Increasing the count rate of time-correlated single photon counting techniques with immersion lenses on single photon avalanche diodes

We demonstrate the benefits of affixing a high index hemispherical immersion lens on the photosensitive surface of single photon avalanche diodes (SPADs) for time-correlated single photon counting (TCSPC). The goal of this work was to increase the photon counting rate of a non-contact time-domain diffuse optical tomography (TD-DOT) scanner for intrinsic and fluorescence measurements. Zemax simulations have also been carried out and are in good agreement with the experimental data. We believe that this technology can also be used in other applications of TCSPC such as microscopy.