Method of mathematical compensation of deviation from flatness of reference optical elements in interference setups

This article examines the problem of reducing interferometer measurement errors for optical surface flatness deviations (measurement errors), a topical issue in the optical industry. It is shown that in order to reduce the error of measurement data, it is necessary to eliminate the component caused by deviations in the shape of the reference surfaces of the optical elements of Fizeau or Twyman-Green interferometers. Two main groups of methods for reducing the measurement error of deviations from flatness are briefly described: methods using a liquid standard and three-plane methods. A method has been developed for mathematical compensation of deviations from flatness of reference optical elements (attachments) in Fizeau-type interference installations. This method is based on the three-plane method with wavefront expansion in Zernike polynomials up to the fifth order and allows you to determine the topography of the reference surfaces of the nozzles. To implement the three- plane method, mathematical expressions are derived, by which the main parameters of the deviation of the shape of the reference surfaces are determined. The results of the practical implementation of the three-plane method using a measure of deviation from flatness with a diameter of 300 mm are presented. Experimental studies were carried out at the Research Institute of Optical and Electronic Instrumentation. The components of the instrumental measurement error are estimated. It was revealed that the greatest contribution to the measurement error is made by the random measurement error and the component caused by the deformation of the fl at plates used during their rotation. Application of the proposed mathematical compensation method made it possible to reduce the measurement error of parameters of deviation from flatness of optical surfaces at the enterprise by more than 30 %, its implementation and use can be useful at optical-mechanical enterprises for quality control of deviation of the shape of large-sized optical parts.

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