A two-dimensional grating can be used as a key component in planar encoders for measuring two-dimensional displacements or calibrating coordinate measuring machines. Ideally the two main periodic directions of the grating, the directions along which a translation by a grating period leaves the two-dimensional pattern indistinguishable from the untranslated one, should be perfectly orthogonal; any deviation from orthogonality causes cross-talk errors and necessitates system calibration. We present a method to measure the orthogonality, or the non-orthogonality angle of two-dimensional gratings precisely. This method uses interference fringes generated by diffracted beams of different orders to align the grating's periodic directions, and applies a new measurement strategy to directly measure the non-orthogonality angle by an autocollimator. Compared with traditional optical diffractometry, its angular position alignment is of higher sensitivity and its angle measurement is of lower uncertainty, and the measurement uncertainty is reduced. Orthogonalities of four gratings were measured and the standard uncertainty was 0.28 arcsec. The results agree well with the measurement results of optical diffractometry.
A high-resolution positioning system for linear encoder calibration was developed. The optical sources were stabilized to a femtosecond optical comb for high accuracy and direct traceability to the optical frequency comb. This system showed a control resolution of 17 pm by using an optical zooming interferometer. The stability of the stage was 4.5 nm at 200 seconds, which can be improved by easy modification of optical setup and lasers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.