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If the intensity of a light pulse is high enough, photons in the pulse can interact and behave like molecules in a fluid. Fluid-like phenomena such as rogue waves, superfluidity, and turbulence have all been observed in light pulses. Now, a team of scientists from the University of Lille, France, and the University of Ferrara, Italy, has induced photon behavior reminiscent of that seen in water flow following the collapse of a dam. According to the researchers, their experimental setup could be used to explore optical counterparts of other fluid phenomena that involve fast changes in the photon flow of propagating light pulses, such as the shock generated when a moving piston compresses a gas.

When a dam breaks, water can suddenly flow much faster over the dam. Shock waves initially propagate through the water’s surface, followed by a regime where the height of the water flowing over the ruptured dam increases smoothly to some maximum.

To mimic this scenario with light pulses, Xu and colleagues sent light from a continuous-wave laser down an optical fiber. They abruptly increased the laser power—replicating the moment a dam breaks—and then monitored how the light pulse evolved. As for a dam, features analogous to shock waves initially propagated down the fiber, followed by a slow ramp in power until the maximum power of light was reached. When the team increased the magnitude of the power jump above a threshold value, they observed a regime, unseen in a dam break. In this “cavitation” regime, the trough of the shock wave becomes completely empty—the propagating beam temporarily goes dark.


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