Flatness measurement using a grazing incidence interferometer

Abstract

The purpose of this work is to report results of flatness measurements using a grazing incidence interferometer. We show that this interferometer provides enough accuracy to measure nominally flat polishing tools and rough surfaces. In order to calculate the deformation of the surface under test, an interferogram is analyzed with digital imaging techniques based on Fourier methods. We found experimentally that the entire surface topography can be recovered with errors lower than $\sim 0.6 \mu $m, or $\sim \lambda_{eqv} / 6$, where $\lambda _{eqv} = 3.6441 \mu$m is the equivalent wavelength of the interferometer.