Designer detectors: a new paradigm for instrument development

The designs of optical and infrared detectors are limited to rectangular arrays of square pixels, aren't they? Not any more! This paper presents a new design paradigm -- custom designed pixel morphology -- that provides significantly better performance in cases where a low light level signal must be detected over a non-rectangular area. Two examples of this new approach are presented in this paper. Both examples are CCDs used for adaptive optics (AO) wavefront sensing: (1) a CCD optimized for curvature wavefront sensing and, (2) a CCD designed for eliminating the laser spot elongation problem that plagues laser guide star AO. In both cases, the detectors will achieve photon-noise limited performance, the Holy Grail for any detector. The name proposed for the customized pixel morphology is "taxel," for "time area element," and a CCD with specialized taxel design is called a "designer detector." The curvature AO CCD was designed and fabricated by MIT Lincoln Laboratory, and fully tested by ESO. This CCD will be used by the Canada-France-Hawaii Telescope to upgrade their AO system from 19 to 105 subapertures. The laser guide star CCD, which was recently funded by a $1.1M grant from the National Science Foundation, will be demonstrated in the LGS system of an 8 - 10 meter telescope, paving the way for a larger chip for the Extremely Large Telescopes.