Influence of common transparent materials on the accuracy of image-based velocimetry

We discuss the performance of commonly available architectural window materials with respect to the accuracy of optical measurements (e.g. metrology from images, particle image velocimetry, direct image correlation, etc). Window samples were examined for flatness/homogeneity and their performance was quantified by their effect on measurements taken by a three-dimensional velocimetry system. Optical glass performed the best, but also annealed normal and annealed low iron glasses are good, economical options. Plastic-based windows can suffer from damage by laser beams and are only an option if illumination is less important. Polycast acrylic is the best choice within this specific group.