High Stability, Ultrawide, and Extremely High Absorption Aluminum Plane Blackbody Fabricated by Nitrogen‐Assisted Femtosecond Laser

Abstract Aluminum is one of the most commonly used materials for infrared calibration plane blackbodies after black treatment, owing to its high thermal conductivity and lightweight. However, the current structural aluminum plane blackbody fails to achieve high‐absorption performance across an ultrawide spectrum (from UV to long‐infrared waveband) owing to its poor light absorption in the short‐wave infrared region. Herein, a nitrogen‐assisted method is proposed to suppress the plasma‐shielding effect during femtosecond laser processing, which enables the fabrication of sharper micro/nano composite structures on aluminum surfaces. This enhances light absorption in the near‐infrared spectrum while maintaining high absorption in the mid and long‐infrared spectra. Ultimately, a near‐perfect electromagnetic absorbing metal surface is achieved with the absorption of over 98.5% across the waveband from the UV to the long‐infrared region (0.2–25 µm). Furthermore, the fabricated microstructures exhibit excellent mechanical stability and stability at both high and low temperatures. This strategy can effectively overcome the limitations of current aluminum plane blackbodies, thereby expanding their potential applications in infrared calibration, passive radiation cooling, and stray‐light suppression.