Beam characterization of a microfading tester: evaluation of several methods

Microfading testing allows to evaluate the sensitivity to light of a specific artwork. Characterization of the illumination spot is important to determine its shape, dimensions, light distribution, and intensity in order to limit and account for possible damage. In this research the advantages and disadvantages of several methods used to determine the beam shape and intensity profiles are described with the aim of providing various options to microfading researchers interested in characterizing their irradiation spots. Conventional and imaging methods were employed and are compared in terms of their accuracy, cost, reliability, and technical features. Conventional methods consisted of an aperture technique using aluminium foil and four different materials namely stainless steel, silicon, muscovite, and Teflon used as sharp edges. The imaging methods consisted of digital photography of illumination spot, direct beam measurement using a CMOS camera, and direct beam measurement using a laser beam profiler. The results show that both conventional and imaging methods provide beam width measurements, which are in satisfactory agreement within experimental error. The two best methods were direct measurement of the beam using a CMOS camera and sharp-edge procedure. MFT illumination beam with a CMOS camera followed by a determination of the beam diameter using a direct method, more specifically one involving a sharp-edge technique.