Phase transitions of photon fluid flows driven by a virtual all-optical piston

TL;DR

This study explores phase transitions in a photon fluid driven by an all-optical piston, revealing shock, rarefaction, and cavitation phenomena, and tests theoretical models of dispersive shock waves in nonlinear optics.

Contribution

It demonstrates experimentally and theoretically the phase transitions and cavitation in photon fluids driven by an optical piston, extending shock wave physics to dispersive optical systems.

Findings

Observation of cross-over from 2-shocks to 2-rarefaction waves.

Detection of cavitating states at critical amplitudes.

Identification of vacuum points marking new regimes in photon fluids.

Abstract

The piston problem, i.e. the dynamics in a uniform gas at rest under the action of a moving piston is fundamental problem of physics and a canonical case study in shock wave physics. We investigate theoretically and experimentally the analogous problem for a photon fluid, which turns out to be strongly influenced by the dispersive character of the problem. The experiment makes use of a fiber optics setup where an all-optically controlled quasi instantaneous change of frequency of the input light mimics the piston action. We show that the flow exhibits phase transitions which involve cross-over from regimes characterized by 2-shocks (pushing piston) to 2-rarefaction waves (retracting piston), with the appearance of cavitating states at critical amplitudes of the jump. Importantly, the appearance of vacuum points into the 2-shock marks the transition to a regime which is unique to the photon fluid. Our observations allow for the extensive and quantitative test of the state of the art description of the dispersive Riemann problem, i.e. Whitham modulation theory, applied to the universal defocusing nonlinear Schr\"odinger equation.