Light scattering characterization of optical components – BRDF, BTDF and scatter losses

Light scattering caused by imperfections of optical components can critically affect the performance of optical systems in terms of losses and image degradation. Because of the numerous potential sources of scattering such as roughness, surface and sub-surface defects, bulk inhomogeneities, as well as coatings, scattering properties must be carefully specified and measured at the wavelengths of application. Bidirectional Reflectance and Transmittance Distribution Functions (BRDF / BTDF) are used to quantify the angle resolved scattering properties. The data can be used as an input for optical engineering software just as FRED, ASAP, ZEMAX for stray light modeling. In addition, analyzing the scattered light can provide valuable information about the relevant imperfections. The presentation provides an overview of instrumentation for light scattering measurements at wavelengths ranging from the visible to the extreme ultraviolet and the infrared spectral regions. Examples of applications will be discussed ranging from superpolished mirrors to diffraction gratings, interference coatings, and black absorbing coatings