Simulation modelling for the analysis and the optimal design of SPAD detectors for time-resolved fluorescence measurements

This paper describes a simulation model (implemented in MATLAB®) of a typical setup used for time-resolved fluorescence measurements, including: a laser source, basic fluorescence sample, optics, single-photon avalanche diode and read-out electronics. The correctness of the model has been verified by setting up a simple time-resolved fluorescence measurement using a CMOS SPAD-based detector. The solution of fluorophore (CdSe/ZnS quantum dots in toluene) in a glass capillary was placed above the detecting surface and excited by laser pulses. We have used a timegating technique with 10-ns observation window shifted at 60-ps time steps across the appropriate time interval. The observed curve corresponds to the convolution of the fluorescence emission and the 10-ns observation window. Simulation accuracy has been verified by comparing the experimental fluorescence decay with the simulated one using chi-square test. The proposed model allows researchers to simulate the behaviour of SPAD detectors with a good accuracy and demonstrates how imperfections in the experimental system can affect the result. The model enables the design of SPAD-based detectors with the best performance for a specific application area.