Probing vacuum birefringence under a high-intensity laser field with gamma-ray polarimetry at the GeV scale

Probing vacuum structures deformed by high intense fields is of great interest in general. In the context of quantum electrodynamics (QED), the vacuum exposed by a linearly polarized high-intensity laser field is expected to show birefringence. We consider the combination of a 10 PW laser system to pump the vacuum and 1 GeV photons to probe the birefringent effect. The vacuum birefringence can be measured via the polarization flip of the probe $\gamma$-rays which can also be interpreted as phase retardation of probe photons. We provide theoretically how to extract phase retardation of GeV probe photons via pairwise topology of the Bethe-Heitler process in a polarimeter and then evaluate the measurability of the vacuum birefringence via phase retardation given a concrete polarimeter design with a realistic set of laser parameters and achievable pulse statistics.

Figure 1

Conceptual experimental setup to investigate the laser-induced vacuum birefringence effect. (a) Definitions of coordinates with respect to the linear polarization plane of the Compton seed laser field and interaction points are provided. (b) Colliding beam geometry with the alignment of the incident electron beam, the parabola mirrors with pinholes and a polarimeter. $CP$, IP, and DP indicate Compton scattering Point, Interaction Point, and Detection Point, respectively. A distance $l$ between $CP$ and IP and a distance $d$ between $CP$ and DP are introduced. The used electrons are bent in advance of crossing with a pumping laser pulse at IP.

Figure 2

(a) Incident $\gamma$-ray yields as a function of the emission angle for orthogonal linear polarization states, respectively. (b) The degree of linear polarization of $\gamma$-rays. The polarization-flip effect due to the laser-induced birefringence depends on the emission angle. (c) The corresponding phase retardation $G$.

Figure 3

Configuration of the detection elements for $\gamma$-ray polarimetry and spectroscopy via the Bethe-Heitler process on a thin converter located at the origin.

Figure 4

The angular distributions of $e^{-}{e}^{+}$ emission planes with respect the reference plane (${\varphi }_0=0$). The open blue and closed red points depict the angular distributions for $G=0$ and 0.72, respectively, with fitting results based on Eq. (30). The total number of $e^{-}{e}^{+}$ pairs was assumed to be $10^4$ with a single pair production per shot in this simulation. The vertical error bars show statistical errors in the simulation.