# Statistical theory of photon gas in plasma

## TL;DR

This paper explores the thermodynamics of photon gases in plasma, showing how photons acquire effective mass, leading to Bose-Einstein condensation and modified blackbody radiation, with implications for experiments and astrophysics.

## Contribution

It provides a statistical physics framework for photon condensation in plasma, highlighting the effects of plasma on blackbody radiation and photon effective mass, and connects theory with recent experiments.

## Key findings

- Photon effective mass in plasma enables Bose-Einstein condensation.
- Modified Planck's law with a gap below plasma frequency.
- Photon condensate observed in optical microcavity experiments.

## Abstract

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.