Variable polarization processing based on femtosecond laser

Micro/nanostructure with a subwavelength period can be induced on the material surface by femtosecond laser, named as Laser Induced Periodic Surface Structure (LIPSS). The uniform LIPSS structure act as a grating that diffracts light, which can display vivid structural colors when illuminating the surface with white light. Structural color with periodic LIPSS structure has strong angle dependence, depends on the direction of the LIPSS structure, which provided us with a new method to realize multi-direction micro/nanostructure processing. By changing the femtosecond laser polarization, we can get the periodic micro/nanostructures in different directions. The polarization controllable femtosecond fabrication can be used for multi-pattern fabrication. The structural color with polarization sensitivity, different patterns could be observed in different directions. Moreover, different from other coloration methods, structural color has inherent stability, which have potential application in the fields of anti-counterfeiting, information storage and dynamic display. In this letter, we introduce a half wave plate to adjust the polarization state of the laser, and realize femtosecond laser variable polarization processing multi-pattern on a stainless steel foil.