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11 August 2008 Measurements of aspheric surfaces
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A newly developed interferometer for characterization of aspheric surfaces is presented. The interferometer is based on the Fizeau configuration and uses a sub-Nyquist CCD camera as a detector. Due to the camera design, the instrument is capable of recording very dense fringe patterns of up to 4 fringes/pixel. This enables processing of interferograms with hundreds of fringes in the field of view. Thus, the interferometer can be used to measure many types of aspheric surfaces using a standard transmission sphere as a reference. However, the main obstacle associated with this kind of interferometer is caused by the presence of so called "re-trace" errors, which can be significant. Such errors occur from un-equal optical paths the reference and test beams travel through in the optical system of the interferometer. A ray tracing procedure has been developed to subtract the influence of the optical system of the interferometer on the measurement. This method of error compensation results in reducing measurement errors to λ/5 PV (peak to valley) for the full range of fringe densities with the low order aberrations not exceeding λ/10. We present measurements of test surfaces illustrating the effectiveness of the error compensation procedures as well as preliminary measurements of multiple aspheric surfaces.
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Piotr Szwaykowski and Raymond Castonguay "Measurements of aspheric surfaces", Proc. SPIE 7063, Interferometry XIV: Techniques and Analysis, 706317 (11 August 2008);

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