Spectral selectivity and blackening through direct-write femtosecond micromachining

Controlling broadband light on robust surfaces useful for many applications such as solar receivers. In many of these applications, spectral selectivity is desirable with lower absorptivity and emissivity in the thermal infrared. This paper investigates texturing and direct micromachining method using a femtosecond laser to produce spectrally selective absorbers in the Infrared (IR) spectrum on stainless steel. The relationship between process parameters, surface morphology and optical performance is shown including angular dependent infrared reflectance resulting from coupling to diffractive modes when the feature size approaches the wavelength. The results show that highly effective black surfaces with diffuse reflectances less than 1% in the visible and thermal IR reflectances greater than 90% can be achieved.