  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.
