A REFLECTIVE SHACK-HARTMANN WAVE-FRONT SENSOR FOR ADAPTIVE OPTICS

We describe a new wave-front sensor based on the efficient Shack-Hartm ann quad cell system. The key improvement to existing designs is a mod ified lenslet array. The traditional refractive lenslet array is repla ced with a segmented reflective system that allows individual control of each subaperture. This system has produced diffraction-limited slop e correction of the six 1.83-m mirrors of the MMT using a 9.9V magnitu de guide star and significant image improvement on guide stars as fain t as 11.3V magnitude, limited by the readout noise of the CCD quad cel l detector. Recent experiments with an improved detector indicate diff raction-limited imaging on guide stars as faint as the 15th magnitude. This optimized wave-front sensor, equally applicable to filled-apertu re telescopes, promises to extend the amount of sky coverage available for adaptive correction in the near IR.