Near-unity broadband omnidirectional emissivity via femtosecond laser surface processing

It is very challenging to achieve near perfect absorption or emission that is both broadband and omnidirectional while utilizing a scalable fabrication process. Femtosecond laser surface processing is an emerging low-cost and large-scale manufacturing technique used to directly and permanently modify the surface properties of a material. The versatility of this technique to produce tailored surface properties has resulted in a rapidly growing number of applications. Here, we demonstrate near perfect, broadband, omnidirectional emissivity from aluminum surfaces by tuning the laser surface processing parameters including fluence, pulse count, and the ambient gas. Full-wave simulations and experimental results prove that the obtained increase in emissivity is mainly a result of two distinct features produced by femtosecond laser surface processing: the introduction of microscale surface features and the thick oxide layer. This technique leads to functionalized metallic surfaces that are ideal for emerging applications, such as passive radiative cooling and thermal management of spacecraft. Surfaces with wide-angle high emissivity in the infrared spectrum are important for applications in radiative cooling, thermophotovoltaics, and spacecraft thermal management. Here, near perfect, broadband, omnidirectional emissivity is realized via scalable laser surface processing of aluminum.