Volume 134, Number 1, April 2021
|Number of page(s)||7|
|Section||Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics|
|Published online||17 May 2021|
Energy and wave-action flows underlying Rayleigh-Jeans thermalization of optical waves propagating in a multimode fiber(a)
1 Laboratoire Interdisciplinaire Carnot de Bourgogne, CNRS, Université Bourgogne Franche- Comté - Dijon, France
2 CEA, DAM, DIF - F-91297 Arpajon, France
3 CMAP, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris - 91128 Palaiseau Cedex, France
4 Institute of Physical Chemistry Polish Academy of Sciences - 01-224 Warsaw, Poland
5 INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento - I-38123 Povo (TN), Italy
6 Universidad Adolfo Ibáñez - Peñalolén, 7910000 Santiago, Chile
7 Institut Universitaire de France (IUF) - 1 rue Descartes, 75005 Paris, France
Received: 3 December 2020
Accepted: 23 March 2021
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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