The A2 Collaboration at the Mainz Microtron MAMI measures photon absorption cross sections using circularly and linearly polarized 'Bremsstrahlung' photons up to an energy of ~1.5GeV and a polarized Frozen Spin Target. We use a 4 π detection system with the 'Crystal Ball' as central part. Our Frozen Spin Target provides both longitudinally and transversely polarized protons and deuterons.
In this paper the apparatus will be described. Double polarized experiments for the investigation of the nucleons excitation spectrum via meson production and our Compton program to measure the proton polarizabilities will be briefly discussed.