A Measuring Interferometer for High Accuracy Alignment

An interferometer is described that is capable of measuring the deviation of a target device from a plane with an accuracy of 0.1 micro, when the interferometer-target separation is as much as 10 m. This interferometer resembles one described in 1965 by Baldwin and Whitten in that they both use a Kösters prism and a Porro prism. The present use of a laser for the light source yields nonlocalized fringes at the output that are easily monitored by an electronic fringe detector.