Fig. 1. Schematic diagram of ion beam figuring

Fig. 2. Schematic diagram of coordinate transformation in tilted incident ion beam figuring process

Fig. 3. Peak ion beam density varying with the incident angle

Fig. 4. Normalized beam density distribution versus incident angle (0°, 15°, 30°, 45°, 60°)

Fig. 5. Impact curves of the ion beam incident angle. (a) Peak and volumetric removal rates versus the incident angle; (b) figuring accuracy and dwell time versus the incident angle

Fig. 6. Impact of local curvature on the ion sputtering

Fig. 7. Impact of surface gradient on the ion sputtering. (a) Impact of surface gradient on incident angle; (b) secondary sputtering

Fig. 8. Impact of the incident angle on the ion sputtering

Fig. 9. Surface roughness results. (a) Interferometer test results; (b) atomic force microscope test results

Fig. 10. Tilted incident experiments of ion beam. (a) Experimental photo; (b) surface error map

Fig. 11. Surface roughness variation curve. (a) Variation curve with the interferometer test results; (b) variation curve with the atomic force microscope test results

Fig. 12. Surface roughness variation curves with different incident angles

Fig. 13. Process flowchart based on the tilted incident ion beam figuring

Fig. 14. Initial surface accuracy and surface roughness of the single crystal silicon cylindrical mirror. (a) Surface error map; (b) surface roughness results with the interferometer test; (c) surface roughness results with the atomic force microscope test

Fig. 15. Surface accuracy and surface roughness with tilted incident ion beam figuring. (a) Surface error map; (b) surface roughness results with the interferometer test; (c) surface roughness results with the atomic force microscope test

Fig. 16. Surface accuracy and surface roughness with vertical incident ion beam figuring. (a) Surface error map; (b) surface roughness results with the interferometer test; (c) surface roughness results with the atomic force microscope test