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CryoCam Back from the Dead (1Mar93) (from KPNO, NOAO Newsletter No. 33, 1 March 1993) We have replaced the TI 800 x 800 chip in the Cryogenic Camera with a new, thinned Ford 800 x 1200 CCD. Testing has just begun, but the instrument should be available for the spring 1993 semester and subsequently. In many ways the new chip is a great improvement over the old one. Most importantly it is flat, so the focus variations that plagued efforts to do accurate sky subtraction should be eliminated. Also, the thinning and backside treatment, applied by Dr. Michael Lesser of Steward Observatory, allow the chip to hold its UV flood for a long period of time even while it is warm. Thus, it can be flooded before the camera is sealed. We believe that one of the principal reasons for the low efficiency of the old system was the difficulty in UV flooding the CCD. The chip has 1200 15 um pixels in the spectral direction; the focus softens somewhat in the first and last 100 pixels. The chip has 9 electrons readout noise and three bright columns. No traps are apparent. The CryoCam was used on the 4-m telescope on the nights of 19-24 January 1993. Listed below are the chip quantum efficiency and a conservative estimate of the system efficiency measured with Grism 650 under less than perfect conditions. The system is relatively inefficient below 4000 A both because of the spectrograph optics and the CCD quantum efficiency curve which was optimized for the red to reduce fringing. Wavelength CCD QESystem Efficiency 4000 A 25% 4.2% 4500 A 51% 10.1% 5000 A 72% 13.2% 5500 A 77% 16.4% 6000 A 83% 14.9% 6500 A 86% 11.3% 7000 A 84% 7500 A 80% 8000 A 72% 8500 A 61% 9000 A 45% 9500 A 24% Todd Boroson, Rich Reed, David Vaughnn, Bill Ditsler
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