Scanning phase shift interferometry in length measurement

Abstract

The Ultra-Precision Interferometer of PTB has been equipped with an external measuring path which can be cooled down to 10 K by a pulse tube cooler. Due to the cooling measures vibration is provoked in the interferometer system. Moreover, since the cooled part of the interferometer is a separate extension to the stabilized vacuum chamber, temperature changes can lead to a drift of the length of the beam path. Most phase stepping algorithms in length measurements by interferometry require fixed and well-known phase steps between the recorded interferograms. Hence, in the presence of unstable conditions in the environment of the experiment phase shifting interferometry cannot be performed as usual. Therefore, we have adapted the so-called scanning phase shift technique for the application in interferometric length measurements.