Measurement of Aspherical Form of Lens by Scanning Electron Microscope

Abstract

Although optical methods have been proposed for the profile measurement of aspherical lens, further research is needed to improve the accuracy of the machining. A method for the measurement of small diameter lenses was developed using a scanning electron microscope. Photo semiconductors were used to detect backscattered electrons which were reflected on the surface of the lens. A new simple algorithm which makes it possible to derive direction angle and slant angle of the normal at the respective observed points was proposed. The slope of a plastic aspherical lens was measured in terms of the normal of the profile. The results were illustrated as contour circles of equi slope. The difference between the neighboring radii of the circles for the slope varied at constant intervals and was not made equal due to the asphericity. A profile of the asphericity along the radial direction was obtained by integrating the slope.