A Heterodyne Interferometer for Simultaneous Measurement of Roll and Straightness

A heterodyne interferometer for simultaneous measurement of roll and straightness is proposed for precision linear stages. In the interferometer, the roll and vertical or horizontal straightness are both directly calculated from the phase difference between the measurements and reference signals. The interferometer is composed by a Koster prism, a corner cube, a beam splitter, a 1/2 wave plate, a right-angle prism, a quarter wave plate, a bi-wedge prism and a bi-wedge mirror. The bi-wedge prism is a sensor of roll and straightness. When a dual-frequency laser beam is emitted into the proposed interferometer, six symmetrical laser beams as formed as measurement signals. The beams pass through an almost common path, which improves the stability of the interferometer effectively and minimize the dead path error. The optical configuration of the proposed interferometer is designed and a mathematic model for simultaneously measuring roll and straightness is presented in detail. Finally, an experimental setup is constructed and several experiments are performed to demonstrate the feasibility of the proposed interferometer.