Probing the quantum vacuum: Our path to measuring light-by-light scattering at CALA

At sufficient electromagnetic field strength, the classical description of the vacuum is expected to break down. Once the field strength approaches the critical Schwinger limit (E~10^18 V/m, I~10^29 W/cm²), quantum electrodynamics predict particle pairs to be „boiled“ from the vacuum. While intensities achievable with high power lasers today are still orders of magnitude below this limit, the vacuum fluctuations give rise to effects such as vacuum birefringence or light-by-light scattering. Here I will introduce an experiment being set up at the Centre for Advanced Laser Applications (CALA) in Garching near Munich to search for light-by-light scattering with a Petawatt class laser. By colliding two intense laser pulses with O(1e20) photons each, we expect a few (<10) photons to scatter into our detector. I will present the design, theoretical predictions and preliminary measurements on the expected background signals. The results so far indicate we may be able to measure light-by-light scattering in the all-optical regime for the first time in the near future.