Spatial dynamics, thermalization, and gain clamping in a photon condensate

TL;DR

This paper theoretically investigates how pump-spot size and position influence photon condensates, revealing the roles of spatial equilibration, gain clamping, and thermalization, and explaining recent experimental observations.

Contribution

It provides a theoretical framework linking spatial inhomogeneities to gain clamping and thermalization, and suggests ways to engineer condensate structures.

Findings

Thermalization breakdown causes imperfect gain clamping.

Spatial hole burning leads to multimode condensation.

Pump-spot manipulation can control condensate structure.

Abstract

We study theoretically the effects of pump-spot size and location on photon condensates. By exploring the inhomogeneous molecular excitation fraction, we make clear the relation between spatial equilibration, gain clamping and thermalization in a photon condensate. This provides a simple understanding of several recent experimental results. We find that as thermalization breaks down, gain clamping is imperfect, leading to "transverse spatial hole burning" and multimode condensation. This opens the possibility of engineering the gain profile to control the condensate structure.