POSITION MEASURING SYSTEM

摘要

Known position measuring systems must be well aligned to provide the necessary resolution for applications such as lithography. The proposed position measuring system (1) comprises a radiation emitting element (2) emitting a radiation beam (3). The radiation beam (3) is diffracted by a diffraction grating (7). First and second diffracted beams (10, 11) having symmetric diffraction orders are reflected back to the radiation-emitting element (2). Meanwhile, the actual frequency of the radiation beam (3) emitting from the radiation-emitting element (2) has been changed so that a beat pattern is produced in the radiation-emitting element (2). By means of a measuring beam (23) this beat pattern is detected in a detector (25).