A cancellation technique for the validation of the reference profile of an interferometer

There are a number of methods by which to measure the surface flatness profile using an interferometer. These methods involve obtaining a fringe image that displays the surface profile by the interference between a reflected beam from the measured surface and a reflected beam from a reference surface. Since the reference functions as a datum, the accuracy of the measured results depends on the accuracy of the reference. The authors previously proposed a differential laser auto-collimation method with zero-point compensation for canceling the parabolic error caused by the systematic error of the measurement system. The extension of the differential laser auto-collimation with zero-point compensation is a cancellation technique for the validation of the reference for the interferometer. This measurement method consists of two steps. First, the measured surface is not irradiated by the laser beam, and the systematic error is obtained. Next, the measured surface is irradiated, and the surface profile that includes the systematic error is obtained. Finally, the surface profile is estimated using the difference between these two steps. In this article, the principle and the experimental results are shown.