Hartmann method for monitoring the shape of convex aspheric mirrors of large optical telescopes

Abstract

This paper discusses the possibility of using the Hartmann method to monitor the shape of convex aspheric mirrors of telescopes under manufacturing conditions. A Hartmann stop in the form of regular small-diameter apertures in an opaque screen is placed outside the mirror to be monitored and is illuminated by a pencil of parallel rays directed perpendicular to the mirror's symmetry axis. The role of recording device can be played by a linear array of CCDs or a photographic plate on whose sensitive surface a so-called Hartmann pattern is recorded. Subsequent mathematical processing makes it possible to determine the shape errors of the meridional cross section. To provide monitoring of the entire surface, the latter is rotated around the symmetry axis by any given angle any number of times, and this makes it possible to completely automate the monitoring process of both ground and polished surfaces under manufacturing conditions.