An intense pulse of light will excite a polarisation wave in nonlinear medium, i.e. a pulsed change in th refractive index that travels locked to the light pulse. This refrctive index chnge is theerfore travelling at the speed of light in the medium - it may be described as an effective medium flowing at the speed of light and it has the same spacetime metric of a black hole. Other, more complicated beams or pulses of light, will likewise exciting a moving refractive index with spedicif features that depend on the specific shape of the light pulse. It is possible to therefore to create not only flowing media bur also, for example, rotating media, oscillating media or accelerating media. These models may be used to study how quantum field theories in these curved spacetimes and study various effects such as black hole evaporation, the dynamical Casimir effect and acceleration radiation. Investigating light in moving media we recently (re)discovered the important role of negative frequencies and more in general, of the negative frequency content of optical waves (see references below for details) in nonlinear optics. REFERENCES: Spatially structured photons that travel in free space slower than the speed of light, D. Giovannini, J. Romero, V. Potocek, G. Ferenczi, F. Speirits, S. M. Barnett, D. Faccio, M. J. Padgett, Science 347, 857 (2015) Negative-frequency dispersive wave generation in quadratic media, M. Conforti, N. Westerberg, F. Baronio, S. Trillo, D. Faccio, Phys. Rev. A, 88, 013829 (2013) Interaction between optical fields and
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