Distributed time resolved fluorescence sensor using temporally correlated photons

A method of measuring fluorescence, comprising:

• outputting pairs of entangled photons from a continuous wave source;
• splitting, at a splitter, each of the pairs into a first photon and a second photon;
• transmitting the first photon through a first channel or arm to a first detector;
• transmitting the second photon, in a second arm or channel, to a sample comprising an excited state to generate an output photon;
• detecting the first photon at the first detector and the output photon at a second detector;
• for each of a plurality of detection events associated with a plurality of pairs of the entangled photons and each comprising a first arrival time of the first photon at the first detector and a second arrival time of the output photon (generated by the second photon paired with the first photon) at the second detector:
• measuring a time delay between the first arrival time and the second arrival time;
• counting a number of detection of events to obtain statistical data comprising a frequency of the time delays;
• and
• determining a fluorescence lifetime of the excited state from the statistical data.