Rotating Acoustic Black Holes and Superradiance in a Nonlinear Optical Cavity

The analogy between sound waves propagation in inhomogeneous fluids and light propagation in curved spacetime [1] could enable laboratory tests of relevant phenomena in black hole physics. So far, experimental proposals have been based on superfluid He and Bose-Einstein condensates (BECs) [2]. Recently however, it has been shown that, exploiting the relation between nonlinear optics and fluid dynamics, acoustic black holes can be created also in self-defocusing optical cavities. An optical field in self-defocusing media can be described in terms of a (2+1) "photon-fluid" on which linear perturbations, i.e. sound waves, experience an effective curved spacetime depending on the background flow (i.e. on the optical field profile). Since in an optical cavity the background flow is "pinned" by the driving field, the injection of a suitable optical vortex beam allows the generation of acoustic ergoregions and event horizons [3]. These results suggest the possibility to observe acoustic superradiance [4] from optical vortices in self-defocusing cavities