Photons were the first bosons to be considered under the quantum statistics known today as the Bose-Einstein statistics. However, they were one of the last quantum gases to undergo Bose-Einstein condensation in a controlled environment, achieved recently in a microcavity filled with a rhodamine solution [1]. On one hand, since these pioneering observations, the principle of light thermalization and condensation in optical cavities has been anticipated to be a much more common phenomenon. On the other hand, the Bose-Einstein condensation contrasts with the common understanding of laser operation being an entirely nonequilibrium phenomenon.

In this talk, I will present our recent results on the Bose-Einstein condensation of photons in a semiconductor device, the vertical-cavity surface-emitting laser (VCSEL) [2]. Firstly, I will introduce the physics behind light thermalization and condensation in semiconductor laser cavities [3]. Next, I will present our measurements of a typical Bose-Einstein condensation behavior when crossing the critical phase-space density and observation a thermalized distribution of photons in the condensate. The observed spectroscopic and caloric properties show all predicted effects for a Bose-Einstein condensate phase transition in thermal equilibrium. Our results offer a new and fresh view of the working principles of semiconductor lasers and have a great potential for technological development for future laser devices [4].

References:

[1] J. Klaers et al., Nature 468, 545-548 (2010)
[2] M. Pieczarka et al., Nature Photonics 18, 1090-1096 (2024)
[3] A. Loirette-Pelous, & J.-J. Greffet, Laser Photonics Rev., 17, 2300366. (2023)
[4] A. Fainstein & G. Usaj, Nature Photonics 18, 999-1001 (2024)