Scientists have developed tiny detectors, referred as single-photon avalanche diodes (SPAD), for counting individual photons on a computer chip. These tiny devices generate a tick sound every time, when they detect a photon and hence, their performance is similar to mini Geiger counters.
A Ph.D. candidate at Columbia University, Ryan Field explains that earlier, there was s a need for specialized processes to produce these tiny detectors or SPADs. But, now it is easy with recent advancements. The detectors can be produced using integrated circuit processes that are used for computer chip production. This recent progress has significantly reduced the cost for developing SPADs, as well as facilitates easier integration of the tiny devices on complex circuitry-based chips.
Researchers have thus developed tiny on-chip detectors with low noise. This means, if a photon is not present, there is less chance of getting a tick.
The newly produced photon counting devices are integrated on specialty camera chips for measuring fluorescence. Fluorescent labels play a major role in biological imaging processes, in vitro and in vivo. Fluorescence gets decayed, once the excitation source is removed and the decay time is called lifetime. With the help of the SPAD-integrated camera, lifetime of fluorescence can be measured by photon counting. Thus, the imager can offer additional insight into the biological processes.
Source: http://www.aip.org/