The Any Light Particle Search experiment at DESY

The Any Light Particle Search (ALPS~II) 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 and fulfill the requirements for being dark matter. ALPS~II aims to measure an axion-to-photon coupling of $2\times 10^{-11}\,\mathrm{GeV^{-1}}$, which is several orders of magnitude better than that of previous LSW experiments and will thus investigate a new parameter range. The increased performance is achieved by enhancing the magnetic field interaction length to 2 $\times$ 106\,m and by amplifying the signal in an optical cavity on each side of a light-tight barrier. The expected signal is in the order of 1 photon per day, which will be measured by photon detectors with very low dark count rates of $\mathcal O(10^{-6}\,\mathrm{Hz})$. This article gives a technical overview on the experiment design, previous and ongoing investigations and the current status with focus on the single photon detection.