Wettability Change of Copper by Controlling Area Fraction of Laser-Ablated Surface

In this work, we present a single-step, chemical-free method to tune the wettability of copper surfaces using nanosecond and picosecond laser irradiation. By controlling the area fraction of the laser-ablated surface, a continuous adjustment of the static water contact angle from nearly 0° to over 130° is achieved. The wettability evolution is interpreted using classical Wenzel and Cassie–Baxter models, where the ablated area fraction serves as an effective geometrical parameter governing the solid–liquid interaction. Importantly, similar wettability behavior is observed for both nanosecond and picosecond processing despite significant differences in surface roughness, indicating that roughness alone is insufficient to describe the wetting response. Instead, the ablated area fraction provides a more consistent and measurable descriptor of wettability. In addition to wettability modification, correlated changes in optical appearance, primarily manifested as surface darkening, are observed with increasing ablation. These changes are quantified using grayscale-based metrics and are attributed to combined effects of surface morphology and oxidation rather than deliberate color engineering. The proposed approach offers a simple, reproducible, and scalable route for functionalizing copper surfaces, where wettability can be controlled through a single geometrical parameter.