Abstract
We are developing a form measurement system for the surfaces of freeform optics and large conventional optics. The specifications of the optics are diameters up to 1.5 m and radii of curvature down to 10 m. This includes optics like telescope mirror segments and synchrotron optics. Using a Fizeau interferometer, we propose a subaperture stitching method that involves vertically aligning the interferometer’s optical axis to the local surface gradient and measuring the absolute distance from the interferometer’s reference flat to the specimen. Experimental results for the absolute distance measurement are shown.
Highlights
Measuring the form of an optical surface with a Fizeau interferometer with an aperture smaller than the specimen’s diameter makes it necessary to use subaperture stitching [1]
By measuring the topography of each subaperture and the distance from the interferometer’s reference flat to the specimen, we will position the topographies from the subaperture measurements in a global coordinate system before stitching
Our measurement setup [4] will consist of a Fizeau interferometer with a flat reference surface and a specimen, which are mounted on a motion system
Summary
Measuring the form of an optical surface with a Fizeau interferometer with an aperture smaller than the specimen’s diameter makes it necessary to use subaperture stitching [1]. By measuring the topography of each subaperture and the distance from the interferometer’s reference flat to the specimen, we will position the topographies from the subaperture measurements in a global coordinate system before stitching. In this way, the stitching process becomes a linearized problem without the need for lateral image registration or computationally intensive multidimensional stitching
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