Dark Matter and Double Beta Decay experiments require extremely low radioactivity within the detector materials .
For this purpose , the University of California , Los Angeles and Hamamatsu Photonics have developed the QUartz Photon Intensifying Detector ( Qupid ) , an ultra-low background photodetector based on the Hybrid Avalanche Photo Diode ( HAPD ) and entirely made of ultraclean synthetic fused silica .
In this work we present the basic concept of the Qupid and the testing measurements on Qupid s from the first production line .

Screening of radioactivity at the Gator facility in the Laboratori Nazionali del Gran Sasso has shown that the Qupid s safely fulfill the low radioactive contamination requirements for the next generation zero background experiments set by Monte Carlo simulations .

The quantum efficiency of the Qupid at room temperature is > 30 % at the xenon scintillation wavelength .
At -100 ^ { \circ } C , the Qupid shows a leakage current smaller than 1 nA and a global gain of 10 ^ { 5 } .
In these conditions , the photocathode and the anode show > 95 \% linearity up to 1 ~ { } \mu A for the cathode and 3 mA for the anode .
The photocathode and collection efficiency are uniform to 80 % over the entire surface .
In parallel with single photon counting capabilities , the Qupid s have a good timing response : 1.8 \pm 0.1 ns rise time , 2.5 \pm 0.2 ns fall time , 4.20 \pm 0.05 ns ( FWHM ) pulse width , and 160 \pm 30 ps ( FWHM ) transit time spread .

The Qupid s have also been tested in a liquid xenon environment , and scintillation light from ^ { 57 } Co and ^ { 210 } Po radioactive sources were observed .