Fig. 1. Surface structure of four-level in relation to the two mask patterns.

Fig. 2. Phase distribution of a four-level diffractive lens with misalignment.

Fig. 3. Cross-section intensity distribution of FZL with different misalignment.

Fig. 4. Center offset with the change of misalignment.

Fig. 5. Radius of Airy disk with the change of misalignment.

Fig. 6. PSF with the misalignment of 1.8 μm. (a) is the distribution of PSF, and (b) is the cross-section distribution in the Y direction.

Fig. 7. Diffraction efficiency with the change of misalignment.

Fig. 8. (a) The micrographs of the 80 mm FZL at the outmost zones; (b) is the cross-section profile along the line in (a).

Fig. 9. Depth error of the 80 mm FZL at different positions.

Fig. 10. Test of PSF.

Fig. 11. PSF of the 80 mm FZL. (a) is the test result, and (b) is the calculated result.

Fig. 12. Calculated cross-section intensity distribution of the FZL. (a) is in the X direction, and (b) is in the Y direction.