Origins of light scattering from thin film coatings

The light scattering properties of multilayer coatings is substantially more complex than that of single surfaces. Yet new experimental methods and modeling techniques enable multilayer scattering to be investigated and analyzed in detail. In this article, the dominating factors influencing the scattering of near infrared suppressing interference filters are discussed. This is done by combining angle resolved light scattering measurements at different wavelengths with roughness metrology and simplified theoretical models. The impact of different sources of scattering, in particular substrate and coating roughness, interference effects, and local defects, are discussed in a quantitative manner. It will be demonstrated that the impact of nodular defects is negligible while the impact of interference effects is not. •The scattering of near infrared suppressing edge filters was investigated in detail.•Angle resolved scattering was measured at different wavelengths.•The main causes of scattering were roughness, interference effects, and defects.•Interference effects can strongly enhance the scattering properties.•The impact of nodular defects with sizes of about 5μm was negligible.•Scatter maps were performed to detect and classify defects.