Broad-Band Ultra-Low-Reflectivity Multiscale Micro–Nano Structures by the Combination of Femtosecond Laser Ablation and In Situ Deposition

Functional surfaces with broad-band ultralow optical reflection have many potential applications in areas like national defense and energy conversion. For efficient, high-quality manufacturing of material surfaces with antireflection features, a novel machining method for multiscale micro–nano structures is proposed. This method can enable the collaborative manufacturing of both microstructures via laser ablation and micro–nano structures with high porosity via in situ deposition, and it can simplify the fabrication process of multiscale micro–nano structures. As a result, substantially improved antireflection properties of the treated material surface can be realized by optimizing light trapping of the microstructures and enhancing the effective medium effect for the micro–nano structures with high porosity. In ultraviolet–visible–near-infrared regions, average reflectances, as low as 2.21 and 3.33%, are achieved for Si and Cu surfaces, respectively. Furthermore, the antireflection effect of the treated surface can also be extended to the mid-infrared wavelength range, where the average reflectances for the Si and Cu surfaces decrease to 5.28 and 5.18%, respectively. This novel collaborative manufacturing method is both simple and adaptable for different materials, which opens new doors for the preparation of broad-band ultra-low-reflectivity materials.