AAS 205th Meeting, 9-13 January 2005
Session 48 Visible-Light Telescopes, Instruments, and Technology
Poster, Tuesday, January 11, 2005, 9:20am-6:30pm, Exhibit Hall

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[48.10] A noiseless, kHz frame rate imaging detector for AO wavefront sensors based on MCPs read out with the Medipix2 CMOS pixel chip

J.V. Vallerga, J. B. McPhate, A.S. Tremsin, O.H.W. Siegmund (U.C. Berkeley), B. Mikulec, A.G. Clark (U. Geneva)

Future wavefront sensors in adaptive optics (AO) systems for the next generation of large telescopes (> 30 m diameter) will require large formats (512x512) , kHz frame rates, low readout noise (<3 electrons) and high optical QE. The current generation of CCDs cannot achieve the first three of these specifications simultaneously. We present a detector scheme that can meet the first three requirements with an optical QE > 40%. This detector consists of a vacuum tube with a proximity focused GaAs photocathode whose photoelectrons are amplified by microchannel plates and the resulting output charge cloud counted by a pixelated CMOS application specific integrated circuit (ASIC) called the Medipix2 (http://medipix.web.cern.ch/MEDIPIX/). Each 55 micron square pixel of the Medipix2 chip has an amplifier, discriminator and 14 bit counter and the 256x256 array can be read out in 287 microseconds. The chip is 3 side abuttable so a 512x512 array is feasible in one vacuum tube. We will present the first results with an open-faced, demountable version of the detector where we have mounted a pair of MCPs 500 microns above a Medipix2 readout inside a vacuum chamber and illuminated it with UV light. The results include: flat field response, spatial resolution, spatial linearity on the sub-pixel level and global event counting rate. We will also discuss the vacuum tube design and the fabrication issues associated with the Medipix2 surviving the tube making process.

If you would like more information about this abstract, please follow the link to http://www.ssl.berkeley.edu/\~mcphate/AO/ao_medipix.html. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract: jvv@ssl.berkeley.edu

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