A new algorithm for the absolute metrology of optical surfaces

Mitchell, John Benjamin (1996) A new algorithm for the absolute metrology of optical surfaces. (PhD thesis), Kingston University, uk.bl.ethos.554989.


In this thesis, the problem of the metrology of optical surfaces is examined. The need for accurate metrology is established with regard to optical wavefronts reflecting or refracting at the surfaces of optical components. Optical interferometry is identified as the most useful analytical tool for surface metrology by virtue of its high precision and accuracy. Accordingly the theory of interferometry is briefly presented. The application of the theory to the interferometric instruments is shown together with measuring configurations for the various optical surfaces commonly encountered. An extensive overview of the techniques used to evaluate data from interferometric measurements is given with particular emphasis on precision phase measuring methods. Most interferometric measurements of surfaces aremade relative to a reference surface of high quality. Where the accuracy of the surface to be measured is comparable to, or better than, that of the reference surface, an absolute measurement technique is required in order to give meaningful results. A review is given of the existing methods for the absolute measurement of nominally flat and spherical surfaces and the shortcomings of these methods. A new algorithm for the absolute testing of flat surfaces is developed, based on relative measurements of pairs from a population of three test flats in a number of positional combinations. The new method has a number of potential advantages over those previously described, particularly since it yields information about the flats over their entire surfaces on a square grid of points. The implementation of the new method on a Zygo Mark IV interferometer is described together with experimental results using both synthesized and actualexperimental data. Suggestions for improvements to the method and its implementation are made. A speculative study of other possible techniques for absolute flatness measurement is presented, including the possible application of the Ritchey-Common test, point diffraction interferometry, phase conjugation and profilometry. A full and up to date survey of the pertinent literature is given throughout the thesis. "Mister Logic" Viz Comic 72 June/July 1995 "We must, therefore, recognise that what is designated by the terms "glance", "hand", and, in general, "body" is a system of systems devoted to the inspection of a world and capable of leaping over distances, piercing the perceptual future, and outlining hollows and reliefs, distances and deviations- a meaning in the inconceivable flatness of being". Maurice Merleau-Ponty, "Indirect language and the voices of silence" . "THE VERY BIG STUPID is a thing which breeds by eating The Future. Have you seen it? It sometimes disguises itself as a good-looking quarterly bottom line, derived by closing the R&D Department". Frank Zappa, "The Real Frank Zappa Book". "Heavens!" said Mrs Lambchop. "Gosh!" said Arthur. "Stanley's flat!" "As a pancake," said Mr Lambchop. "Darndest thing I've ever seen." "Let's all have breakfast," Mrs Lambchop said. "Then Stanley and I will go and see Doctor Dan and hear what he has to say. " Jeff Brown, "Flat Stanley".

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