Fig. 1. Roadmap of wide application of optical freeform surface^［11］

Fig. 2. Commercial measurement devices^［11］

Fig. 3. Nanoscale CMM. (a) NMM-1 following the Abbe principle^[25]; (b) NMM-1 picture^[25]; (c) Isara 400 following the Abbe principle^[27]; (d) Isara 400 picture^[27]

Fig. 4. Scanning methods with negligible force. (a) Working principle of AFM^[36]; (b) working principle of STM^[36]

Fig. 5. Working principles of some measurement probes. (a) Multi-probe measurement scheme based on laser focus principle^[26];(b) microscope revolver with multiple probes^[26]; (c) working principle of UA3P-3000^[37]

Fig. 6. Optical profile scanner. (a) Principle of multiwavelength interferometer^[38]; (b) structure of LuphoScan^[38]; (c) principle of chromatic confocal measurement^[39]; (d) structure of NANOMEFOS^[39]

Fig. 7. CGH measurement. (a) Schematic of zero interference of freeform surface CGH^[48]; (b) design of Cat-eye CGH; (c) sample of Cat-eye CGH

Fig. 8. Subaperture measurement methods. (a) Schematic diagram of circular subaperture stitching interferometry^[54];(b) schematic diagram of TWI^[65]

Fig. 9. Adaptive interferometry. (a) Schematic of DM adaptive interferometry^[71]; (b) interference experimental device based on DM^[71];(c) schematic of SLM-based adaptive interferometry^[72]; (d) SLM-based interference experimental device^[72]

Fig. 10. Schematic diagram of phase deflectometry measurement^[77]

Fig. 11. Shack-Hartmann measurement method. (a) Schematic of Shack-Hartmann measurement^[53]; (b) freeform surface measurement by Shack-Hartmann measurement method based on scanning^[90]

Fig. 12. Measurement system based on point laser^[97]

Fig. 13. Scanning electron microscope based on flying cutting machine^[101]

Fig. 14. Schematic of Fizeau interferometer based on diamond turning machine^[94]

Fig. 15. Surface measurement based on PMD^[108]

Fig. 16. Intrinsic feature surface registration method^[132]. (a) Gaussian curvature of lens array; (b) measured results of MLA and f-theta; (c) surface error of microlens after registration; (d) mean curvature of sinusoidal surface array; (e) measured results of composite structure of cylinder and sinusoidal surfaces; (f) surface error of sinusoidal surface array after registration

Fig. 17. Fiducial-aided surface registration method^[134]. (a) Schematic of FA-CAD; (b) accuracy comparison of fiducial-aided registration and ICP

Fig. 18. Form deviation of integrated freeform surfaces after individual measurement and calibration^[169]

Fig. 19. Measurement of integrated freeform surface^[171]. (a) Setup for shape and position measurement; (b) sample; (c) measurement result