Attenuation of vacuum ultraviolet light in liquid argon

TL;DR

This study measures how liquid argon transmits vacuum ultraviolet light across 118-250 nm, revealing wavelength-dependent absorption features and impurity effects, crucial for applications in particle detection.

Contribution

It provides detailed wavelength-resolved attenuation lengths for pure and impure liquid argon, highlighting impurity effects on VUV transmission, which was not comprehensively characterized before.

Findings

No universal wavelength-independent attenuation length exists for liquid argon.

Impurities like xenon and water significantly affect transmission, with specific absorption bands identified.

Transmission decreases below 130 nm due to argon excimer absorption.

Abstract

The transmission of liquid argon has been measured, wavelength resolved, for a wavelength interval from 118 to 250 nm. The wavelength dependent attenuation length is presented for pure argon. It is shown that no universal wavelength independent attenuation length can be assigned to liquid argon for its own fluorescence light due to the interplay between the wavelength dependent emission and absorption. A decreasing transmission is observed below 130 nm in both chemically cleaned and distilled liquid argon and assigned to absorption by the analogue of the first argon excimer continuum. For not perfectly cleaned argon a strong influence of impurities on the transmission is observed. Two strong absorption bands at 126.5 and 141.0 nm with approximately 2 and 4 nm width, respectively, are assigned to traces of xenon in argon. A broad absorption region below 180 nm is found for unpurified argon and tentatively attributed to the presence of water in the argon sample.