Development of wavelength shifter coated reflectors for the ArDM argon dark matter detector

TL;DR

This paper investigates and optimizes wavelength shifter coated reflectors for the ArDM liquid argon dark matter detector, focusing on light yield enhancement and reflection properties through various coatings and substrates.

Contribution

It presents a comprehensive study of different TPB coating techniques and substrates, providing optimized parameters for the ArDM detector's light collection system.

Findings

TPB coatings significantly improve light reflection in the detector.

Optimized coating thicknesses enhance light yield and reflectivity.

Large coated reflector sheets meet the detector's light collection requirements.

Abstract

To optimise the design of the light readout in the ArDM 1-ton liquid argon dark matter detector, a range of reflector and WLS coating combinations were investigated in several small setups, where argon scintillation light was generated by radioactive sources in gas at normal temperature and pressure and shifted into the blue region by tetraphenyl butadiene (TPB). Various thicknesses of TPB were deposited by spraying and vacuum evaporation onto specular 3M{\small\texttrademark}-foil and diffuse Tetratex{\small\textregistered} (TTX) substrates. Light yields of each reflector and TPB coating combination were compared. Reflection coefficients of TPB coated reflectors were independently measured using a spectroradiometer in a wavelength range between 200 and 650 nm. WLS coating on the PMT window was also studied. These measurements were used to define the parameters of the light reflectors of the ArDM experiment. Fifteen large $120\times 25$ cm$^2$ TTX sheets were coated and assembled in the detector. Measurements in argon gas are reported providing good evidence of fulfilling the light collection requirements of the experiment.