Authors: Nikolay Voznesenskiy, Mariia Voznesenskaia, Natalia Petrova, Artur Abels

Paper Abstract

Interferometric inspection of optical surfaces and wavefronts requires permanently increasing accuracy. Therefore interferometric equipment is being improved and improved continuously. Point-diffraction interferometers (PDI) with an “inbuilt” reference wavefront originating from light diffraction by a pinhole aperture are potentially capable to produce the highest possible accuracy of a surface figure or wavefront characterization.

The most mentioned configurations and their versions like Linnik-Smart and Sommargren schemes produce low-contrast spare-striped fringe patterns instead of full-contrast distinct interferograms, like e.g. produced by Fizeau interferometers, with clear phase shifting (PS) data flow. 

The concept of a PDI presented in this paper is to provide two perpendicularly outgoing wavefronts – test and reference ones – with mutual intensity regulation and arbitrary and stable phase shifts of one wavefront relative to the other. Such concept is also targeted to provide user-friendly measuring conditions similarly to interferometers which are in common use. 

Advantages of such arrangement of the PDI are: high numerical aperture (NA = 0.55), clear fringe patterns of high contrast, high accuracy of surface figure testing with wave-front RMS error 0.125 nm and wave-front RMS repeatability 0.05 nm. Performance of the PDI is illustrated by tables of repeatability and test surface profile plots for different azimuthal angles.

Paper Details

Date Published: 13 May 2013
PDF: 13 pages
Proc. SPIE 8788, Optical Measurement Systems for Industrial Inspection VIII, 878805 (13 May 2013); doi: 10.1117/12.2020618

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