Observation of Joule-Thomson photon-gas expansion

TL;DR

This paper demonstrates an all-optical Joule-Thomson expansion where photon-photon interactions cause the optical gas to cool abruptly to zero temperature, enabling efficient channeling into the fundamental mode.

Contribution

It introduces a novel all-optical Joule-Thomson expansion process mediated by photon interactions, with experimental validation in nonlinear waveguide systems.

Findings

Optical gas temperature drops abruptly to zero during expansion.

Light can be efficiently channeled into the fundamental mode.

Post-expansion state stability is ensured through irreversible energy conversion.

Abstract

In recent years, a self-consistent optical thermodynamic framework has emerged that offers a systematic methodology to understand, harness and exploit the complex collective dynamics of multimode nonlinear systems. These developments now allow consideration of a series of longstanding problems in optics, including the prospect of funnelling the entire power flowing in a multimode system into its ground state, for which no methodology currently exists. Here, we demonstrate an all-optical Joule-Thomson expansion process mediated by photon-photon interactions whereby the temperature of the optical gas drops abruptly to zero. Our experiments in various configurations of coupled multicore nonlinear waveguide arrangements illustrate how light undergoing expansion-induced cooling can be channelled from arbitrary input states into the fundamental mode with near-unity efficiency. We show that the stability of the post-expansion state is ensured through an irreversible process of energy conversion. The all-optical thermodynamic phenomena explored in this study may enable innovative techniques where various uncorrelated but identical sources are merged into a unified spatially coherent state, offering a route for direct beam combining.