Grating mosaic error evaluation method based on dual-wavelength diffraction spot centroid analysis

To meet the demands of large-range, high-precision grating displacement sensing and high-energy laser systems for large-aperture gratings, grating mosaic technology has become a critical manufacturing process. Addressing the technical challenge that traditional grating mosaic methods struggle to achieve composite detection of the five-dimensional mosaic errors, this paper proposes a method for evaluating grating mosaic errors based on dual-wavelength diffraction spot centroid analysis. By establishing a quantitative mapping model between the five-dimensional mosaic errors and the centroid displacement of the diffraction spots, and utilizing a dual-wavelength laser to decouple the mixed error signals, the centroid coordinates of the spots are extracted using an improved centroid localization algorithm. This verifies the linear relationship between the alignment errors of the mosaic gratings and the centroid positions of the diffraction spots. Experimental results demonstrate that this method can effectively distinguish and measure both angular and displacement errors during the grating mosaic process. Under the condition of a CCD pixel size of 2.4 µm, the achieved detection resolution for angular errors is 0.09 µrad, and for linear displacement errors, it is 0.02 µm. This work provides a non-contact solution for the composite detection of multi-dimensional errors in the fabrication of large-scale mosaic gratings, holding significant application value in the fields of large-aperture grating manufacturing and grating-based displacement sensing.