Near-unity broadband omnidirectional emissivity via femtosecond laser surface processing

TL;DR

This paper demonstrates a scalable femtosecond laser surface processing method to create aluminum surfaces with near-unity broadband omnidirectional emissivity, suitable for thermal management and radiative cooling applications.

Contribution

It introduces a novel laser processing approach to achieve near-perfect broadband omnidirectional emissivity on metals, combining surface features and oxide layers.

Findings

Achieved near-unity broadband omnidirectional emissivity on aluminum surfaces.

Identified microscale surface features and oxide layers as key to emissivity enhancement.

Validated results through experiments and full-wave simulations.

Abstract

It is very challenging to achieve near perfect absorption/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.