analogue gravity

Shalva Amiranashvili
Shalva Amiranashvili

Controlling light by light

Shalva Amiranashvili
shalva.amiranashvili@wias-berlin.de
Weierstrass Institute, Mohrenstr. 39, 10117 Berlin, Germany
We discuss propagation of ultrashort solitary pulses in nonlinear single-mode optical fibers. Each pulse creates a moving perturbation of the refractive index; the perturbation is capable to scatter co-propagating pulses. An ultrashort optical soliton serves, under suitable conditions, as an impenetrable mirror for the group-velocity matched small-amplitude waves. Reflection of such waves by a quickly moving mirror in dispersive media is a rich source of the intriguing phenomena including analogue event horizons and radiation at negative frequencies. On the other hand, energy exchange between the scattered pump waves and the soliton provides an effective way to manipulate the soliton, e.g., to fix its frequency or to compress it to a large extent.
Daniele Faccio
Daniele Faccio

Analogue gravity in rotating spacetimes

Daniele Faccio
daniele.faccio@glasgow.ac.uk
University of Glasgow

Superradiant gain is the process in which waves are amplified via their interaction with a rotating body, examples including evaporation of a spinning black hole and electromagnetic emission from a rotating metal sphere. We will first discuss the case of photon fluids, i.e. room temperature superfluids generated by a laser beam propagating in a nonlinear defocusing material. Prior work has already demonstrated the superfluid nature of the 2D beam profile in this setting and we have recently studied that by injecting a vortex pump beam, it is possible to generate a rotating spacetime metric and experimentally identify the horizon and ergosphere. Numerical studies based on the Nonlinear Schrodinger equation now illustrate the conditions under which experiments are expected to observe superradiance by analyzing the optical currents in the system. Finally, we will examine a different scenario, more akin to the sutation examined in 1971 by Zel’dovich, i.e. a rotating cylinder. We elucidate theoretically how superradiance may be realized in the field of acoustics, and predict the possibility of non-reciprocally amplifying or absorbing acoustic beams carrying orbital angular momentum by propagating them through an absorbing medium that is rotating. We discuss a possible geometry for realizing the superradiant amplification process using existing technology.