Precision fringe period metrology using an LSQ sine fit algorithm.

High-precision grating fabrication is a precondition of grating-based displacement measurement techniques. Likewise, the value of high-precision fringe period is an essential parameter in the grating fabrication process, especially in scanning beam interference lithography. In this paper, a procedure for measuring the fringe periods of interference beams is introduced. The procedure includes signal acquisition and signal processing. The precisions of both the configuration for acquisition and the algorithm for processing are discussed. Experiments for fringe period measurement are also conducted, and an average value of 564.374 nm with a standard deviation of 1.5 pm is obtained, reaching a repeatability of 2.6 ppm. The value of precision period lays a solid foundation for the fabrication of high-precision gratings.