Vibration-insensitive interferometer for on-line measurements.

We have realized a digital Twyman-Green interferometer to measure the quality of optical surfaces in unstable environments. The system yields accurate measurements even in the presence of severe mechanical vibrations. The interferograms are decoded by application of a spatial-carrier phase-shifting fringe-analysis technique. The interferometer was mounted over a production machine and used for on-line measurements of aspheric mirror surfaces during the figuring and polishing process.