Why can we only phase the Keck telescope segments to 30 nanometers (3x worse than the TMT requirement)?

Gary Chanan
University of California, Irvine
Tuesday, April 11, 2017
4:00 pm
NS2 1201


In order for a segmented-mirror telescope like Keck to achieve its full diffraction limit, the telescope must be phased; that is, the steps between segments must be reduced to a small fraction of ​the​ wavelength​ of light​. Exactly how well things need to be phased depends upon on a number of factors​; b​ecause ​Keck image quality is limited by segment figure errors and other effects (to be discussed), ​phasing the telescope to ​30 nm has proved adequate. The problem is that the phasing requirement for the Thirty Meter Telescope (TMT) is 10 nm, and for many years we have not understood why we cannot d​o better at​ Keck. A recent investigation into the Keck phasing problems has revealed some subtle and unexpected optical effects, which have important implications for ​TMT and for ​large segmented-mirror telescopes in general.


Michael Cooper