The ALPS-II experiment, Any Light Particle Search II at DESY in Hamburg, will look for light (m < 10−4 eV) new fundamental bosons (e.g., axion-like particles, hidden photons and other WISPs) in the next years by the means of a light-shining-through the wall setup.
A few years ago, its predecessor had constrained the coupling to photons of axion-like particles (ALPS) to gaγ ≤ 7·10−8 GeV− 1, m ≤ 10−4 eV.
Several improvements are foreseen to reach much better sensitivities (gaγ ≤ 7 · 10 −11 GeV−1). One of the main modifications which have been done is the substitution of the CCD camera by two microcalorimetric W-TESs (Transition Edge Sensors with tungsten chips). These TESs, operated at 80 mK have already allowed single infrared photons detections as well as non-dispersive spectroscopy with very low background rates.
The detection efficiency for such TES is > 95 % and the dark count rate < 10-2 s-1 for 1064 nm photons. At this wavelength, the intrinsic dark count rate is of 10-4 s-1. The relative energy resolution for 1064 nm signals is < 8%. In order to bias accurately the device and for reading purposes, TESs are inductively coupled to a SQUID (Superconducting Quantum Interference Device).
In the near future, complete characterization, calibration and optimization (e.g., background suppression) need to be finalized. The latest progress in this task will be presented as well as next steps planned for future developments.
