Development of a multi-pixel photon sensor with single-photon sensitivity

A multi-pixel photon sensor with single-photon sensitivity has been developed. Based on a hybrid photo-detector (HPD) technology, it consists of a photocathode and a multi-pixel avalanche diode (MP-AD). The developed HPD has a proximity-focused structure, where the photocathode and MP-AD face each other with a small gap of 2.5 mm. The MP-AD, which has an effective area of 16 mm×16 mm, is composed of 8×8 pixel and has been specially designed for the HPD. The maximum gain of the HPD is 5×104, sufficiently high to detect single photons with a timing resolution better than 100 ps. Up to four photoelectrons can be clearly identified as distinct peaks in a pulse-height spectrum, thanks to the low-noise characteristics of the HPD. It is also demonstrated that the HPD can be operated with good performance in a magnetic field as high as 1.5 T.