Reflectance and fluorescence characteristics of PTFE coated with TPB at visible, UV, and VUV as a function of thickness

TL;DR

This study investigates how the thickness of TPB-coated PTFE affects its reflectance and fluorescence at various wavelengths, finding that thickness variations between 5mm and 10mm do not significantly impact light response, enabling thinner detector components.

Contribution

It provides empirical data on the reflectance of TPB-coated PTFE across different thicknesses and wavelengths, supporting the use of thinner coatings in particle physics detectors.

Findings

Reflectance of ~92% at 450 nm for 5-10 mm thickness

Thickness variation from 5mm to 10mm has negligible effect on 128 nm light response

Thinner TPB-coated PTFE can be used without losing signal quality

Abstract

Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used in light collection systems for particle physics experiments. In noble element systems, it is often coated with tetraphenyl butadiene (TPB) to allow detection of vacuum ultraviolet scintillation light. In this work this dependence is investigated for PTFE coated with TPB in air for light of wavelengths of 200~nm, 260~nm, and 450~nm. The results show that TPB-coated PTFE has a reflectance of approximately 92\% for thicknesses ranging from 5~mm to 10~mm at 450~nm, with negligible variation as a function of thickness within this range. A cross-check of these results using an argon chamber supports the conclusion that the change in thickness from 5~mm to 10~mm does not affect significantly the light response at 128~nm. Our results indicate that pieces of TPB-coated PTFE thinner than the typical 10~mm can be used in particle physics detectors without compromising the light signal.