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  • Camera Overcomes Redshift for Astronomical Imaging

Photonics.com
Feb 2016
BERKELEY, Calif., Feb. 9, 2016 — Upgraded light sensors have enabled a camera to image outer space at red wavelengths that are too red for the human eye to see.

Star trails take shape around Kitt Peak National Observatory in this long-exposure image. The 4-m Mayall Telescope building, at right, now houses Mosaic-3, an IR camera. Courtesy of P. Marenfeld, NOAO/AURA/NSF. 
Due to an effect known as redshift, very distant astronomical objects appear much redder when observed on Earth. The camera’s sensitivity to red light enables it to detect objects many billions of light years away.

The light sensors were developed at the U.S. Department of Energy's Lawrence Berkeley National Laboratory, and the camera system resulted from the combined efforts of scientists from Berkeley Lab, Yale University and the National Optical Astronomy Observatory (NOAO).

Dubbed Mosaic-3, the rebuilt camera has begun its two-year mission to survey the sky, amassing images of hundreds of millions of galaxies and stars. Installed in October on the 4-meter Mayall Telescope at Kitt Peak National Observatory near Tucson, Ariz., Mosaic-3 will survey the northern sky at IR wavelengths from 850 nm to 1 μ — a range known as the z-band — and will capture images nearly twice as fast as its predecessor camera, the reasearchers said.

In addition to incorporating the new sensors, the camera features a refurbished and replacement electronics.

"We rebuilt the whole camera," said Yale professor Charles Baltay. "We started in early February and delivered it in August — we had to hustle. At first, people said we couldn't do it this fast. Mosaic-3 can measure the same object in half the time compared to its predecessor. It allows us to do the target-selection survey in time — it moves it from impossible to comfortable."

The piece of glass used as Mosaic-3's filter for gathering IR light appears perfectly black to the naked eye but transmits 98 percent of the incoming IR light at the wavelengths it is scanning.

Berkeley Lab supplied the CCDs that capture light and the readout system that translates the light into images. Yale was responsible for mechanical components and software, working closely with NOAO astronomers and engineers on the latter.

Mosaic-3 is equipped with four CCDs, each measuring about 6 in.2 and containing 16 MP. Each pixel in the CCDs is about 100 times larger in area than a pixel in an iPhone 6 camera sensor, and each Mosaic-3 CCD is about 50 times larger in area than the iPhone 6 camera sensor.

"It's really the light-gathering power that matters," said Berkeley design engineer Armin Karcher, who built a compact, flexible readout system for the camera.

The large pixel size and overall CCD size are key in gathering light, and the 0.5-mm thickness of the CCDs helps the CCDs see deeper into the IR wavelengths.

The instrument upgrade was funded by the U.S. Department of Energy Office of Science through the DESI project and by NOAO. The DESI project is managed by the Lawrence Berkeley National Laboratory.


GLOSSARY
astronomy
The scientific observation of celestial radiation that has reached the vicinity of Earth, and the interpretation of these observations to determine the characteristics of the extraterrestrial bodies and phenomena that have emitted the radiation.
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