VUV Reflectance Measurements for Materials Relevant to Argon and Xenon Experiments

TL;DR

This study develops a specialized measurement system to accurately determine the VUV reflectance of materials used in noble gas detectors, revealing lower reflectance values than in the UV-VIS range and informing detector design.

Contribution

We introduce a novel angular-resolved reflectance measurement system operating in gaseous argon, providing realistic VUV reflectance data for detector materials under controlled conditions.

Findings

Confirmed literature values of ~60% reflectance for aluminum in UV-VIS.

Measured 10-15% reflectance for aluminum and stainless steel in VUV at 45° incidence.

Reflected light shows a mix of specular and diffuse reflection.

Abstract

Accurate knowledge of material reflectance in the vacuum ultraviolet (VUV) range is crucial for optimizing photon detection in noble gas detectors such as DUNE. Despite its importance, reflectance values for detector materials in the VUV region remain poorly characterized, with literature values showing significant variation depending on surface termination and finish. We present an angular-resolved reflectance measurement system developed at IFIC that operates in a gaseous argon atmosphere, enabling realistic measurements of detector materials under controlled conditions. The setup couples a deuterium lamp to a monochromator and employs a motorized PMT rotating around the sample to measure reflected light distributions across a wide angular range. We have characterized two key DUNE materials -- aluminum field cage profiles and stainless steel cryostat membranes -- in both the UV-VIS (300-500 nm) and VUV (128-200 nm) ranges. In the UV-VIS region, we confirm literature values of approximately 60% reflectance for aluminum and 40% for stainless steel. Preliminary VUV measurements at 45{\deg} angle of incidence yield reflectance values of 10-15% for both materials, significantly lower than their UV-VIS counterparts. The reflected light distributions exhibit a mixed character between specular and diffuse reflection. These results have direct implications for detector simulations and light yield predictions in next-generation experiments.