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Pseudo-Nulling Mach-Zehnder Metrology

Case ID:

UA19-213

Invention:

This technology is a novel Mach-Zehnder interferometer that uses a a pseudo-nulling configuration with a converging beam, to test two optical components against each other, rather that testing one optical component against a reference component

Background:

As the capability of optical manufacturing has grown such that it is easy to mass produce optical components with non-symmetric surfaces, optical metrology – the process of measuring these surfaces – has also been forced to push in new directions to characterize complex optical surfaces. Various techniques have been used to measure large and small optical elements, from measuring local surface slopes in deflectometry to wavefront differences in interferometry and height differences in profilometry. However, measurement of steep slopes on optical surfaces remains a challenge for all methods and one that hinders fast, accurate measurement.

Interferometers are commonly used to characterize optical surfaces. Interferometers compare wavefront properties from a surface being tested with wavefront properties from a reference source through an output called an interferogram. This image contains contrast fringes representing the combination of wavefronts that reveals differences between the test surface and reference beam. One way of measuring complex optical surfaces is to introduce a “null lens” into the interferometer that acts to correct for deviations in the test surface such that the final interogram is a null image with no fringes. However, creating a physical null lens or a virtual null lens through computer generated holograms is a time-consuming process and one that must be repeated for each new surface under test. Therefore, it is desirable to find other approaches that act like a null lens without actually requiring a null lens.

Applications: