential -- a photon
Bose-Einstein condensation can be achieved by adjusting one of the relevant
parameters (temperature, photon density and plasma density) to criticality. Due
to the presence of the plasma, Planck's law of blackbody radiation is also
modified with the appearance of a gap below the plasma frequency where a
condensation peak of coherent radiation arises for the critical system. This is
in accordance with recent optical microcavity experiments which are aiming to
develop such photon condensate based coherent light sources. The present study
is also expected to have applications in other fields of physics such as
astronomy and plasma physics.
