Fig. 1. Design results and imaging quality analysis of freeform surface prism. (a) Optical path diagram of the freeform surface prism system; (b) MTF curves of the optical system at 25 ℃

Fig. 2. Machining errors of freeform surface prism system. (a) Inter-surface spacing error; (b) surface tilt error; (c) surface decenter error

Fig. 3. Influences on MTF of the optical system when freeform surface 1 and 2 experience perturbation. (a) Freeform surface 1 experiences decenter perturbation in the Y direction; (b) freeform surface 2 experiences decenter perturbation in the Y direction; (c) freeform surface 1 experiences tilted perturbation in the X direction; (d) freeform surface 2 experiences tilted perturbation in the X direction; (e) air spacing 1 experiences perturbation in the Z direction; (f) air spacing 2 experiences perturbation in the Z direction

Fig. 4. Assembly diagram of infrared freeform surface prism

Fig. 5. Finite element analysis of freeform surface prism

Fig. 6. Assembly diagram infrared freeform surface prism

Fig. 7. Ultra-precision compensation machining process flow of prism

Fig. 8. Measurement schematic diagram of prism angle error. (a) In-situ measurement; (b) off-machine measurement

Fig. 9. Schematic diagram of inspection fixture

Fig. 10. Detection results for the infrared freeform surface prism. (a) Close-range imaging ; (b) original image and its long-range imaging