Fig. 1. Schematic diagram of the proposed system. (a)Structure diagram of application system; (b)structure diagram of system principle

Fig. 2. Schematic diagram of the incident light. (a) Upward incident light; (b) downward incident light

Fig. 3. Schematic diagram for the torsion angle. (a) The spots′ schematic diagram when the torsion angle is 0; (b) the spots′ schematic diagram when the torsion angle is 扭转角示意图。(a)扭转角为0时的斑点示意图；(b)扭转角为 时的斑点示意图

Fig. 4. Physical picture and simulation charts of the lens array. (a) Physical picture of the lens array; (b) size of the lens array; (c) top view of the lens array; (d) side view of the lens array

Fig. 5. Experimental set-up

Fig. 6. The seventh group of light spots

Fig. 7. Fitting of adjacent spots

Fig. 8. Spot array images with different β_y when β_x = 0; (a) β_y = 250″；(b) β_y = 500″

Fig. 9. Measurement results in the Y direction. (a) Centroid spacing changing with β_y; (b) error curves in comparison with autocollimators

Fig. 10. Spot array image with different β_x. when β_y = 0. (a) β_x = 250″; (b) β_x = 500″

Fig. 11. Measurement results in the X direction. (a) Centroid spacing changing with β_x; (b) error curves in comparison with autocollimators

Fig. 12. Curve of centroid varying with inclination angle in the Z direction

Fig. 13. Contrast error compared with the results measured with autocollimator and spot spacing in X and Y directions