A. Fukasawa

Characterization of the QUartz Photon Intensifying Detector (QUPID) for Noble Liquid Detectors

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 QUPIDs from the first production line. Screening of radioactivity at the Gator facility in the Laboratori Nazionali del Gran Sasso has shown that the QUPIDs 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 low temperatures, the QUPID shows a leakage current less than 1 nA and a global gain of 10^5. In these conditions, the photocathode and the anode show > 95% linearity up to 1 uA 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 QUPIDs have a good timing response: 1.8 +/- 0.1 ns rise time, 2.5 +/- 0.2 ns fall time, 4.20 +/- 0.05 ns pulse width, and 160 +/- 30 ps transit time spread. The QUPIDs have also been tested in a liquid xenon environment, and scintillation light from 57Co and 210Po radioactive sources were observed.

High Speed HPD for Photon Counting

We have succeeded in the development of a high-speed Hybrid Photodetector (HPD), by using a reduced electron lens and a newly developed avalanche diode (AD) with very low capacitance. The HPD shows fast time response of less than 500 ps in both rise and fall times, and good timing resolution of 26 ps (one sigma) for single photons at full illumination on a photocathode 8 mm in diameter. Limiting factors of the timing resolution were further investigated, and were found to be the transit time difference of electrons in vacuum along the photocathode and the jitter of the electronics. The timing resolution is 15 ps for illumination of less than 5 mm on the central part of the photocathode, which includes the jitter of 13 ps from the electronics. This resolution is the worlds highest for HPDs, and matches the resolution of MCP-PMTs. Both a GaAsP photocathode having close to 50% quantum efficiency in the visible and a bialkali photocathode having 34% QE in the UV were fabricated in view of making this device available for various applications. In this paper, we report the results of our evaluation, including discussion about the limiting factors of the timing resolution for the new HPD.

Development of a multi-pixel hybrid photodetector with high quantum efficiency and gain

A hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel avalanche diode (MP-AD) has been developed for these years. One of the features of the HPD is a good energy resolution, and it was shown in our previous study that the further improvement would be possible by reducing the fluctuation of charge loss in the dead layer at the entrance of the MP-AD. In this paper, we report on the result of the improvement with the newly developed HPD whose MP-AD encapsulated has a thinner dead layer than before. It is demonstrated that the new HPD has a much better energy resolution which enables the clear counting up to nine photoelectrons. Other features like a uniformity among the pixels or a photocathode sensitivity of the HPD are also presented.A hybrid photodetector (HPD) consisting of a photocathode and a multipixel avalanche diode (MP-AD) was developed a few years ago. Our previous studies showed that its inherent potential for high resolution photon counting could be further enhanced by reducing fluctuations in charge loss in the dead layer at the entrance of the MP-AD. In this paper, we report on the improvement with the newly developed HPD whose encapsulated MP-AD has a thinner dead layer than before. It is demonstrated that the new HPD has much better energy resolution, which enables clearer counting up to nine photoelectrons. Further enhancement of the photocathode sensitivity of the HPD is also discussed.

High-performance HPD for photon counting

We have developed a new Hybrid Photo-Detector (HPD) with relatively large effective area, fast time response, high timing resolution, high quantum efficiency and extremely low probability of afterpulse. A GaAsP (Gallium Arsenide Phosphide) photocathode type has high quantum efficiency approximately 45% around the wavelength of 500 nm, and the size of the effective area is 3 mm in diameter. The pulse height for single photon is approximately +2 mV with 50 ohm load impedance, and it can be easily observed with a fast response oscilloscope. The rise and fall times for impulse light are approximately 0.4 ns. The timing resolution for single photon for the GaAsP photocathode type was estimated to be approximately 80 ps.