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14 August 2006 Absolute interferometry for surface shapes with large steps by wavelength tuning with a mechanical phase shift
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Abstract
Profiling of optical surfaces with discontinuous steps by monochromatic interferometry has the ambiguity of multiples of a quarter wavelength. Wavelength-tuning interferometry can measure these surfaces with a unit of synthetic wavelength that is usually much larger than that of the original source. In order to solve this problem, the fractional phases of the interferograms before and after wavelength tuning should be carefully estimated. Phase-shifting interferometry with a mechanical phase shift by a PZT transducer determines the fractional phases of the interferograms with a resolution of better than one part in 250 of the wavelength. After subtracting the mechanical drift of the test surface during wavelength tuning, the absolute distance between the test surface and the reference surface is measured with an uncertainty better than a quarter wavelength. An optical flat with two gauge blocks 1 mm in height contacting the surface is measured by a Fizeau interferometer. Experimental results demonstrate that the surface profile can finally be measured with an accuracy of 20 nm.
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Kenichi Hibino, Yosuke Tani, Toshiyuki Takatsuji, Youichi Bitou, Shinichi Warisawa, and Mamoru Mitsuishi "Absolute interferometry for surface shapes with large steps by wavelength tuning with a mechanical phase shift", Proc. SPIE 6292, Interferometry XIII: Techniques and Analysis, 62920Q (14 August 2006); https://doi.org/10.1117/12.679314
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