Photon counting

However, if it is known that a single photon was detected, the center of the impulse response can be evaluated to precisely determine its arrival time.

Single-photon detection is useful in fields such as:[1] In radiology, one of the major disadvantages of X-ray imaging modalities is the negative effects of ionising radiation.

One way of reducing exposures is to make X-ray detectors as efficient as possible, so that lower doses can be used for a given diagnostic image quality.

[12] Photon-counting computed tomography is another interest area, which is rapidly evolving and is approaching clinical feasibility.

[13][14][15][16] Time-correlated single-photon counting (TCSPC) precisely records the arrival times of individual photons, enabling measurement of picosecond time-scale differences in the arrival times of photons generated by fluorescent, phosphorescence or other chemical processes that emit light, providing additional molecular information about samples.

The use of TCSPC enables relatively slow detectors to measure extremely minute time differences that would be obscured by overlapping impulse responses if multiple photons were incident concurrently.

Some pulse LIDAR systems operate in single photon counting mode using TCSPC to achieve higher resolution.