Light-Shining-Through-A-Wall: The ALPS II experiment at DESY

The ALPS II at DESY in Hamburg is a light-shining-through-a-wall (LSW) experiment searching for axion-like elementary particles in the sub eV mass range, which are motivated by astrophysics and cosmology. ALPS II aims at an axion-photon coupling sensitivity which is several orders of magnitude better than that of previous LSW experiments and will thus investigate a new parameter range. This is achieved by an increased magnetic field interaction length and by optical cavities on both sides of the wall, which further amplify the signal. In this talk the working principle of LSW experiments and the uniqueness and technological challenges of the ALPS II experiment will be explained. Interim results of previous investigations will be presented as well as the current status. By converting axions to photons, we expect a rate of only 1 photon per day. The two sophisticated detector schemes, coherent heterodyne detection and a cryogenic single photon detector, are also presented and their implementation in the ALPS II experiment is discussed. ALPS II is aiming at a first data run in late 2021