Fig. 1. Setup of two-beam interference lithography for MLD gratings. L, Kr⁺ laser; M, mirror; PM, piezo mirror; λ/2, polarization rotator (e.g., half-wave plate); PBS, polarizing beam splitter; SF, spatial filter; SH, shutter; OAP, off-axis parabolic mirror; S, substrate with mount; RG, reference grating; G, ground glass.

Fig. 2. Reflective two-beam laser static interference lithography station for MLD grating fabrication.

Fig. 3. Processing steps of manufacturing MLD grating.

Fig. 4. (a) Schematic diagram of the light field diffraction law in the exposure system. (b) Local figure error example with MSF and HSF errors. (c) Actual light field photo caused by the example surface. (d) Theoretical prediction result calculated by the proposed model. (e) Sine filter characteristic of the light field diffraction law.

Fig. 5. The frequency error division scheme for the grating exposure system.

Fig. 6. Surface shape error distribution of the off-axis parabolic mirror under the traditional polishing process. (a) The figure error of the off-axis mirror measured by using a 4" Zygo interferometer. (b) The MSF error filtered according to the model specification and a photo of the light field distribution. (c) The HSF error measured by a Zygo white light profiler with a 20 × lens and a photo of the microscale grating mask. (d) 1D-PSD curves.

Fig. 7. (a) MRF and “magic” angle step technology. (b) Small tool processing and smooth pseudorandom path.

Fig. 8. Surface shape error distribution of the off-axis parabolic mirror after the combined polishing process. (a) Using a 4" Zygo interferometer to measure the figure error of the off-axis mirror. (b) The MSF error filtered according to the model specification and a photo of the light field distribution; (c) The HSF error measured by a Zygo white light profiler with a 20 × lens and a photo of the microscale grating mask. (d) 1D-PSD curves.

Fig. 9. Diffraction wavefront and efficiency distribution of the MLD grating. (a) –1st order diffracted wavefront. (b) Zeroth order diffracted wavefront. (c) +1st order diffracted wavefront. (d) The diffraction efficiency map of the MLD grating at 1740 l/mm shows excellent uniformity of diffraction efficiency over the entire aperture for 1053 nm (Ave = 98.1%, σ = 0.3%, Max = 98.6%). (e) A 200 mm × 150 mm, 1740 l/mm MLD grating designed for use at 1053 nm, fabricated by reflective lithography.