Reducing machine-ruling grating wavefront value by compensating grating substrate surface error in real time

To improve the grating wavefront quality especially the grating size, which is more than 1 m, we provide a method based on conical diffraction theory and grating groove active control technology to correct the grating substrate surface error. We apply the grating groove active control technology to carry out an echelle grating ruling experiment whose line density is 79 lines/mm in 36th order. Compared with the grating substrate surface error, the grating wavefront value reduces from 0.105 λ to 0.056λ i.e., decreases by 47%. The experimental result proves that the grating substrate surface error compensation method can be used to improve the grating wavefront quality effectively.