K. Kuk

Focal plane detectors for Dark Energy Camera (DECam)

The Dark Energy Camera is an wide field imager currently under construction for the Dark Energy Survey. This instrument will use fully depleted 250 μm thick CCD detectors selected for their higher quantum efficiency in the near infrared with respect to thinner devices. The detectors were developed by LBNL using high resistivity Si substrate. The full set of scientific detectors needed for DECam has now been fabricated, packaged and tested. We present here the results of the testing and characterization for these devices and compare these results with the technical requirements for the Dark Energy Survey.

Cooling the Dark Energy Camera CCD array using a closed-loop, two-phase liquid nitrogen system

The Dark Energy Camera (DECam) is the new wide field prime-focus imager for the Blanco 4m telescope at CTIO. This instrument is a 3 sq. deg. camera with a 45 cm diameter focal plane consisting of 62 2k × 4k CCDs and 12 2k × 2k CCDs and was developed for the Dark Energy Survey that will start operations at CTIO in 2011. The DECam CCD array is inside the imager vessel. The focal plate is cooled using a closed loop liquid nitrogen system. As part of the development of the mechanical and cooling design, a full scale prototype imager vessel has been constructed and is now being used for Multi-CCD readout tests. The cryogenic cooling system and thermal controls are described along with cooling results from the prototype camera. The cooling system layout on the Blanco telescope in Chile is described.

The Dark Energy Survey CCD imager design

The Dark Energy Survey is planning to use a 3 sq. deg. camera that houses a ~ 0.5m diameter focal plane of 62 2k×4k CCDs. The camera vessel including the optical window cell, focal plate, focal plate mounts, cooling system and thermal controls is described. As part of the development of the mechanical and cooling design, a full scale prototype camera vessel has been constructed and is now being used for multi-CCD readout tests. Results from this prototype camera are described.

Automated characterization of CCD detectors for DECam

The Dark Energy Survey Camera (DECam) will be comprised of a mosaic of 74 charge-coupled devices (CCDs). The Dark Energy Survey (DES) science goals set stringent technical requirements for the CCDs. The CCDs are provided by LBNL with valuable cold probe data at 233 K, providing an indication of which CCDs are more likely to pass. After comprehensive testing at 173 K, about half of these qualify as science grade. Testing this large number of CCDs to determine which best meet the DES requirements is a very time-consuming task. We have developed a multistage testing program to automatically collect and analyze CCD test data. The test results are reviewed to select those CCDs that best meet the technical specifications for charge transfer efficiency, linearity, full well capacity, quantum efficiency, noise, dark current, cross talk, diffusion, and cosmetics.

Commissioning and Initial Performance of the Dark Energy Camera Liquid Nitrogen Cooling System

The Dark Energy Camera and its cooling system has been shipped to Cerro Tololo Inter-American Observatory in Chile for installation onto the Blanco 4m telescope. Along with the camera, the cooling system has been installed in the Coudé room at the Blanco Telescope. Final installation of the cooling system and operations on the telescope is planned for the middle of 2012. Initial commissioning experiences and cooling system performance is described.

Measuring the flatness of focal plane for very large mosaic CCD camera

Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty two 4k2k and twelve 2k2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and a eld of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from 2011. To achieve the science goal of constraining the Dark Energy evolution, stringent requirements are laid down for the design of DECam. Among them, the atness of the focal plane needs to be controlled within a 60-micron envelope in order to achieve the specied PSF variation limit. It is very challenging to measure the atness of the focal plane to such precision when it is placed in a high vacuum dewar at 173 K. We developed two image based techniques to measure the atness of the focal plane. By imaging a regular grid of dots on the focal plane, the CCD oset along the optical axis is converted to the variation the grid spacings at dierent positions on the focal plane. After extracting the patterns and comparing the change in spacings, we can measure the atness to high precision. In method 1, the regular dots are kept in high sub micron precision and cover the whole focal plane. In method 2, no high precision for the grid is required. Instead, we use a precise XY stage moves the pattern across the whole focal plane and comparing the variations of the spacing when it is imaged by dierent CCDs. Simulation and real measurements show that the two methods work very well for our purpose, and are in good agreement with the direct optical measurements.

Surface cleaning of CCD imagers using an electrostatic dissipative formulation of first contact polymer

We describe the results obtained cleaning the surface of DECam CCD detectors with a new electrostatic dissipative formulation of First ContactTM polymer from Photonic Cleaning Technologies. We demonstrate that cleaning with this new product is possible without ESD damage to the sensors and without degradation of the antireflective coating used to optimize the optical performance of the detector. We show that First ContactTM is more effective for cleaning a CCD than the commonly used acetone swab.