Fig. 1. Diffraction grating principle. (a) Normal incidence; (b) oblique incidence

Fig. 2. Laser marking. (a) Diagram of system; (b) scanning trace

Fig. 3. Colored samples with different process parameters

Fig. 4. Metallography of grating-like ripple

Fig. 5. Dimensions of laser spot on photopaper and stainless

Fig. 6. Relationship between defocusing and sample width

Fig. 7. Ripple width under different power and defocusing

Fig. 8. Ripple width under different scanning speed and defocusing

Fig. 9. Influence factors of ripple width. (a) Energy density; (b) spot overlapping

Fig. 10. Cubic fitting of least square method of ripple width. (a) Energy density; (b) spot overlapping

Fig. 11. Periodic ripple and single ripple of samples

Fig. 12. Model of periodic ripple structure

Fig. 13. Scanning electron microscope. (a) Sample 1; (b) sample 3

Fig. 14. Sample 4. (a) Scanning electron microscope; (b) mosaic sample

Fig. 15. Color effect of samples under different process parameters. (a) Defocusing; (b) pulse frequency; (c) scanning speed; (d) ripple space; (e) power of the first group; (f) power of the second group

Fig. 16. Metallography of stainless steel surface by multiple line scanning

Fig. 17. Macrographs and micrographs of laser multiple marking

Fig. 18. Scanning electron microscope of sample 8

Fig. 19. Multiple marking samples under different power

Fig. 20. Surface roughness of samples for multiple marking

Fig. 21. Multiple layer color marking model