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An Off-Axis Mirror for the Quest Spectrograph


R.F. Royce - POC was selected to fabricate an off-axis mirror for the Quest project, a multi-national collaboration of astronomers and physicists, searching for dark matter via the gravitational lensing of quasars. The observations will utilize the 3.5 meter WIYN Telescope, the newest and second largest telescope on Kitt Peak. Quest scientists have designed and fabricated a dual red and blue light spectrograph intended to separately image spectra from closely separated or lensed objects. 


This spectrograph, pictured above, will be attached to the bottom of the WIYN telescope at the Cassegrain focus. Space restrictions between the observatory floor and the end of the telescope required the spectrographic apparatus be  contained within about 30 inches. This resulted in the need for a high wavefront but fairly fast off-axis mirror. We successfully fabricated a 3 inch diameter 19.5 inch focal length (f/6.5) mirror having an off-axis displacement of 3.5 inches (2 inches off the side of the mirror). The mirror is the first element in the spectrograph's optical train and collimates light from the slit at the Cassegrain focus, passing it through a dichroic transmission grating that disperses the light and also separates it into blue and red end components that can be separately analyzed through individual (red and blue) optical systems and cameras by merely adjusting the angle of the grating. 

The WIYN Observatory is owned and operated by the WIYN Consortium, which consists of the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatories (NOAO). For more information about WIYN go to http://www.noao.edu/wiyn/wiyn.html