Objectives

• large active area of the SPAD pixels (diameter between 50µm and 100µm);
• high photon detection efficiency in the visible and near infra-red spectral range (~ 50% at 550 nm, ~ 25% at 700nm);
• low dark counting rate ( < 1000c/s with detector chip at room temperature, <50c/s with chip cooled by an integrated Peltier element);
• low afterpulsing (total afterpulsing probability < 3%);
• good photon timing resolution ( ~ 100ps FWHM or better);
• low optical crosstalk probability (< 1%).
In this context, POLIMI and CNR (RTD performers) will carry out the main research activity; MPD (SME participant) will contribute and provide the final engineering of the detector prototype. A linear 8x1 SPAD array will be developed. The array will be housed in a compact photon counting module, which will include all the electronics needed for the operation of the individual SPADs in the array, the bias supply distribution and the cooling of the detector chip by means of a Peltier element. b) reproducible micro-lens system for focusing light onto every SPAD pixel. The micro-optical sub-system will provide:
• A higher effective fill factor on each pixel, improving overall detector efficiency.
• Suitable AR coatings on each surface to improve efficiency and reduce back- reflections.
• A form of mechanical assembly for robust and reproducible prototypes. 
• Investigation into dichroic or bandpass filters for deposition on both the SPAD array surface and/or on the micro-lens for maximum fluorescence transmission and rejection of stray light.
In this context, HWU (RTD performer) will carry out the main research activity; HPL (SME participant) will contribute and provide the engineering of the setup. c) Optoelectronic setup with confocal microscope and ASIC based multichannel integrated time correlated single photon counting (TCSPC) system providing:
• 8 fully-parallel input channels for TCSPC; 
• short dead-time, typically <20ns, allowing high measurement rates (several MC/s);
• time-to-digital converter with minimum channel width on the order of 20ps;
• time-tagged time-resolved (TTTR) operation mode, enabling recording of individual count events directly to hard disk or computer memory. The timing of each photon is captured as an event record without any early data reduction (such as on-board forming of histograms). This operation mode enables the implementation of virtually all known methods based on the measurement of single photon dynamics like fluorescence correlation spectroscopy (FCS), online lifetime monitoring and fluorescence lifetime imaging (FLIM).
• 8 channel demonstrator system, with the 8x1 SPAD array incorporated into the leading single molecule microscopy system MT200 of PicoQuant for demonstrating the advantage and practical importance of the fully parallel detection. Although 1-spot excitation and 8-channel detection for sFLIM will be targeted as the main goal, some exploratory work will also be done looking to other possible applications; for instance, work on 8-spot excitation and detection optics for a fully parallel fluorescence correlation spectroscopy.