Femtosecond laser production of metal surfaces having unique surface structures that are broadband absorbers

Abstract

Femtosecond laser induced modification of surface structure and the optical properties of metals are studied. A Ti:sapphire femtosecond laser is used for ablating bulk aluminum 2024 T3 alloy and highly pure neutron activation quality gold metal samples at different laser irradiation parameters. The ablation parameters are optimized for the two metals to form a low reflection surface in the wavelength range of 0.3–50 μm. “Black aluminum” and “black gold” metal surfaces are formed upon laser ablation, having a unique surface structure with micro- and nanosized features. Sample analysis is performed by several characterization techniques like scanning electron microscope, energy dispersive x ray, profilometry, and integrating sphere reflectance measurements. Correlation is drawn between the laser ablation parameters and the formed surface structure and its properties. The reflection of light is found to depend primarily on the surface structure (roughness) of the highly modified metal surfaces.