Method of measuring a shape of an optical surface based on computationally combined surface region measurements and interferometric measuring device

Abstract

Measuring a shape of an optical surface ( 14 ) of a test object ( 12 ) includes: providing an interferometric measuring device ( 16 ) generating a measurement wave ( 18 ); arranging the measuring device ( 16 ) and the test object ( 12 ) consecutively at different measurement positions relative to each other, such that different regions ( 20 ) of the optical surface ( 14 ) are illuminated by the measurement wave ( 18 ); measuring positional coordinates of the measuring device ( 16 ) at the different measurement positions in relation to the test object ( 12 ); obtaining surface region measurements by interferometrically measuring the wavefront of the measurement wave ( 18 ) after interaction with the respective region ( 20 ) of the optical surface ( 14 ) using the measuring device ( 16 ) in each of the measurement positions; and determining the actual shape of the optical surface ( 14 ) by computationally combining the sub-surface measurements based on the measured positional coordinates of the measuring device ( 16 ) at each of the measurement positions.

1 . An optical element having an optical surface, which optical surface is adapted to a non-spherical target shape, such that variations of the actual shape of the optical surface with respect to the target shape having a spatial wavelength between 0.015 mm and 2 mm are limited to at most 100 pm RMS. 
     
     
         2 . The optical element according to  claim 1 ,
 wherein the optical surface is adapted to the non-spherical target shape, such that variations of the actual shape of the optical surface with respect to the target shape having a spatial wavelength between 0.015 mm and 30 mm are limited to at most 100 pm RMS.   
     
     
         3 . The optical element according to  claim 1 ,
 wherein the target shape of the optical surface is a free form surface having no rotational symmetry and the target shape has a deviation from a best fitting spherical surface for the free form surface of at least 5 μm.   
     
     
         4 . The optical element according to  claim 1 ,
 wherein the target shape of the optical surface is a rotationally symmetric aspherical surface and the target shape has a deviation from a best fitting spherical surface for the aspherical surface of at least 500 μm.   
     
     
         5 . An interferometric measuring device configured for measuring a shape of an optical surface of a test object, comprising:
 a detection apparatus configured to record an interferogram, and   imaging optics comprising at least one curved mirror and configured to image the optical surface onto the detection apparatus.   
     
     
         6 . The interferometric measuring device according to  claim 5 ,
 wherein the imaging optics comprise two wavefront forming surfaces, which are configured such that the optical path utilized for imaging the optical surface onto the detection apparatus comprises a focus point located between the two wavefront forming surfaces.   
     
     
         7 . The interferometric measuring device according to  claim 5 ,
 wherein the imaging optics comprise at least one parabolic mirror.   
     
     
         8 . The interferometric measuring device according to  claim 5 ,
 wherein the imaging optics are configured such that the optical path utilized for imaging the optical surface onto the detection apparatus strikes the curved mirror twice.