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SUMMARY:The OOF Holography Technique: Correcting the Effects of Gravity an
 d Thermal Gradients on Large Filled-Aperture Telescopes - Bojan Nikolic\, 
 Cavendish Astrophysics
DTSTART:20090428T153000Z
DTEND:20090428T163000Z
UID:TALK17803@talks.cam.ac.uk
CONTACT:Jane Buckle
DESCRIPTION:The maximum practical size of large single-dish telescopes is 
 mainly\ndefined by the effects three forces: gravity\, thermal gradients\,
  and\nwind. All of these can in principle be corrected by the new generati
 on\nof active surfaces on telescopes if we knew the actual deformations\nt
 hat are caused by them. At current cm\, mm and sub-mm telescopes\,\nmeasur
 ing these deformations corresponds to measurement of one part in\na millio
 n which is challenging for conventional survey techniques. In\nthis talk I
  will introduce the phase-retrieval holography technique\nbased on Out-Of-
 Focus (OOF) beam maps that is particularly suited to\nmeasuring these defo
 rmations. I will also present the application of\nthis technique to the 10
 0m-diameter Green Bank Telescope where we have\nbeen able to eliminate res
 idual gain variation due to gravity and open\nup the daytime for efficient
  observations at mm-wavelengths.
LOCATION:Ryle Seminar Room\, Cavendish Laboratory
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