Wave front sensing for metrology by using optical filter

G. Fütterer

doi:10.1117/12.2530013

28 June 2019 Wave front sensing for metrology by using optical filter

G. Fütterer

Author Affiliations +

Proceedings Volume 11171, Sixth European Seminar on Precision Optics Manufacturing; 111710K (2019) https://doi.org/10.1117/12.2530013
Event: Sixth European Seminar on Precision Optics Manufacturing, 2019, Teisnach, Germany

Abstract

An interferometric problem is the limited fringe density, which is due to the limited allowed slope difference of superimposed wave fronts. Thus, the angular dynamic range of measurable surfaces and objects under test is limited. In other words, all shapes that deviate from a plane surface or a sphere represent a measuring problem in interferometers, or require an individually adapted null optics, which might cost e.g. 10 k∈ or more. In addition, ground surfaces cannot be measured in standard interferometers, except by using Speckle interferometry, which is limited in resolution. Freeform optics are very problematic. Even when polished, only tactile or confocal coordinate measurement might work. Several interferometers address the problem of the angular deviation to a sphere. For instance, lateral stitching on a curved surface, which is equivalent to the best-fit sphere, or longitudinal stitching is used. To use a tilted wave interferometer for asphere metrology is another option, which provides versatile measurement configurations. The approach discussed here is to use optical filters. The development of this technique is part of a project most recently started at the Technology Campus in Teisnach. The surface under test (SUT) is imaged onto an optical filter, which has a calibrated angular selectivity. Thus, the angles of the local wave front normal vectors are transferred into an intensity distribution. A set of angular measurements enables reduced uncertainty of the wave front measurement. Aspects as e.g. the working principle, boundary conditions and the identification of practical filters are discussed in the paper.

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G. Fütterer "Wave front sensing for metrology by using optical filter", Proc. SPIE 11171, Sixth European Seminar on Precision Optics Manufacturing, 111710K (28 June 2019); https://doi.org/10.1117/12.2530013

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KEYWORDS

Wavefronts

Aspheric lenses

Interferometers

Calibration

Spherical lenses

Optical filters

Optical spheres

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