Current students

The analysis of fast and faint optical pulses is gaining a major role in different fields ranging from biology (fluorescence decay and single-molecule analysis), to communication (quantum cryptography) and laser ranging (LIDAR). In this framework, Time-Correlated Single Photon Counting (TCSPC) is a very sensitive method that consists in the periodical stimulation of a sample with a pulsed laser and in the collection of re-emitted photons.With the evolution and development of innovative techniques, many applications are nowadays demanding for real-time acquisition with a significant increase of the required measurement rate. However, to prevent classical pile-up distortion, typical TCSPC measurements should be carried out reducing the average number of impinging photons well below 5% of the excitation rate (i.e. 4 Mcps with a typical 80 MHz laser). This phenomenon constitutes, therefore, a significant limitation to the maximum achievable speed. 

To avoid this issue, current state-of-the-art systems typically employ a multichannel approach, where more pixels are acquired in parallel. Nevertheless, even in this case each channel must obey to the 5% limitation. It is therefore desirable to identify a more radical solution to the problem. In recent years, it has been demonstrated that by matching the detector dead time to the laser period no distortion is obtained even at extremely high rates. However, the transition between the theoretical idea and the practical implementation of the novel technique poses many challenges both from the integrated and overall system point of views. 

This research project aims at overcoming the historical pile-up limitation, by designing and deeply characterizing the first prototype module that implements the proposed technique. To achieve such an ambitious result, the problem will be analyzed under several aspects. For example, the non-idealities of the integrated front-end electronics will be taken into account as a possible cause of imperfect dead time matching. Moreover, a Fast Time to Amplitude Converter (F-TAC) will be designed and integrated into the system to achieve a 40 Mcps measurement rate along with the finest precision. 

The developed concept will then be extended to a multichannel system, thus definitely breaking the classical trade-off between speed and distortion. In this way a single optimized channel will be replicated many times, achieving an ultrafast TCSPC system. Besides speed requirements, all the channels should also grant excellent performance in terms of Differential NonLinearity (few percents), timing precision (lower than 10 ps), crosstalk, compactness and portability. In this scenario, considerable importance will be equally attributed to high-speed data links between the system and the host PC, to manage the huge amount of data generated by TCSPC experiments.