Fig. 1. Typical applications of optical freeform surfaces. (a) AR head-mounted display^[7]; (b) off-axis three-mirror system with ultra-wide field of view^[20]

Fig. 2. ZEISS XENOS commercial CMM system^[23]

Fig. 3. Taylor Hopson's commercial profilometers. (a) PGI Freeform profilometer^[27]; (b) LuphoScan profilometer^[29]

Fig. 4. Schematic of optical surface measurement with SOC^[35]. (a) Measurement principle of SOC; (b) scanning path of SOC

Fig. 5. Schematic of Shark-Hartman wavefront detection^[44]

Fig. 6. Schematic of structured light 3D measurement^[47]

Fig. 7. Measurement principle of CGH method^[70]

Fig. 8. Layout of partial-null compensating interferometric system^[92]

Fig. 9. Test principle of Zernike freeform surface in Rochester University^[86]

Fig. 10. Principle of MANI system^[88]

Fig. 11. Schematic of flexible aberration generator used for compensating freeform surface in Anhui University^[91]

Fig. 12. Test principle of ASSI^[106]

Fig. 13. Measurement principle of CSSI^[110]. (a) Schematic of CSSI system; (b) schematic of circular aperture partition

Fig. 14. Irregular sub-aperture partition of interferograms^[119]. (a)(d) Interferograms of biconic surface; (b)(e) resolvable sub-apertures; (c)(f) trimmed sub-apertures of Fig.14(b), (e); (g) ultimate result of sub-aperture partition

Fig. 15. Measurement principle of TWI^[121]. (a) Optical path layout; (b) interferogram array

Fig. 16. Measurement principle of TWI based on tip/tilt mirror^[137]. (a) Optical path layout; (b) interferograms under different angles of tip/tilt mirror

Fig. 17. Layout of common-path TWI system^[138]