The laser confocal microscope (LCM) is now an established research tool in biology and materials science. In biological applications, it is usually employed to detect the location of fluorescent marker molecules and, under these conditions, detected signal levels from bright areas often represent <20 photons/pixel (assuming a standard 1.6 μs pixel time) while those from dark areas are likely to average <1 photon/pixel. Although this data rate limits the speed at which information can be derived from the specimen, saturation of the fluorophor, photobleaching of the dye, and phototoxicity often prevent it being increased by simply using more laser power. Over the past 10 years, the optical photon efficiency of commercial confocal instruments has improved significantly and it is now reaching the point where further improvement is becoming very expensive. The only component is which a significant improvement is still possible is the photodetector.
Detecting an Itinerant Optical Photon Twice without Destroying It
