Long gauge block measurements based on a Twyman-Green interferometer and three stabilized lasers

An interferometer is realized, based on the Twyman-Green Interferometer principle for the calibration of long gauge blocks and length bars in the 100-1000 mm range with an uncertainty of 0.02 micrometers + 0,1 micrometers /m. Also the expansion coefficient of gauge blocks and even of rod-shaped materials with non-optical flat faces can be calibrated in the 18-22 degrees C range with an uncertainty below 1 X 10-7/K. The set-up basically follows the most commonly used interferometer arrangements for long gauge blocks as they are described by Darnedde, Ikonen and Lewis where the most similarities with the latter occur. The set- up has some peculiarities which make the measurement straightforward, accurate and reliable