Single-photon avalanche photodiode (SPAD) image sensors offer time-gated photon counting, at high binary frame rates of >100 kFPS and with no readout noise. This makes them well-suited to a range of scientific applications, including microscopy, sensing and quantum optics. However, due to the complex electronics required, the fill factor tends to be significantly lower (< 10%) than that of EMCCD and sCMOS cameras (>90%), whilst the pixel size is typically larger, impacting the sensitivity and practicalities of the SPAD devices. This paper presents the first characterisation of a cylindrical-shaped microlens array applied to a small, 8 micron, pixel SPAD imager. The enhanced fill factor, ≈50% for collimated light, is the highest reported value amongst SPAD sensors with comparable resolution and pixel pitch. We demonstrate the impact of the increased sensitivity in single-molecule localisation microscopy, obtaining a resolution of below 40nm, the best reported figure for a SPAD sensor.
- Photon counting
- Fluorescence microscopy
- Avalanche photodiodes (APDs)
- Micro-optical devices
Gyongy, I., Davies, A., Gallinet, B., Dutton, N. A. W., Duncan, R. R., Rickman, C., Henderson, R. K., & Dalgarno, P. A. (2018). Cylindrical microlensing for enhanced collection efficiency of small pixel SPAD arrays in single-molecule localisation microscopy. Optics Express, 26(3), 2280-2291. https://doi.org/10.1364/OE.26.002280