The measurement of light scattering from optical components has received increased attention in the last decade. In addition to being a serious source of noise, light scattering can lead to a reduced optical throughput, degrade the imaging quality, or cause straylight in optical systems. On the other hand, the high sensitivity towards small imperfections and inhomogeneities makes light scattering measurements a powerful inspection tool. Measured light scattering is a good indicator of the surface quality and can be used to characterize the surface roughness or local defects. After an introduction of the main scattering quantities as well as their standardization, this chapter will focus on the instrumentation used to characterize light scattering and provide various application examples ranging from the light scattering based roughness characterization of supersmooth substrates to the roughness evolution of different multilayer coatings and its impact on the scattering properties.
