Evolution of femtosecond-laser-induced composite micro-nano structures on copper: mechanisms for anti-reflection and stray light absorption applications

Stray light-induced performance degradation and optical component damage are major bottlenecks restricting the development of high-power, high-stability laser systems. Copper is an ideal heat-dissipation substrate for absorbers due to its ultra-high thermal conductivity. However, its intrinsic reflectivity of up to 94.52% at the 1064 nm laser band makes it unsuitable as a direct stray-light absorber. Here, we fabricate a high-efficiency anti-reflective copper surface via femtosecond laser processing and systematically elucidate its light-absorption mechanism through multidimensional characterization and numerical simulation. The morphology and composition of the fabricated Cu₂O-dominated “oxide layer–groove–nanosphere” composite structure are characterized using integrating sphere reflectometry, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive spectroscopy (EDS). To address the challenge of decoupling quantitative contributions across scales in cross-scale structures, we develop a novel cross-scale finite element model that achieves the first quantitative separation of light absorption contributions from the oxide layer, grooves, and nanospheres. The results show that femtosecond laser processing reduces the 1064 nm reflectivity of copper from 94.52% to 6.38%, with the oxide layer contributing 63.72% of the absorption enhancement as the dominant factor, whose thickness can be precisely tuned by adjusting the laser defocus. This work provides critical theoretical and experimental support for the application of femtosecond laser-modified copper in stray-light absorption devices and promotes the development of high-power laser systems.