Theory and experiment in the field of light scattering from optical coatings have been extensively studied and controlled since the 90’s. Indeed surface and bulk theories were developed for substrates and optical coatings, and have revealed great agreement with experiment. Furthermore, angle-resolved apparatuses were built with detection limits close to scattering from the air particles. All these tools have allowed to characterize roughnesses lower than 0.1 nm; also, the microstructure of thin film layers was investigated versus the deposition technologies.
Nevertheless, in the last few years, new challenges for light scattering have merged. Actually, modern deposition technologies with their sophisticated monitoring systems today enable the deposition of large numbers of layers, hence providing complex filters which must be characterized at their working wavelengths or in a wide spectral region. Moreover an increasing demand for micro-structured filters has merged and requires new procedures to discriminate scattering from all micro-devices.
In this context, we have developed in our group at Institut FRESNEL new numerical and metrological tools to satisfy these demands. All scattering facilities were rebuilt and upgraded, sometimes with strongly different principles. In this paper, we will present a rapid overview of these developments, with a focus on broad band scattering metrology (400nm-100nm) with no loss of performance, separation of intrinsic (surface profile) and extrinsic (local defects) roughness, and the control of large-angle scattering in ultra-narrow band filters.
Examples and applications will be given to emphasize all improvements.