Surface Metrology using One-element Interferometry

Abstract

Surface metrology is the key to make and retain high quality surfaces. There are many coordinate measurement methods and machines to measure large 3D surfaces. Some methods are: triangulation, time-of-flight, structured-lighting, photogrammetry and radio-holography. They differ in ease-of-use, economy, complexity and accuracy. Some, e.g. photogrammetry, measure point-by-point while others, e.g. holography, measure a point-cloud at one go. Some are spot-measurements while others are areal averages. Both photogrammetry and radio-holography are used to measure the surfaces of astronomical telescopes. Both phase-referenced and phase-recovered holographic techniques are used. In this paper we present yet another method to measure surfaces of large astronomical telescopes.