Researches On Profile Extraction Algorithm Of Harmonic Diffractive Elements Based On Confocal Scanning

With the improvement of the performance of modern optical system, it hasbecome one of research hot spot that developing diffractive optical element withcomplex structure. The basement of traditional diffraction optical element is planaror spherical. It can correct the spherical aberration and reduce the number of opticalelements by introducing aspheric optical elements. The aspheric surface has becomethe basement of some diffraction optical elements with high surface figure inultra-precision optical engineering. It is a great challenge for the surfacemeasurement of modern optical elements.The subject “researches on profile extraction algorithm of harmonic diffractiveelements based on confocal scanning” propose the solution of profile measuring andprofile fitting algorithm specific to harmonic diffractive elements with asphericbasement. The main content of the subject including:Firstly, propose the solution of profile measuring according to analysis of theharmonic diffractive elements with aspheric basement. The process of scanning iscomposed of base-profile scanning and step-profile scanning. Base-profile scanningis aimed at the measurement of the aspheric base, while step-profile scanning isaimed at the measurement of the step microstructure.Secondly, carry out the research of Gauss filter and fitting method. It needs tochoose different step length to different scanning areal. Choose Levenberg-Marquardt algorithm for the profile fitting of zero-order diffraction plane.Thirdly, analyze the error caused by the coordinate system. The error includeseccentricity error and tilt error. To make correction with the eccentricity error, wecan let the bottom center coincide with the start point of measuring; To makecorrection with the tilt error,we can average the points that symmetric with thecenter aixFinally, carry out relevant experimental. Carry on the experimental of axialcharacteristic response and repeatability for measuring one point. Carry on theexperimental that verify the capability for measuring curve surface. Carry on theexperimental of the profile measuring for harmonic diffractive elements, finish themeasuring of profile parameters and surface residual.