Shining Light into the Hidden Sector with ALPS II

The strong CP problem, the existence of dark matter, the transparency of interstellar space to highly energetic photons, anomalies in stellar cooling rates, all of these phenomena suggest that our current understanding of the universe is incomplete.  Axions and axion-like particles residing somewhere in the hidden sector could provide a singular solution to this puzzle. The Any Light Particle Search II (ALPS II) is an experiment based at DESY in Hamburg, Germany, that will hunt for low mass (< 0.1 meV) axion-like particles by taking advantage of their coupling to photons in the presence of a magnetic field. ALPS II will use the light-shining-through-a-wall (LSW) technique, in which a high-power laser is directed through a magnetic field to generate a beam of relativistic axion-like particles that then pass through a wall. Beyond the wall will be another region of magnetic field, where some of the particles will reconvert back to photons. By counting the individual photons after the wall, ALPS II will perform a model-independent measurement of the coupling strength between photons and axion-like particles. In this talk, I will provide a brief introduction to axions and explain where LSW experiments fit into the broader search for these types particles. An overview and status report of ALPS II will also be given, along with a discussion of the optical system, which includes two 122 m long resonators, and the techniques used to detect single photons.