Principle of operation

In this set-up the modules U (measuring gauge 5 mm/ 1 µm) and F of the Technical Interferometer up-grade are substituted by the module M1. This module consists of a high precision translation stage driven by a DC motor and a position encoder. The triple reflector Tr2 is mounted on top of the moving part of the stage. The optical arrangement is the same as for the Technical Interferometer. The incoming laser beam is separated into two orthogonally polarised beams by means of the polarising beam splitter (PBS). For the measurement of the position accuracy of module M1 the triple reflector Tr1 stays at a constant position. Both beams are combined again in PBS and deflected to the fringe detection unit where the necessary optical sin, -sin, cos and -cos signals are detected by the photo detectors D1 through D4. These signals are used to determine the travel of Tr2 with an accuracy of 10-6 and a resolution of 0.04 µm. The travel of Tr2 is controlled by the DC motor controller board which is built into a PC. A travel command of e.g. 10.000 mm is launched by the controller. The DC motor starts turning the spindle of the stage. The movement is finished when the number of signals detected by the encoder reaches the desired value. During the movement of the stage, the PC also gathers the interferometer signal giving the exact position of it. A plot of the entire travel range using different kinds of step wise positioning of the stage gives the position accuracy of the translation stage.