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.

Figure 1

Experimental layout used for detecting analogue Hawking radiation. The input laser pulse is focused into a sample of fused silica (FS) using an axicon or lens ($F$). An imaging lens ($I$) collects the photons emitted at 90° and sends them to an imaging spectrometer coupled to a cooled CCD camera.

Figure 2

(a) Measured CCD photo-electron ($p\mathrm{\text{−}}e$) counts generated by the fused silica fluorescence spectrum. (b) Prediction of the Hawking emission spectral range for the case of fused silica: $n_0$ (blue solid line) and $n_0+\delta n$ (green dashed line) with $\delta n=0.001$. The shaded area indicates the spectral emission region predicted for a Bessel filament.

Figure 3

(a) Spectra generated by a Bessel filament. Five different curves are shown corresponding to a reference spectrum obtained with a Gaussian pulse (black line) and indicated Bessel energies (in $\mu \mathrm{J}$). Dashed lines are guides for the eye. The solid line connects the spectral peaks, highlighting the $\sim 40\mathrm{nm}$ shift with increasing energy, in close agreement with the predicted 45 nm shift. (b) Bandwidths at FWHM and RIP $\delta n$ versus input energy and intensity. Solid line: linear fit $\delta n=n_{2}I$ with $n_2=2.8\times {10}^{-16}{\mathrm{cm}}^2/\mathrm{W}$.

Figure 4

Spectra generated by the spontaneous filament. (a)–(b) shaded areas: spectra measured for two different positions of the imaging spectrometer input slit. The light gray curves in both figures show the spectrum measured with the input split fully open. The filament, imaged from the side at 90°, is shown in (c) and (d). The vertical white lines show the position of the input slit.