Some aspects of error influences in interferometric measurements of optical surface forms

Interferometry is often used to measure the form of optical surfaces. While interferometry is generally expected to give high accuracy results, a variety of error influences exist which have to be considered. Some typical error influences which are often underestimated will be discussed in this paper. In flatness metrology, the main error influences are imperfections of the reference surfaces, specimen support or cavity influences. For non-flat surfaces like aspheres or free form surfaces, in particular the influence of errors from the determination of the lateral coordinates becomes very important. Sub-aperture interferometry copes with stitching errors, which can be reduced by Traceable Multi Sensor subaperture methods where the influence of the imaging system of the interferometer may dominate the error budget. This can be similar for other types of interferometers.