The heterodyne sensing system for the ALPS II search for sub-eV weakly interacting particles

Abstract

ALPS II, the Any Light Particle Search, is a second-generation Light Shining through a Wall experiment that hunts for axion-like particles. The experiment is currently transitioning from the design and construction phase to the commissioning phase, with science runs expected to start in 2021. ALPS II plans to use two different sensing schemes to confirm the potential detection of axion-like particles or to verify an upper limit on their coupling strength to two photons of gaγγ ≤ 2 × 10 −11 GeV −1 . This paper discusses a heterodyne sensing scheme (HET) which will be the first scheme deployed to detect the regenerated light. It presents critical details of the optical layout, the length and alignment sensing scheme, design features to minimize spurious signals from stray light, as well as several control and veto channels specific to HET which are needed to commission and operate the instrument and to calibrate the detector sensitivity.

Millimeter‐Wave WISP Search with Coherent Light‐Shining‐Through‐a‐Wall Toward the STAX Project

“…In LSW experiments, the advantage of the coherent wave detection was recognized rather recently in the infrared laser experiment (Any Light Particle Search II; ALPSII). [ 12–14 ] In this work, we show the feasibility of the coherent detection technique for the search of dark photons in the millimeter‐wave range. Although a similar concept was verified at 1–3 GHz, [ 15–17 ] an experiment at 30 GHz is novel.…”

Light-Shining-Through-Walls Experiments

“…The phase of the interference beat note can then be monitored by a photodetector PD M . This system must also be capable of sensing the optical path-length changes between the flat cavity mirrors on the COB [16], although the components that perform this function are not shown in the figure . The technical challenges become even more significant when considering that all of this must be accomplished without compromising the light-tightness of the experiment.…”

A First Application of Machine and Deep Learning for Background Rejection in the ALPS II TES Detector

“…Once commissioned, ALPS II will reach unprecedented sensitivity for an LSW‐type experiment by employing a high‐power infrared laser at a wavelength of 1064 nm, optical cavities for additional power build‐up before and behind the wall, and sensitive photon detectors measuring rates down to $$\approx 10^{-6}$$,Hz. [ 11,12 ] Within a 20 day measurement we aim to probe photon‐ALP couplings down to $$g_{a\gamma } \gtrsim 2\times 10^{-11}\,\mathrm{GeV}^{-1}$$ for masses $$m_\text{a} \lesssim 10^{-4}$$ eV. This would make it possible to probe ALP dark matter scenarios [ 13 ] and axion models that predict a large coupling to photons.…”