LAUSR

The Any Light Particle Search II (ALPS II) is an experiment currently being built at DESY in Hamburg, Germany, that will use a light-shining-through-a-wall (LSW) approach to search for axion-like particles. ALPS II represents a significant step forward for these types of experiments as it will use 24 superconducting dipole magnets, along with dual high-finesse, 122 m long optical cavities. This paper gives the first comprehensive recipe for the realization of the idea, proposed over 30 years ago, to use optical cavities before and after the wall to increase the power of the regenerated photon signal. This concept will allow the experiment to achieve a sensitivity to the coupling between axion-like particles and photons down to g = 2e-11 1/GeV for masses below 0.1 meV, more than three orders of magnitude beyond the sensitivity of previous laboratory experiments. The layout and main components that define ALPS II are discussed along with plans for reaching design sensitivity. A set of top level requirements for the subsystems is also provided for the first time and includes the requirements on the coherence and spatial mode matching of the cavity eigenmodes. An accompanying paper (Hallal, et al [1]) offers a more in-depth description of the heterodyne detection scheme, the first of two independent detection systems that will be implemented in ALPS II.