Abstract

The Shack-Hartmann wavefront sensor is a miniaturized version of the classical Hartmann mask extended by using a two-dimensional array of lenslets that is optically conjugate to the wavefront surface under test. The sensitivity and dynamic range of the wavefront measurement is controlled by the combination of reimaging optics and the diameter and focal length of the lenslet array. This allows an adjustment of the gradient measurement sensitivity . As the beam size is reduced in reimaging the test surface, the angular spread of the beam is magnified. This magnification increases the size of the gradients or tilts of the ray bundles from micro-radians to milliradians for typical testing configurations. Measurements of such large angles are not so prone to error due to mechanical and thermal instabilities in the sensor equipment as are interferometric sensors where dimensional stability must always be measured in parts of a micron. It is this flexibility that makes it possible for the same sensor system to measure with very high accuracy the wavefront produced by a Hubble Space Telescope simulator and, with a change of lens array, the shape of f/0.7 paraboloids.

© 1997 Optical Society of America