Sensors enable first light for the Dark Energy Camera
18 September 2012
On September 12, the Dark Energy Camera (DECam), mounted on the Victor Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile, recorded its first images.
Galaxies up to eight billion light years away were captured on DECam’s focal plane, whose imager consists of 62 charge-coupled devices (CCDs) developed by engineers and physicists at the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).
Berkeley Lab CCDs are noted for their exceptionally high sensitivity to light (quantum efficiency), particularly in the red and infrared regions of the spectrum – a crucial advantage for astronomical CCDs searching for objects at extremely high redshifts. Combining the 570-million-pixel focal plane comprising the CCDs with the light-gathering power of the Blanco telescope’s 4m mirror, DECam has the ability to reach wide and deep into the night sky.
DECam was built by the Dark Energy Survey (DES) collaboration based at the Fermi National Accelerator Laboratory. A photometric imaging camera, it measures the amount of light in various colours from astronomical objects rather than details of their spectra. DECam’s goal is to measure the expansion history of the universe by collecting images of 4,000 distant supernovae and 300 million distant galaxies within the next five years.
The manufacturing process
The DECam chips were fabricated by Berkeley Lab’s industrial partner, Teledyne DALSA Semiconductor, and the Physics Division’s MicroSystems Laboratory. Partially finished wafers holding four CCDs, each with eight of eleven masking steps completed, were commercially thinned, then sent to the MicroSystems Laboratory for completion. “Cold-probe” tests at minus 45 degrees Celsius were performed to detect shorts, defects, and excessive dark current. The CCDs were cut from the wafer and sent to Fermilab for mounting and final testing.
“In the first months, manufacturing went slowly,” Roe says, “but we used data from each lot of wafers to feed back processing improvements, and the yield steadily improved. We used conservative estimates and overshot the requirements – at the end, we produced twice as many science-grade CCDs as needed.”
DECam will produce the largest-ever 3D map of the universe, a record currently held by the third Sloan Digital Sky Survey and its largest component, the Baryon Oscillation Spectroscopic Survey (BOSS), led by Berkeley Lab astrophysicists. The red channel of the SDSS-III spectrograph, whose development was led by Roe, also uses Berkeley Lab CCDs.