Speaker: Gerhard Paulus (Helmholtz Institute Jena, Germany)

Strong electromagnetic fields polarize vacuum such that it becomes birefringent. Not surprisingly, the effect is tiny, even if petawatt-class lasers are used for inducing the effect and X-ray lasers for probing it. Quite obviously, the performance of the required X-ray polarimeters is the decisive bottleneck: an extinction ratio of 10¹¹ or better is required. Gerhard Paulus and his team have been working since more than 10 years to remove the bottleneck. He will report how close they have come to the feasibility of a promising demonstration of vacuum birefringence. He will also explain how to design a reasonable experiment and which mistakes to avoid.