Design of a gonio-spectro-photometer for optical characterization of gonio-apparent materials

Abstract : Gonio-apparent surfaces, characterized by large variations in optical properties with small variations in detection or illuminating directions, have a huge appeal for industrial product for aesthetic reasons. This work is dedicated to the design of a gonio-spectrophotometer (OptiMines goniometer) adequate for analyzing the light reflecting behavior of these challenging surface aspects. Such optical characterizations are useful data for realistic rendering of such surfaces in computer graphics but also for new product development and quality control in industrial manufacturing. To reach the four degrees of freedom necessary to cover the entire reflecting hemisphere, the designed geometrical setup favors movements of the sample so that illuminating and detection arms only carry one degree of freedom each. Having only one degree of freedom on each optical arm enables an easy installation of precise optical systems that leads to a very high directional accuracy for small arm dimensions. High directional accuracy is essential for fine analysis of gonio-apparent surfaces in order to prevent signal averaging with out-of-direction beam, in particular when the property change is abrupt. The analysis of both diffuse and gonio-apparent materials demonstrates the performance in surface metrology provided by this new device.