Time-correlated single photon counting (TCSPC) underlies technologies such as fluorescence lifetime microscopy (FLIM) and time-of-flight (ToF) 3D imaging, and can be precise enough to time the detection of photons emitted from an excited sample just a few picoseconds apart. Pushing the capabilities of TCSPC into the femtosecond range can allow for even more advanced imaging using these technologies. A team of researchers at the University of Colorado Boulder have developed a new method to enable this unprecedented timing resolution by equipping a single-photon detector with a “time lens” to magnify the abilities of TCSPC.
TCSPC counts photons as they hit the single-photon detector and times the arrival of each photon, like an extremely precise quantum “stopwatch.” However, the detector may register more than one photon as just one if they arrive at the sensor less than a few picoseconds apart. The time lens developed by the researchers, made up of loops of silica fibers, magnifies the gap between photons as they pass through it before reaching the detector, enabling the counting of photons just hundreds of femtoseconds apart. The team applied their quantum temporal magnification technique to ToF 3D imaging, showing that it produced a much clearer image than conventional TCSPC. This research was published in Optica.
“In a microscope, we use optical lenses to magnify a small object into a big image. Our time lens works in a similar way but for time,” said lead author Bowen Li.
The study authors wrote that they believe their enhanced TCSPC technique could possibly bring femtosecond-range photon counting to applications including not only ToF 3D imaging, but also fluorescence lifetime microscopy, time-gated Raman spectroscopy, light-in-flight imaging, computational diffuse optical tomography and lidar.