Nano-device tracks single photons

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Photo by Urska Kosir.

A new device may allow NASA telescopes to analyze light from distant galaxies billions of lightyears away, starting in a decade or two.

Researchers at Yale and NASA’s Jet Propulsion Laboratory have developed a new “nanobolometer” that can isolate single photons of infrared light, revealing traits of the most distant galaxies. It is the most accurate device of its type ever created, but since it can only serve its intended purpose on a space telescope, and NASA has no current missions that could include the device, the project’s researchers say it is unlikely their work will be implemented within a decade. It will also take a number of years before the current prototype can be scaled up into a workable sensor, said Boris Karasik, a NASA researcher.

Daniel Prober, professor of applied physics and physics at Yale, said the device is the smallest to measure photons accurately in the relatively faint range of infrared light. Prober’s results were invited to the published in the inaugural issue of IEEE Transactions on Terahertz Science and Technology, a new scientific journal, this September. The device’s titanium frame is between 1000 and 100 times smaller than the diameter of a human hair, said Daniel Santavicca GRD’09, a postdoctoral researcher at Yale who worked with Prober on the device.

“Our results said that the [device] is as promising as the theory predicted,” Probersaid.

The device absorbs individual photons as heat, measures the increase in energy, and then extrapolates backwardto find the original energy level of the photon, Santavicca said. Scientists can then usethe device’s results to reveal the nature of the original light source.

The new device would help research into distant galaxies, which Prober said was one of the less-understood realms of astronomy. Galaxies with different chemical composition would give off different forms of light, which scientists could use to understand how they form, Prober said. Since light from the farthest galaxies can take billions of years to reach Earth, scientists observing that light are able to look at those galaxies in their earliest stages.

“This has been a continuing goal of space scientists, but until these detectors, there hadn’t been the means to do that,” Prober said.

Previous nanobolometers have measured infrared light by detecting several photons at once and averaging their energy, but this process is much less accurate and affected by unpredictable variation to a greater degree, said James Bock, a principal scientist at the Jet Propulsion Laboratory, in Pasadena, Calif., who was not a part of the research team.

The new device comes after decades of research by co-authors Prober and Karasikand others, which had previously remained somewhat theoretical. Prober said he published a theoretical paper on the subject in 1993, and Karasik said he has received about nine years of NASA funding towards this specific project.

Karasik experimented by shooting single photons at the nanobolometer at the Jet Propulsion Laboratory, where he works as a principalresearch technologist, and found that it was more accurate than any previous attempts.

Prober’s team verified the results of Karasik’s research at Yale with pulses of microwave radiation, closely confirming their results with only a slight discrepancy, Prober said. He added that his laboratory would run experiments to account for the discrepancy. Santavicca said they have fabricated dozens of new nanobolometers with tiny antenna that they say should be able to catch just one photon at a time without being affected by extraneous photons.

Prober and Santavicca said one of the greatest challenges in testing a device so small is that any disruption from light and heat can alter the measurement. This means that to test the instrument properly, researchers need to cool the device to a few degrees above absolute zero, Santavicca said.

The nanobolometer may have some applications in chemistry in extremely cold environments, but was primarily conceived to be useful in space, Karasik and Prober said.

Karasik said that researchers at the Jet Propulsion Lab have expressed interest in finalizing the new device in time for a Japanese SPICA space telescope, whose projected launch date is 2017. But Karasik added it was unlikely the device would be ready in time. The main obstacles lay in scaling up the device from one tiny sensor to hundreds of them able to all operate accurately, and testing the device in more realistic environments, Karasik said.

It takes about a day to cool the device to near absolute zero, Santavicca said.

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