Photon Film

Single-Photon Avalanche Diode (SPAD) sensors are ultra-sensitive semiconductor devices capable of detecting individual photons with picosecond temporal precision, making them invaluable for imaging phenomena at extremely fast timescales.

Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) have pioneered their use in ultrafast imaging systems—such as the "MegaX" and "SwissSPAD2" cameras—which operate by biasing each diode above its breakdown voltage so that the absorption of a single photon triggers a self-sustaining avalanche of charge carriers.

This avalanche is then rapidly quenched and reset, allowing frame rates of up to 1 trillion frames per second when paired with time-correlated single-photon counting (TCSPC) techniques.

Arrays of SPADs can reconstruct light propagation, effectively visualizing photons as they move through scattering media or reflect around corners—a technique known as non-line-of-sight imaging.

EPFL’s systems use CMOS-compatible fabrication, enabling large-scale SPAD arrays with nanosecond gating and low dark-count rates, providing breakthroughs in fields from biomedical fluorescence lifetime imaging to autonomous vehicle LiDAR and quantum optics.