Spatiotemporal Thermalization and Adiabatic Cooling of Guided Light Waves.

We propose and theoretically characterize three-dimensional spatiotemporal thermalization of a continuous-wave classical light beam propagating along a multimode optical waveguide. By combining a nonequilibrium kinetic approach based on the wave turbulence theory and numerical simulations of the field equations, we anticipate that thermalizing scattering events are dramatically accelerated by the combination of strong transverse confinement with the continuous nature of the temporal degrees of freedom. In connection with the blackbody catastrophe, the thermalization of the classical field in the continuous temporal direction provides a novel intrinsic mechanism for adiabatic cooling and spatial beam condensation. This process of adiabatic cooling is distinct from other mechanisms of thermalization and provides new insights into the dynamics of far-from-equilibrium closed systems and their route to thermalization.