Technical CCD Systems for the ESO Very Large Telescope [chapter]

J. Ehrich
1995 New Developments in Array Technology and Applications  
The Technical CCD Systems (TCCDS) consist of thermo-electrically cooled CCD detector heads together with the electronic hardware and software for the control of the CCD and readout of the data. Two different types of CCD heads equipped with a small and a large format CCD chip are used. The small format CCD systems will be used primarily for auto-guiding and field acquisition at the main foci of the VLT. The large format CCD systems are intended mainly for wavefront sensing applications. An
more » ... plications. An overview of the primary modes of operation of the TCCDS and the corresponding fields and exposure conditions for these modes is given in Table 1 . The term "Technical CCD Systems" is derived from the intended application in the VLT because due to the excellent CCD head parameters and the system performance a scientific application will be offered too. TABLE 1 Primary modes of operation CCD Format small small large Operational Mode acquisition mode Field Size 1 arc min Wavelength 400 -1000 nm Integration Time 0.5 -2 sec Centroiding Accuracy Limiting Magnitude > 21 guiding mode 20 χ 20 pixels 600 -700 nm 0.01 -2 sec 0.2 pixel wavefront sensing > 12.5 χ 12.5 mm 2 00 -600 nm; 700 -lOOOnm > 30 sec 0.1 pixel 16 (for 0.1 sec int time) 16, distributed over 400 points The CCD head (see Fig. 2 ) represents a compact mechanical design and is composed of the sealed box with a A/R coated glass window, the small or large CCD chip, the highly effective two stage Peltier cooler, two temperature sensors -one for the chip and the second for the box surface, hermetically sealed feed-through connectors, a liquid cooled heat exchanger, a external connector board with video preamplifier and cables to the array control electronic box. Furthermore the excellent performance of the CCD head is characterized by a minimum life time of 10 years, high positioning accuracy of the chip and high thermal stability to maintain the surface temperature of the head close (i.e., ±1°C) to ambient by using liquid cooling. The CCD sensors are front illuminated frame transfer devices with a "2.5-phase" Virtual Phase image section. In comparison to conventional front illuminated CDDs the virtual phase 375
doi:10.1007/978-94-011-0383-1_68 fatcat:uwqnorxbcnhzrnayyc2uubco5e