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Measuring Aspheric Lenses

Photonics.com
May 2009
ROCHESTER, NY, May 14, 2009 – In a discussion on aspheric lenses at Optifab 2009, Piotr Szwaykowski of Engineering Synthesis Design Inc. compared a newly developed single-measurement Fizeau interferometer with conventional interferometric stitching methods and mechanical stylus profiles to see how well each method measured aspheric surfaces.

The new interferometer is based on the Fizeau configuration and uses a sub-Nyquist CCD camera as a detector. The camera design allow the instrument to record very dense fringe patterns of up to 4 fringes/pixel, enabling processing of interferograms with hundreds of fringes in the field of view.

The tests showed good correlation and also highlighted the strengths and weaknesses of each method. “All of the measurements came with lateral scale,” Szwaykowski said.

As a result of the comparison, Szwaykowski and his colleagues came to the conclusion that the measurements of a set of aspheric lenses using the three interferometers generally produced the same results for all three instruments. An adjusted aperture kept the comparisons the same, he said.

The difference between the measurements can be accredited to the disparities in the measurement of the radius of curvatures coupled with the aspheric surfaces. “When you do the measurements with the different systems you start seeing a difference,” Szwaykowski said.

Amanda D. Francoeur
amanda.francoeur@laurin.com



GLOSSARY
interferometer
An instrument that employs the interference of lightwaves to measure the accuracy of optical surfaces; it can measure a length in terms of the length of a wave of light by using interference phenomena based on the wave characteristics of light. Interferometers are used extensively for testing optical elements during manufacture. Typical designs include the Michelson, Twyman-Green and Fizeau interferometers. The basic interferometer components are a light source, a beamsplitter, a reference...
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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