ESO Active Optics System: Verification On A Lm Diameter Test Mirror

Active optics, as envisaged for the ESO NTT, is based on four principles: 1. The linear relationship between the applied support force and the deformation of the mirror resting on a force based support system. 2. The orthogonality of the corrected aberrations. 3. The restriction to correct only those aberrations for which small forces are necessary, i.e. long wavelength aberrations as e.g. astigmatism and spherical aberration, which are also those modes induced by errors in the system. 4. The use of precalibrated forces for these corrections. Using the Shack-Hartmann test method for the analysis of the wavefront, we have confirmed these principles in an experiment with a lm diameter spherical mirror with a thickness of 18,9 mm and 78 supports.