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arXiv · 2012.02235

Energy and wave-action flows underlying Rayleigh-Jeans thermalization of optical waves propagating in a multimode fiber

K. Baudin·A. Fusaro·J. Garnier·N. Berti·K. Krupa·I. Carusotto·S. Rica·G. Millot·A. Picozzi
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Abstract

The wave turbulence theory predicts that a conservative system of nonlinear waves can exhibit a process of condensation, which originates in the singularity of the Rayleigh-Jeans equilibrium distribution of classical waves. Considering light propagation in a multimode fiber, we show that light condensation is driven by an energy flow toward the higher-order modes, and a bi-directional redistribution of the wave-action (or power) to the fundamental mode and to higher-order modes. The analysis of the near-field intensity distribution provides experimental evidence of this mechanism. The kinetic equation also shows that the wave-action and energy flows can be inverted through a thermalization toward a negative temperature equilibrium state, in which the high-order modes are more populated than low-order modes. In addition, a Bogoliubov stability analysis reveals that the condensate state is stable.

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K. Baudin, A. Fusaro, J. Garnier, N. Berti, K. Krupa, I. Carusotto, S. Rica, G. Millot, A. Picozzi. 2020-12-03. Energy and wave-action flows underlying Rayleigh-Jeans thermalization of optical waves propagating in a multimode fiber. https://doi.org/10.1209/0295-5075/134/14001

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