Polarization-Fizeau interferometer enabling phase measurement with reduced uncertainty

G. Fütterer

doi:10.1117/12.2272001

15 June 2017 Polarization-Fizeau interferometer enabling phase measurement with reduced uncertainty

G. Fütterer

Proceedings Volume 10326, Fourth European Seminar on Precision Optics Manufacturing; 103260B (2017) https://doi.org/10.1117/12.2272001
Event: Fourth European Seminar on Precision Optics Manufacturing, 2017, Teisnach, Germany

Abstract

A Fizeau interferometer is significantly less sensitive to vibrations and air turbulence than other types of interferometers. This is due to the common path of the reference wave front and the object wave front. A common path arrangement offers the opportunity to reduce systematic errors of the measured phase of the surface under test (SUT). That is why Fizeau type interferometers are most commonly used to test e.g. plane surfaces, spheres or aspheres. A reduced uncertainty of the measured phase distribution can be obtained if the reference surface is placed close to the SUT. Multiple beam reflections will produce interference fringes, which are not sinusoidal. Furthermore, the discrete intensity distribution depends on the reflectance of the reference surface and the reflectance of the SUT. Some surfaces to be tested show significant variations of the local reflectance, e.g. lithographic masks with 0.05 ≤ r(x,y) ≤ 0.95. Thus, the inherent potential of phase shifting algorithms cannot be used.

A modification of the reference surface can be applied. An on-axis polarization beam splitter, which is placed in the plane of the reference surface, separates the two surfaces, which are imaged onto the detector. Thus, true two beam interference can be obtained. The potential of phase shifting algorithms can be used. The interference contrast is high, even if large local variations of r(x,y) are present. In addition, high speed operation is enabled. The embodiment of a modified Fizeau type interferometer will be described.

Citation Download Citation

G. Fütterer "Polarization-Fizeau interferometer enabling phase measurement with reduced uncertainty", Proc. SPIE 10326, Fourth European Seminar on Precision Optics Manufacturing, 103260B (15 June 2017); https://doi.org/10.1117/12.2272001

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