Crystallographic Regulation of LIPSS Formation on Metal Surface Under Randomly Polarized Nanosecond Laser Irradiation

Laser‐induced periodic surface structures (LIPSS) provide a mask‐free route for fabricating periodic micro/nanostructures. However, the directional energy modulation imposed by linear polarization can often mask crystallography‐dependent material responses, leaving the role of crystallographic characteristics in LIPSS formation insufficiently understood. Here, a randomly polarized nanosecond laser (1064 nm, 7 ns, 700 kHz) is employed with line‐by‐line scanning to weaken the fixed polarization constraint and reveal crystallographic contributions across FCC FeCoCrNiMn high‐entropy alloy, laser‐induced FCC+BCC 310L stainless steel, BCC 430 stainless steel, and Ni‐P amorphous alloy. The crystalline systems exhibit pronounced grain‐selective LIPSS formation, with the formation probability varying strongly with crystallographic orientation. Correlative electron backscatter diffraction (EBSD) analysis further shows that LIPSS orientations preferentially align with projected crystallographic slip traces, indicating that crystallographic slip geometry is closely associated with the directional selection and subsequent development of LIPSS. The FCC, FCC+BCC, and BCC systems exhibit comparable LIPSS spatial periods but progressively reduced continuity and ordering, while grain refinement decreases continuity through increased grain‐boundary (GB)‐related discontinuities. Comparisons with amorphous Ni‐P and linearly polarized irradiation show that LIPSS formation and evolution are governed by coupling between polarization‐controlled directional modulation and crystallography‐mediated surface response. These findings establish a crystallography‐mediated framework for understanding laser‐induced surface self‐organization.