The meta-stable and stable thermal equilibrium of a photonic mesh lattice

Abstract: n the limit of short optical pulses, an optical double loop experiment can be modelled using a photonic mesh lattice describing a system of coupled wave fields in discrete space and time. For an alternating phase modulation, the photonic mesh lattice possesses a linear dispersion relation with two bands that are completely isolated. Here we study the process of thermalisation of a single band, using the framework of weak wave turbulence. Previous experimental and numerical observations suggest that for single band excitation, a Rayleigh-Jeans distribution is observed among the normal modes, seeming to reach a thermal equilibrium [1]. However, for longer time scales, a power leakage process occurs destabilising the single band Rayleigh-Jeans. Eventually the power is equally split between bands, reaching a full thermal equilibrium in both bands simultaneously, with the total linear energy tending to zero. As a consequence of this, the temperature and chemical potential are now dependent on one another and cannot be arbitrarily chosen.

[1] A. L. Marques Muniz and F. O. Wu and P. S. Jung and M. Khajavikhan and D. N. Christodoulides and U. Peschel : Observation of photon-photon thermodynamic processes under negative optical temperature conditions Science 379 n.6636, 1019-1023 (2023)

Mathematicsfluid dynamics

Audience: researchers in the topic

Fluids and Structures Seminar @ UEA