Amplified Light Beam Cooling via Emergent Onsager's Irreversible Thermodynamics

TL;DR

This paper introduces a novel method for amplifying light beam brightness and coherence using emergent thermodynamics principles in nonlinear optical systems, surpassing traditional cooling techniques.

Contribution

It presents a new approach leveraging Onsager's irreversible thermodynamics and forbidden chemical potentials to achieve amplified optical beam cooling and increased coherence.

Findings

Optical power increased by 16 times after 800 cooling cycles.

Fundamental mode occupancy reached 90%.

Demonstrated feasibility in multimode optical waveguides.

Abstract

High-brightness coherent light source is at the heart of optical technology and yet challenging to achieve. Here, we propose an unconventional approach that utilizes the "forbidden chemical" in optical thermodynamics to convert any incoming light beam into a high-brightness, high-spatial-coherence light beam in multimode nonlinear optical waveguide systems, in contrast to evaporative cooling in cold atoms where the brightness is instead reduced. This approach is powered by the fact that light in nonlinear multimode structures undergoes an irreversible thermalization process triggered by its own photon-photon interactions. Moreover, the key characteristics in statistical mechanics, the optical temperature and chemical potential can be widely tuned in photonic systems. As such, when the chemical potential of an optical reservoir is designed to locate at the forbidden band of the probe bosonic system, it can never reach thermal equilibrium with the probe hence endlessly pumping the probe system towards an enhanced brightness and spatial coherence. This amplified cooling of light beam is revealed via both Onsager's irreversible thermodynamics theory and numerical simulations. Akin to this effect, the inverse photonic transport currents emerge due to the negative off-diagonal Onsager coefficients. We demonstrate the feasibility of the amplified beam cooling using a coupled multimode optical waveguide system and show that after 800 rounds of amplified cooling, the optical power of an incoming beam is enhanced by 16 times, meanwhile the fundamental mode occupancy is increased to 90%. These findings unveil an anomalous optical phenomenon and a new route toward high-quality light sources.