F. Belgiorno

Hawking radiation from ultrashort laser pulse filaments

Event horizons of astrophysical black holes and gravitational analogues have been predicted to excite the quantum vacuum and give rise to the emission of quanta, known as Hawking radiation. We experimentally create such a gravitational analogue using ultrashort laser pulse filaments and our measurements demonstrate a spontaneous emission of photons that confirms theoretical predictions.

Negative frequency resonant radiation

Soliton resonant radiation emission is predicted to lead to a second mode that originates from the negative frequency branch of the dispersion relation. Measurements in both bulk media and photonic crystal fibres confirm our predictions.

Analogue gravity phenomenology : analogue spacetimes and horizons, from theory to experiment

Black Holes and Hawking Radiation in Spacetime and its Analogues.- Survey of Analogue Spacetimes.- Cosmological Particle Creation in the Lab.- Irrotational, Two-Dimensional Surface Waves in Fluids.- The Basics of Water Waves Theory for Analogue Gravity.- The Cerenkov Effect Revisited: From Swimming Ducks to Zero Modes in Gravitational Analogues.- Some Aspects of Dispersive Horizons: Lessons from Surface Waves.- Classical Aspects of Hawking Radiation Verified in Analogue Gravity Experiment.- Understanding Hawking Radiation from Models of Atomic Bose-Einstein Condensates.- Transformation Optics.- Laser Pulse Analogues for Gravity.- An All-Optical Event Horizon in an Optical Analogue of a Laval Nozzle.- Lorentz Breaking Effective Field Theory and Observational Tests.- The Topology of Quantum Vacuum.- Einstein^2 :Brownian Motion Meets General Relativity.- Astrophysical Black Holes: Evidence of a Horizon?.

Dielectric black holes induced by a refractive index perturbation and the Hawking effect

We consider a 4D model for photon production induced by a refractive index perturbation in a dielectric medium. We show that, in this model, we can infer the presence of a Hawking type effect. This prediction shows up both in the analogue Hawking framework, which is implemented in the pulse frame and relies on the peculiar properties of the effective geometry in which quantum fields propagate, as well as in the laboratory frame, through standard quantum field theory calculations. Effects of optical dispersion are also taken into account, and are shown to provide a limited energy bandwidth for the emission of Hawking radiation.

Experimental evidence of analogue Hawking radiation from ultrashort laser pulse filaments

Curved space–times and, in particular, event horizons of astrophysical black holes are expected to excite the quantum vacuum and give rise to an emission of quanta known as Hawking radiation. Remarkably, many physical systems may be considered analogous to black holes and as such hold promise for the detection of Hawking radiation. In particular, recent progress in the field of transformation optics, i.e. the description of optical systems in terms of curved space–time geometries, has led to a detailed description of methods for generating, via superluminal dielectrics, a blocking horizon for photons. Our measurements highlight the emission of photons from a moving refractive index perturbation induced by a laser pulse that is in quantitative agreement with the Hawking model. This opens an intriguing and readily accessible observation window into quantum field theory in curved space–time geometries.

Soliton-induced relativistic-scattering and amplification.

Solitons are of fundamental importance in photonics due to applications in optical data transmission and also as a tool for investigating novel phenomena ranging from light generation at new frequencies and wave-trapping to rogue waves. Solitons are also moving scatterers: they generate refractive index perturbations moving at the speed of light. Here we found that such perturbations scatter light in an unusual way: they amplify light by the mixing of positive and negative frequencies, as we describe using a first Born approximation and numerical simulations. The simplest scenario in which these effects may be observed is within the initial stages of optical soliton propagation: a steep shock front develops that may efficiently scatter a second, weaker probe pulse into relatively intense positive and negative frequency modes with amplification at the expense of the soliton. Our results show a novel all-optical amplification scheme that relies on soliton induced scattering.

Quantum Radiation from Superluminal Refractive-Index Perturbations

We analyze in detail photon production induced by a superluminal refractive-index perturbation in realistic experimental operating conditions. The interaction between the refractive-index perturbation and the quantum vacuum fluctuations of the electromagnetic field leads to the production of photon pairs.

The Dirac equation in Kerr-Newman-Ads black hole background

We consider the Dirac equation on the Kerr–Newman–AdS black hole background. We first perform the variable separation for the Dirac equation and define the Hamiltonian operator H. Then we show that for a massive Dirac field with mass μ≥1/(2l), where l is linked to the cosmological constant Λ by Λ≕−3/l2, essential self-adjointness of H on C0∞((r+,∞)×S2)4 is obtained even in presence of the boundarylike behavior of infinity in an asymptotically AdS black hole background. Furthermore, qualitative spectral properties of the Hamiltonian are taken into account and in agreement with the existing results concerning the case of stationary axisymmetric asymptotically flat black holes we infer the absence of time-periodic and normalizable solutions of the Dirac equation around the black hole in the nonextremal case.

Sonoluminescence as a QED vacuum effect: probing Schwinger's proposal

Several years ago Schwinger proposed a physical mechanism for sonoluminescence in terms of photon production due to changes in the properties of the quantum-electrodynamic (QED) vacuum arising from a collapsing dielectric bubble. This mechanism can be re-phrased in terms of the Casimir effect and has recently been the subject of considerable controversy. This paper probes Schwingers suggestion in detail: using the sudden approximation we calculate Bogolubov coefficients relating the QED vacuum in the presence of the expanded bubble to that in the presence of the collapsed bubble. In this way we derive an estimate for the spectrum and total energy emitted. We verify that in the sudden approximation there is an efficient production of photons, and further that the main contribution to this dynamic Casimir effect comes from a volume term, as per Schwingers original calculation. However, we also demonstrate that the timescales required to implement Schwingers original suggestion are not physically relevant to sonoluminescence. Although Schwinger was correct in his assertion that changes in the zero-point energy lead to photon production, nevertheless his original model is not appropriate for sonoluminescence. In other work we have developed a variant of Schwingers model that is compatible with the physically required timescales.

SONOLUMINESCENCE : BOGOLUBOV COEFFICIENTS FOR THE QED VACUUM OF A TIME-DEPENDENT DIELECTRIC BUBBLE

We extend Schwingers ideas regarding sonoluminescence by explicitly calculating the Bogolubov coefficients relating the QED vacuum states associated with changes in a dielectric bubble. Sudden (non-adiabatic) changes in the refractive index lead to an efficient production of real photons with a broadband spectrum, and a high-frequency cutoff that arises from the asymptotic behaviour of the dielectric constant.