Laser-Doppler-Distance-Sensor using phase evaluation for position, shape andvibration measurements

In this article we present a novel optical sensor allowing simultaneous measurements of axial position and tangential velocity of moving solid state objects. An extended laser Doppler velocimeter setup is used where two interference fringe systems are superposed slightly tilted. The axial position of moving solid state surfaces is determined via a phase evaluation. The phase laser Doppler distance sensor offers a position resolution up to 150 nm. In contrast to conventional measurement techniques, such as triangulation, the position uncertainty is independent of the lateral surface velocity. This feature enables precise distance and shape measurements of fast rotating solid state surfaces.