Penrose Superradiance in Nonlinear Optics.

Particles or waves scattered from a rotating black hole can be amplified through the process of Penrose superradiance, although this cannot currently be observed in an astrophysical setting. Here we theoretically show that analog Penrose superradiance arises naturally in the field of nonlinear optics. A loosely focused signal beam can experience gain or amplification as it glances off a strong vortex pump beam in a nonlinear defocusing medium. Amplification occurs only with the generation and trapping of negative norm modes in the core of the pump vortex, as predicted by Penrose. Our results elucidate a new regime of nonlinear optics involving the notion of an ergoregion, providing further insight into the processes and transient dynamics involved in Penrose superradiance.