Ellipticity induced in vacuum birefringence

Understand

We consider signals of photon-photon scattering in laser-based, low energy experiments.

• In particular, we consider the ellipticity induced on a probe beam by a strong background field, and compare it with a recent worldline expression for the photon polarisation flip amplitude.
• When the probe and the background are plane waves, the ellipticity is equal to the flip amplitude.
• Here we investigate the ellipticity-amplitude relation for more physical fields.