CALIBRATION OF A DIFFRACTIVE COMPENSATION OR ABSOLUTE NORMAL ELEMENT (TWIN OR DUAL CGH) BY MEANS OF WAVE FRONT ERRORS OF THE SPHERICAL AUXILIARY WAVE

摘要

The invention relates to a method for calibrating a diffractive compensation or absolute normal element for an interferometric absolute test of aspheric surfaces, wherein a complex coded computer-generated hologram (11, 12) is prepared as compensation or absolute normal element, said hologram reconstructing both an aspheric wave that is suitable for performing interferometric measurement of the aspheric surface (8) to be tested or a wave front and a spherical auxiliary wave, wherein interferometric measurement is carried out on the basis of the spherical auxiliary wave in order to determine wave front errors of the spherical auxiliary wave elicited by the computer-generated hologram (11, 12). The inventive method is characterized in that positioning errors of a writing beam is detected during the production of the computer-generated hologram (11, 12) on the basis of the wave front errors of the spherical auxiliary wave elicited by the computer-generated hologram and the probable wave front errors of the aspheric wave are calculated on the basis of the positioning errors and used for calibration. The inventive method makes it possible to achieve a complete interferometric absolute test of aspheric surfaces.