Abstrakt der Dissertation: This publication-based dissertation is dedicated to the accurate metrological characterization of optical diffuse transmission. Its macroscopic representation, translucency, as one of the four attributes for describing an object’s optical appearance, is gaining increasing interest in fields of quality control, climate monitoring, computer graphic rendering, etc. Thus, the need for definition of the corresponding measurand, bidirectional transmittance distribution function (BTDF), and for standardization of its measurement procedures is increasing. In this work, I present the results achieved in my research period as PhD student in the Working Group 4.51 “Reflection and Transmission” at Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute. Major results were published as peer-reviewed scientific journal papers and are exhibited in this work, along with an extensive introduction to the theoretical background and the applied methodology, followed by additional information and discussion.
Two main aspects of accurate BTDF characterization are focused on in this work. The first one is the development of a new goniospectrophotometric facility for multidimensional BTDF measurement. This facility aims to complement the existing research and calibration capabilities of the working group in the field of optical reflection and transmission. In the future, it will provide the primary realization of quantities related to optical diffuse transmission such as BTDF in the spectral range from ultraviolet to near-infrared. Major features of the facility, such as sample- and detector-positioning, configurations of irradiation and detection systems, etc., are paid special attention to after a thorough study of other relevant goniospectrophotometers worldwide. The flexibility of switching measurement scheme between under- and over-irradiation using this new facility allows for further study on the flux-dependent transmittance, aiming at extension and generalization of the BTDF definition for strongly scattering materials.
Another focus of this work is the metrological characterization of diffusers with different scattering behaviors, exhibiting quasi-Lambertian, Gaussian, and square-shaped tophat BTDF distributions. Multiple interlaboratory comparisons were conducted between European metrology institutions, universities, and industrial partners. Measurement data were analyzed using statistical approaches, revealing current BTDF measurement capabilities and providing insights for a future Key Comparison.