Tuning optical response and wettability of aluminum surfaces via polarization-controlled femtosecond laser texturing

Femtosecond laser texturing offers a contactless route to tailor the optical and wetting properties of metallic surfaces. Here, we investigate the effect of laser polarization on commercial mirror-finished Al 5005-H34 by comparing linear and circular polarization under matched fluence and scanning conditions. The processed surfaces were characterized by SEM, optical profilometry, water-contact-angle measurements, EDS, and UV–Vis–NIR reflectance spectroscopy. Polarization produced markedly different surface-evolution pathways. Under linear polarization, the water contact angle increased with fluence, reaching 128.9°, whereas under circular polarization it decreased to 36.4°. Circularly polarized processing also produced a broader roughness evolution and consistently low reflectance, typically below 15% in the visible, while the linearly polarized series showed a much wider reflectance variation. High-magnification SEM revealed localized LSFL in selected circularly polarized regions; in the re-irradiated sample, the characteristic period was 484 ± 41 nm. A secondary channel-patterning step based on circular polarization yielded reproducible superhydrophilic surfaces (θ < 10°) while preserving low reflectance. EDS results indicate that surface chemistry contributes to the wetting response together with the laser-induced morphology. These results demonstrate that polarization is a practical processing parameter for coupling morphology, wettability, and optical response in highly reflective aluminum, with potential relevance for photothermal water management and spatially tailored multifunctional surfaces.