Closed-loop aberration correction by use of a modal Zernike wave-front sensor

We describe the practical implementation of a closed-loop adaptive-optics s ystem incorporating a novel modal wave-front sensor. The sensor consists of a static binary-phase computer-generated holographic element, which genera tes a pattern of spots in a detector plane. Intensity differences between s ymmetric pairs of these spots give a direct measure of the Zernike mode amp litudes that are present in the input wave front. We use a ferroelectric li quid-crystal spatial light modulator in conjunction with a 4-f system and a spatial filter as a wave-front correction element. We present results show ing a rapid increase in Strehl ratio and focal spot quality as the system c orrects for deliberately introduced aberrations. (C) 2000 Optical Society o f America OCIS codes: 090.1000, 110.7350.