Abstract
The spectral bidirectional reflectance distribution function (BRDF) of metals plays an important role in industrial processing involving laser-surface interaction. In particular, in laser metal machining, absorbance is strongly dependent on the radiation incidence angle as well as on finishing and contamination grade of the surface, and in turn it can considerably affect processing results. Very recently, laser radiation is also used to structure metallic surfaces, in order to produce many particular optical effects, ranging from a high level polishing to angular color shifting. Of course, full knowledge of the spectral BRDF of these structured layers makes it possible to infer reflectance or color for any irradiation and viewing angles. In this paper, we present Vis-NIR spectral BRDF measurements of laser-polished metallic, opaque, flat samples commonly employed in such applications. The resulting optical properties seem to be dependent on the atmospheric composition during the polishing process in addition to the roughness. The measurements are carried out with a Perkin Elmer Lambda 950 double-beam spectrophotometer, equipped with the Absolute Reflectance/Transmittance Analyzer (ARTA) motorized goniometer.
Highlights
Laser surface processing techniques on metals are a subject of great interest from both a scientific and industrial standpoint, since they can allow faster machining times and yield more precise finishing properties than the mechanical counterpart
The bidirectional reflectance distribution function (BRDF) is only one of the parameters considered in [4] to evaluate visual appearance, where texture properties have to be taken into account, it still is the main measurable feature in characterizing surfaces, and it can give a full insight on the optical properties of a surface finish
BRDF is defined as a differential quantity, the use of finite quantities is needed for a definition of BRDF that can be applied in real measurement situations, typically with the rotation of the sample along one or two axes and a movable detector with an aperture area Ad that can revolve around the test object
Summary
Laser surface processing techniques on metals are a subject of great interest from both a scientific and industrial standpoint, since they can allow faster machining times and yield more precise finishing properties than the mechanical counterpart. They can be used to obtain several number of interesting features, like controlled microstructures for enhancing glues adhesion [1], coloring via oxidation phenomena, and surface polishing. The BRDF is only one of the parameters considered in [4] to evaluate visual appearance, where texture properties have to be taken into account, it still is the main measurable feature in characterizing surfaces, and it can give a full insight on the optical properties of a surface finish
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