Characterization of UV optical components for photon detector calibration in liquid argon TPCs

TL;DR

This paper evaluates and characterizes UV optical components for calibration systems in liquid argon TPCs, demonstrating their stability, efficiency, and suitability for large-scale cryogenic detectors like DUNE.

Contribution

It provides comprehensive measurements of UV optical components' performance and durability under cryogenic conditions, informing their selection for large-scale detector calibration.

Findings

Optical components show no significant degradation after thermal cycling.

Fiber and connector losses are characterized across 275-970 nm wavelengths.

Diffuser assemblies provide uniform Lambertian emission.

Abstract

Large liquid argon time projection chambers (LArTPCs) require stable and well-characterized delivery of ultraviolet (UV) light for in situ calibration of photosensors at cryogenic temperatures. This article reports bench-top and cryogenic measurements of the optical components used in a UV light calibration system, including multi-mode fused-silica fibers, SMA-to-SMA connectors, optical fiber feedthroughs, and light-diffuser assemblies. Light loss in several fiber types and SMA connectors was measured across wavelengths from \qtyrange{275}{970}{nm}. In addition, light-loss measurements of the tested fibers after several liquid-nitrogen thermal cycles showed no statistically significant degradation relative to baseline measurements, and high-rate pulsed exposure (30-90 million pulses from a \qty{275}{nm} LED) likewise showed no measurable aging in jacketed fibers. A compact, palm-sized, 3D-printed PEEK diffuser housing with stacked UV-grade fused-silica diffusers yields Lambertian emission and the most uniform angular distribution. Optical components exhibiting improved UV transmission were deployed successfully in multiple DUNE small- and large-scale prototypes, demonstrating reliable operation of UV light calibration systems. These findings inform component selection and calibration procedures for achieving reliable, uniform UV light delivery in large-scale cryogenic detectors such as DUNE.