Fig. 1. Three-dimensional structure of transmission flat supported by 18×3 adhesive spots

Fig. 2. Deformation of adhesive spots. (a) Transmission flat; (b) bubbles; (c) flow tendency

Fig. 3. Grouping of adhesive spots

Fig. 4. Relationships between PV value of error surface and area ratio of single adhesive spot

Fig. 5. Error surface with single adhesive spot completely detaching. (a) Group A; (b) group B; (c) group C

Fig. 6. First nine Zernike coefficients of error surface with single adhesive spot completely detaching

Fig. 7. Relationships between PV value of error surface and deflection angle of single adhesive spot

Fig. 8. Error surface of single adhesive spot with a deflection angle of 8°. (a) Group A; (b) group B; (c) group C

Fig. 9. First nine Zernike coefficients of error surface with single adhesive spot deflecting 8°

Fig. 10. Processing of images for two typical adhesive spots. (a) Adhesive spot 1 with bubbles inside; (b) binarized of adhesive spot 1; (c) adhesive spot 2 with offset center of gravity; (d) binarized of adhesive spot 2

Fig. 11. Simulation result of degumming error surface in 300 mm aperture

Fig. 12. First nine Zernike coefficients of error surface

Fig. 13. Optical path of Φ300 mm vertical Fizeau interferometer

Fig. 14. Iterative polishing of transmission flat. (a) Initial surface; (b) first polishing; (c) second polishing; (d) third polishing; (e) corrected surface; (f) final surface

Fig. 15. Surface parameters during iterative polishing. (a) PV and RMS values; (b) Seidel aberration coefficients

Fig. 16. Relationships between Seidel aberration coefficients and detachment of adhesive spots. (a) Different radius; (b) different deflection angles

Fig. 17. Repeatability experiments for liquid reference tests