Beside lot of geometrical and functional parameters the surface shape is one of the most important values to be determined especially in finishing process of production. The shape determines the light refraction respectively reflection and thus influences directly the performance of the optics.
The shape accuracy can be easily measured interferometerically. Interferometry is an optical relative measuring principle which determines the deviation of a test sample from a reference. It is a very accurate measurement method allowing to detect aberrations in the range of parts of the measurement wavelength.
Commonly interferometers are used for testing spherical or flat surfaces. Other surface shapes like cylinders, toric, aspheres require special beam shaping optics to be testable.
Due to the fact that an interferometer only compares wavefronts with each other it can also be used to measure the wavefront quality of objectives in transmission.
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