First measurement of scintillation photon arrival statistics using a high-granularity solid-state photosensor enabling time-stamping of up to 20,480 single photons

We propose a novel experimental method using a single-photon avalanche diode and time-to-digital convertor (SPAD-TDC) array that, for the first time, enables simultaneous measurement of the spatial and time dependence of the arrival of optical photons in a scintillation pulse with high resolution (tunable between 55 and 100 ps in time, 50 μm in space). By registering all available timing information contained in a scintillation pulse, this method should make it possible to study and develop new time-stamping techniques based on experimental data. In this paper, we present a proof-of-concept of the method including the first results obtained with a 3 mm × 3 mm × 5 mm LYSO:Ce crystal. The crystal is placed on a SPAD-TDC array consisting of 160 × 128 micropixels in total. Every micropixel consists of a SPAD and a 10 bit TDC, thus each individual avalanche (triggered by a photon) can be time-stamped. A fs-UV-laser is used to excite the crystal at a wavelength of 360 nm with a pulse repetition rate of 1.9 MHz. Scintillation photons are measured with a TDC resolution of 84 ps (1 LSB). The overall single-photon timing resolution, or jitter, was found to be equal to 265 ps FWHM. Our first results indicate the potential of this setup in delivering insight into scintillation counting statistics, both in space and time.