Profile Measurement of a Steep Aspheric Surface Using a Laser Beam

Abstract

Two noncontact methods for measuring a surface profile of a steep aspheric surface, which are called Type 1 and Type 2, are presented. The scheme is based on a direct measurement of a slope of a surface by using a surface reflected laser beam. For the Type 1, a surface under test is moved by means of a rotary position table and a linear position table so that a returning laser beam is detected by a centering photodetector. For the Type 2, a laser beam is scanned by means of a galvanometer mirror instead of linear movement of a surface under test by means of a linear position table in the Type 1. A surface profile is determined by using a simple curve fitting technique for the measured data. Accuracy of the method is evaluated by an analysis of error caused by a misalignment of an optical setup. Usefulness of the proposed methods is shown throught experimental tests of a surface profile measurement of steep aspheric lenses.