Aspheric optical surface profiling based on laser scanning and auto-collimation

Abstract

Nowadays the utilization of aspheric lenses has become more and more popular, enabling highly increased degree of freedom for optical design and simultaneously improving the performance of optical systems. Fast and accurate surface profiling of these aspheric components is a real demand in characterization and optimization of the optical systems. In this paper, a novel and simple surface profiler instrument is designed and developed to fulfill the ever increasing need of testing axially symmetric aspheric surface. The proposed instrument is implemented based on a unique mapping between the position and rotation angle of reflective mirror in optical path and the coordinate of reflection point on the surface during rapid laser beam scanning. High accuracy of the proposed surface profiling method is ensured by high-resolution grating guide rail, indexing plate and position sensitive detector based on laser auto-collimation and beam center-fitting. Testing the meridian line of both a convex and a concave surfaces has been experimentally demonstrated using the developed instrument. In comparison to tested results from conventional image measuring instrument and coordinate measuring machine, coefficient of determination better than 0.99999 and RMS less than 1.5 µm have been achieved, which validates the feasibility of this method. Analysis on the systematic error is beneficial to further improve its measurement accuracy. The presented instrument-essentially builds on the geometrical optics technique-provides a powerful tool to measure the aspheric surfaces quickly and accurately with stable structure and simple algorithm.