Separation detection and correction of mosaic errors in mosaic gratings based on two detection lights with the same diffraction order and different incident angles

Abstract

Grating tiling is an important fabrication technology for large-size gratings. However, when using grating tiling technology to form large-size echelle gratings, the interferometer cannot detect the grating's zero-order diffraction wavefront because the zero-order diffraction light of the echelle grating is weak. This prevents use of the zero-order and non-zero-order diffraction light of the grating to realize separation detection and correction of mosaic errors. To solve this problem, a new method for separation detection and correction of mosaic errors in mosaic gratings based on two detection lights with the same diffraction order but different incident angles is proposed and a mosaic error detection system is designed. Then, the correction steps for mosaic errors are summarized and the error in mosaic error detection system is analyzed. Finally, the measurement uncertainty in detecting the wavefront of the mosaic grating and the mosaic accuracy of the grating wavefront are analyzed. The uncertainty is 0.008λ (λ=632.8 nm) and the mosaic accuracy of the peak-to-valley wavefront is 0.069λ, which shows that high-precision measurements of the wavefront and high-precision mosaic of the wavefront were successfully achieved. The proposed method can be used for the mosaic of all blazed gratings.