Vacuum ultraviolet high-reflectance aluminum mirrors on copper substrate for application in noble liquid time projection chamber

Abstract

Enhancing vacuum ultraviolet reflection at surface of Cu electrode is key to obtain sufficient photon collection efficiency in noble liquid time projection chamber. In this work, MgF2-overcoated Al mirrors is utilized to realize the desired high reflectivity for scintillation photons of liquid xenon at 175 nm. Thermal evaporation technique is explored for the mirror preparation. The Al mirror deposited directly on Cu substrate suffers from severely absorptive and scattering losses and yields 30.3% reflectivity due to the formation of Cu–Al alloy. By prior deposition of a SiO2 intermediate layer on the Cu substrate, the alloy process is prevented and the absorptive loss is suppressed by a factor of 4 approximately. The highest reflectance 82.1% is obtained through optimizing the thickness of the SiO2 intermediate layer. The work holds potential to improve the capability of noble liquid time projection chambers for detection of dark matter and neutrinoless double beta decays.