Photonic ferromagnetic-like spontaneous mode-locking phase transition with replica symmetry breaking in multimode Nd:YAG laser

TL;DR

This paper demonstrates replica symmetry breaking in the spontaneous mode-locking phase of a conventional multimode Nd:YAG laser, revealing a new phase transition linked to disorder and mode competition, with potential applications in laser threshold identification.

Contribution

It provides the first experimental evidence of RSB in a standard multimode laser, distinct from cavityless random lasers, and proposes RSB as a marker for laser threshold detection.

Findings

RSB observed in spontaneous mode-locking of Nd:YAG laser

High losses suppress RSB, leading to replica-symmetric emission

RSB transition can serve as a threshold indicator in multimode lasers

Abstract

The recent reports of the replica symmetry breaking (RSB) phenomenon in photonic experiments [1-5] boosted the understanding of the role of disorder in multimode lasers, as well as helped to settle enlightening connections [6-13] with the statistical physics of complex systems. RSB manifests when identically-prepared system replicas reach distinct states, yielding different measures of observable quantities [14]. Here we demonstrate the RSB in the spontaneous mode-locking regime of a conventional multimode Nd:YAG laser in a closed cavity. The underlying mechanism is quite distinct from that of the RSB spinglass phase in cavityless random lasers with incoherently-oscillating modes. Here, a specific nonuniform distribution of the gain takes place in each pulse, and frustration is induced since the coherent oscillation of a given subset of longitudinal modes dominates and simultaneously inhibits the others. Nevertheless, when high losses are introduced only the replica-symmetric amplified stimulation emission is observed. We therefore suggest that the RSB transition can be used as an identifier of the threshold in standard multimode lasers, as recently proposed and demonstrated for random lasers [1,2].