Tiny 'on-chip detectors' count individual photons

Washington, D.C. (March 17, 2011) -- A team of researchers has integrated tiny detectors capable of counting individual photons on computer chips. These detectors, called "single-photon avalanche diodes (SPAD)," act like mini Geiger counters, producing a "tick" each time a photon is detected.

The researchers present their findings in Applied Physics Letters, a journal published by the American Institute of Physics.

"In the past, making these detectors required specialized processes, but recently there has been tremendous progress in making these devices in 'standard' integrated circuit processes—those used to make computer chips," says Ryan Field, a Ph.D. candidate in the department of electrical engineering at Columbia University. "This has dramatically decreased the cost of making detectors and enabled them to be integrated on the same chip with complex circuitry."

The team has produced such detectors with extremely low noise, which means that there's a low probability of getting a 'tick' without a photon present.

"These detectors are being used for specialized camera chips to measure fluorescence, which is extremely important to biological imaging," explains Field. "Fluorescent labels are used throughout biology to image processes in vivo and in vitro. One of the properties of fluorescence is that it decays after the excitation source has been removed, with a characteristic decay time known as the 'lifetime.' By photon counting, we can measure this lifetime with our SPAD-based camera, forming a high-frame-rate lifetime imager that can provide further insight into the nature of biological processes."

Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics. Emphasizing rapid dissemination of key data and new physical insights, Applied Physics Letters offers prompt publication of new experimental and theoretical papers bearing on applications of physics phenomena to all branches of science, engineering, and modern technology. Content is published online daily, collected into weekly online and printed issues (52 issues per year). See: http://apl.aip.org/

The American Institute of Physics is a federation of 10 physical science societies representing more than 135,000 scientists, engineers, and educators and is one of the world's largest publishers of scientific information in the physical sciences. Offering partnership solutions for scientific societies and for similar organizations in science and engineering, AIP is a leader in the field of electronic publishing of scholarly journals. AIP publishes 12 journals (some of which are the most highly cited in their respective fields), two magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. Its online publishing platform Scitation hosts nearly two million articles from more than 185 scholarly journals and other publications of 28 learned society publishers.