Laser Doppler Distance Sensor Using Phase Evaluation for Position and Shape Measurements of Rotating Objects

In this article we present a novel optical sensor which allows the simultaneous measurement 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 at a slight tilt. The phase laser Doppler distance sensor achieves a position resolution of 280 nm on rough solid surfaces. 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 on fast rotating solid state surfaces.