Axion and ALP search with the Any Light Particle Search II experiment at DESY

The Any Light Particle Search II (ALPS II) is a Light-Shining-Through-a-Wall experiment at DESY in Hamburg, Germany, which hunts for axions and axion-like particles in the sub-meV mass range with an axion-photon-photon coupling gα γ γ > 2 × 10⁻¹¹\ GeV⁻¹, improving the sensitivity by a factor of 10³ compared to its predecessors. For this purpose, a high-power laser is directed through a long string of superconducting dipole magnets and a mode-matched optical cavity, where some photons can convert into a beam of axion-like particles. The latter passes through a light-tight barrier, another strong magnetic field and mode-matched optical cavity, where some of the axion-like particles can convert back into photons and be detected. In May 2023, the ALPS II experiment started the initial phase of data taking, in which it employs a heterodyne detection method (HET). Upgrades that will allow ALPS II to reach its full design sensitivity are planned for 2024. In this paper, the status of the initial data taking with ALPS II and the experience gained are described.