16 October 2017 Tailored complex degree of mutual coherence for plane-of-interest interferometry with reduced measurement uncertainty
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Proceedings Volume 10448, Optifab 2017; 104481I (2017) https://doi.org/10.1117/12.2279834
Event: SPIE Optifab, 2017, Rochester, New York, United States
Abstract
A problem of interferometers is the elimination of parasitic reflections. Parasitic reflections and modulated intensity signals, which are not related to the reference surface (REF) or the surface under test (SUT) in a direct way, can increase the measurement uncertainty significantly. In some situations standard methods might be used in order to eliminate reflections from the backside of the optical element under test. For instance, match the test object to an absorber, while taking the complex refractive index into account, can cancel out back reflections completely. This causes additional setup time and chemical contamination.

In some situations an angular offset might be combined with an aperture stop. This reduces spatial resolution and it does not work if the disturbing wave field propagates in the same direction as the wave field, which propagates from the SUT. However, a stack of surfaces is a problem.

An increased spectral bandwidth might be used in order to obtain a separation of the plane-of-interest from other planes. Depending on the interferometer used, this might require an optical path difference of zero or it might cause a reduction of the visibility to V < 0.5.

Contrary to these methods, a tailored complex degree of mutual coherence can be used. High visibility is obtained for a single plane-of-interest. Wave fields of interest are shifted against each other. The reduction of the measurement uncertainty, as well as the embodiment of a modified interferometer, will be discussed.
© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
G. Fütterer, "Tailored complex degree of mutual coherence for plane-of-interest interferometry with reduced measurement uncertainty", Proc. SPIE 10448, Optifab 2017, 104481I (16 October 2017); doi: 10.1117/12.2279834; https://doi.org/10.1117/12.2279834
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