Research On Optical Interference Aspheric Measurement Using Axial Scanning

Rotationally symmetric aspheric optical elements have the advantages of correcting aberration,improving image quality and optimizing the optical structure.They have been widely used in various optical systems,but their freedom of shape brings great difficulties to the measurement.When measure the aspheric surface with scanning interference,the standard spherical wave with different radii radiated from the interferometer contact with the aspheric surface,and the circular interference fringes with sparse density are generated near the tangent point.According to this,the aspheric surface is divided into many sub-apertures,and the null position of each sub-aperture is connect to the vertex position by phase connection technique.In this paper the main research contents are:According to the design formula of aspherical surface,analyze the aspheric surface by the characteristic attribute.Research the influence factors of measuring the aspheric surface with scanning interference.Then plan scanning path of aspheric surface and define the range of each sub-aperture.Build Fizeau interference model,using ray tracing,fitting,reverse tracing and re-tracing to reduce the impact of distorting in the interference system.Calibrate the angle between the test ray and the optical axis,and obtain the optical difference between the reference path and test path.Move the aspheric surface on-axial to complete the phase shift and scanning process.Using a combination of large travel stage and ultra-precision stage to move the aspheric surface on the experiment.Design a four-dimensional adjustment frame to adjust the posture of the aspherical surface moving on axis.Obtain the interference wavefront,and remove the error of the adjustment.Extract the null position to reconstruct the aspheric surface by phase connection algorithm.The construction result is almost the same as the measurement of Taylor Hobson,and the RMS difference is about 1/30?(?=632.8nm).