On the absolute calibration of Shack-Hartmann sensors and UV laboratory wavefront measurements

Abstract

We experimentally investigate the practical range, sensitivity and precision of laboratory Shack-Hartmann wavefront measurements for aspheric mirrors and laser beams. Spot diagrams recorded on photographic film or photoresist-coated glass substrates are measured within 2 mu m reading steps for x and y coordinates. Special attention is paid to the absolute calibration of these measurements, e.g. to the geometric properties of the microlens arrays involved. A comparison is made between interferometric and Shack-Hartmann measurements for the same aberrating wavefront. Typical actual RMS residuals in angular transverse aberrations are of the order of 0.5" per sampling point when dividing a 12 cm diameter pupil in 5 mm X and Y steps. We argue that the recorded Shack-Hartmann spot arrays have a better intrinsic precision.