On the observation of vacuum birefringence

Abstract

We suggest an experiment to observe vacuum birefringence induced by intense laser fields. A high-intensity laser pulse is focused to ultra-relativistic intensity and polarizes the vacuum which then acts like a birefringent medium. The latter is probed by a linearly polarized x-ray pulse. We calculate the resulting ellipticity signal within strong-field QED assuming Gaussian beams. The laser technology required for detecting the signal will be available within the next three years. The interactions of light and matter are described by quantum electrodynamics (QED), at present the bestestablished theory in physics. The QED Lagrangian couples photons to charged Dirac particles in a gauge invariant way. At photon energies small compared to the electron mass, ω ≪ m e , electrons (and positrons) will generically not be produced as real particles. Nevertheless, as already stated by Heisenberg and Euler, "...even in situations where the [photon] energy is not sufficient for matter production, its virtual possibility will result in a 'polarization of the vacuum' and hence in an alteration of Maxwell's equations" [1]. These authors were the first to explicitly derive the nonlinear terms induced by QED for small photon energies but arbitrary intensities (see also [2]).The most spectacular process resulting from these modifications presumably is pair production in a constant electric field. This is an absorptive process as photons disappear by disintegration into matter pairs. It can occur for field strengths larger than the critical one given by [3,4] In this electric field an electron gains an energy m e upon travelling a distance equal to its Compton wavelength, λ e = 1/m e . The associated intensity is I c = E 2 c ≃ 4.4 × 10 29 W/cm 2 such that both field strength and intensity * Electronic address: theinzl@plymouth.ac.uk

A Lorentz and gauge invariant measure of laser intensity

“…Taking p as the momentum of a probe photon a 0 also determines the amount of vacuum birefringence in ultrastrong laser fields due to an induced effective metric, h µν = g µν − κ T µν with κ = κ(a 0 ) [16].…”

Photon splitting in a laser field

“…Other processes related to photon-photon scattering and initiated by vacuum polarization in the presence of the superposition of two laser fields, or a laser field and a Coulomb field have been considered in [20,21,22,23].…”

Photon polarization tensor in pulsed Hermite- and Laguerre-Gaussian beams

“…Furthermore, it is certainly interesting to study vacuum birefringence and photon diffraction effects in high-intensity laser beams prepared in a distinct higher Laguerre-or Hermite-Gaussian mode. So far, theoretical studies of these effects typically assumed the high-intensity laser beams to be prepared in the fundamental Gaussian mode [47][48][49][50][51][52][53][54][55]; for an exception cf. Ref.…”