Fig. 1. Sectional view of double freeform-surface lens

Fig. 2. Schematic of energy grid mapping division

Fig. 3. Schematic of construction principle of double freeform-surface

Fig. 4. Geometric analysis method of inner freeform-surface

Fig. 5. Schematic of double freeform-surface lens

Fig. 6. Optimization diagram of target surface

Fig. 7. Three-dimensional model of lens. (a)(c) Three-dimensional structure; (b)(d) cross-sectional view

Fig. 8. Comparison of two freeform-surface lens profiles

Fig. 9. Illumination comparison charts of single freeform-surface lens with different optimization times. (a) Original image; (b) once; (c) twice; (d) three times; (e) four times

Fig. 10. Illumination comparison charts of double freeform-surface lens with different optimization times. (a) Original image; (b) once; (c) twice; (d) three times; (e) four times

Fig. 11. Illuminance curves of single freeform-surface lens with different optimization times. (a) Original image; (b) once; (c) twice; (d) three times; (e) four times

Fig. 12. Illuminance curves of double freeform-surface lens with different optimization times. (a) Original image; (b) once; (c) twice; (d) three times; (e) four times

Fig. 13. Illumination uniformity and system efficiency of different lenses. (a) Single freeform-surface lens; (b) double freeform-surface lens