Classical Rayleigh-Jeans Condensation of Light Waves: Observation and Thermodynamic Characterization
Baudin
K
author
Fusaro
A
author
Krupa
K
author
Garnier
J
author
Rica
S
author
Millot
G
author
Picozzi
A
author
2020
Theoretical studies on wave turbulence predict that a purely classical system of random waves can exhibit a process of condensation, which originates in the singularity of the Rayleigh-Jeans equilibrium distribution. We report the experimental observation of the transition to condensation of classical optical waves propagating in a multimode fiber, i.e., in a conservative Hamiltonian system without thermal heat bath. In contrast to conventional self-organization processes featured by the nonequilibrium formation of nonlinear coherent structures (solitons, vortices, ...), here the self-organization originates in the equilibrium Rayleigh-Jeans statistics of classical waves. The experimental results show that the chemical potential reaches the lowest energy level at the transition to condensation, which leads to the macroscopic population of the fundamental mode of the optical fiber. The near-field and far-field measurements of the condensate fraction across the transition to condensation are in quantitative agreement with the Rayleigh-Jeans theory. The thermodynamics of classical wave condensation reveals that the heat capacity takes a constant value in the condensed state and tends to vanish above the transition in the normal state. Our experiments provide the first demonstration of a coherent phenomenon of self-organization that is exclusively driven by optical thermalization toward the Rayleigh-Jeans equilibrium.
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text
10.1103/PhysRevLett.125.244101
Baudin_etal2020
Physical Review Letters
Phys. Rev. Lett.
2020
continuing
periodical
academic journal
125
24
244101
0031-9007