<title>Five-order correction adaptive optics system for meter-class telescopes</title>

Abstract

An adaptive optics system for small to medium astronomical telescopes has been designed and is under construction. This adaptive optics system corrects the five lowest order Zernike wavefront aberrations, providing near diffiaction-limited performance for telescope diameters smaller than about 5*r0, and useful correction up to about 10*r0. This adaptive optics system design consists of a lens-based wavefront aberrator, a CCD-based Shack-Hartmann wavefront sensor, and a personal computer-based feedback loop.The wavefront aberrator uses a series ofvoice-coil translated thin lenses in a collimated beam to compensate tip, tilt, defocus, xy-astigmatism, and x2-y2-astigmatism. Translating weak lenses perpendicular to the optical axis applies the tip and tilt corrections. Defocus and astigmatism are applied by translating along the optical axis, one lens of a nearly zero-power lens pair. Voice coil actuators reduce cost and permit relatively large lens translations.The wavefront sensor uses a single lens to focus four subapertures. Weak beamsteering prisms align the images near the readout edge of a small CCD. Personal computer software rapidly converts the quad sensor signals to the voltages for the wavefront aberrator voice coils.Internal optics include an alignment pinhole to aid realignment. Calibration, including determining the measurement matrix and the reconstructor, will be automated.