19 August 2005 Retrace error evaluation on a figure-measuring interferometer
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A micro-refractive lens figure error measurement is performed at the confocal position with the interferometer in reflection mode. The wavefront in the interferometer reflecting from the test surface inherently has aberrations at some level, and reflection from an imperfect test surface further deviates the wavefront and adds to the interferometer aberrations. The interferometer aberration causes each ray of light to reflect off the test lens and back into the interferometer at a different angle. Consequently, the ray takes a different path back through the interferometer and therefore accumulates a different aberration. The result is a re-trace error which increases with the test lens surface curvature and becomes significant in the micro-optic range. The dependence of test part radius on micro-lens figure-error-measuring interferometer wavefront bias data was confirmed both experimentally and by software simulation. Results clearly indicate that the re-trace error increases with test lens surface curvature. The fact that re-trace errors depend on the radius of the test part implies that when calibrating the instrument even with a perfect artifact, the calibration is nominally valid only when measuring parts with the same approximate radius as the calibration artifact. A compact micro-interferometer useful for measuring several properties of micro-lenses including figure error, was developed to verify this phenomenon. The instrument has the capability of measuring micro-lenses with radii of curvature between 150 μm and 3 mm.
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Neil Gardner, Neil Gardner, Angela Davies, Angela Davies, } "Retrace error evaluation on a figure-measuring interferometer", Proc. SPIE 5869, Optical Manufacturing and Testing VI, 58690V (19 August 2005); doi: 10.1117/12.617549; https://doi.org/10.1117/12.617549

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