First demonstration of THGEM/GAPD-matrix optical readout in a two-phase Cryogenic Avalanche Detector in Ar

The multi-channel optical readout of a THGEM multiplier coupled to a matrix of 3×3 Geiger-mode APDs (GAPDs) was demonstrated in a two-phase Cryogenic Avalanche Detector (CRAD) in Ar. The GAPDs recorded THGEM-hole avalanches in the Near Infrared (NIR) spectral range. At an avalanche charge gain of 160, the yield of the combined THGEM/GAPD-matrix multiplier amounted to ~80 photoelectrons per 20 keV X-ray absorbed in the liquid phase. A spatial resolution of 2.5 mm (FWHM) has been measured for the impinging X-rays. This technique has potential applications in coherent neutrino-nucleus scattering and in dark matter search experiments.