Hawking radiation from “phase horizons” in laser filaments?

Belgiorno et al. have reported on experiments aiming at the detection of (the analogue of) Hawking radiation using laser filaments F. Belgiorno et al., Phys. Rev. Lett. 105, 203901 (2010). They sent intense focused Bessel pulses into a nonlinear dielectric medium in order to change its refractive index via the Kerr effect and saw creation of photons orthogonal to the direction of travel of the pulses. Since the refractive index change in the pulse generated a ``phase horizon'' (where the phase velocity of these photons equals the pulse speed), they concluded that they observed the analogue of Hawking radiation. We study this scenario in a model with a phase horizon and a phase velocity very similar to that of their experiment and find that the effective metric does not quite correspond to a black hole. The photons created in this model are not due to the analogue of black hole evaporation but have more similarities to cosmological particle creation. Nevertheless, even this effect cannot explain the observations---unless the pulse has significant small scale structure in both the longitudinal and transverse dimensions.