Using light scattering to investigate damage-relevant imperfections of surfaces, coatings, and bulk materials

Light scattering is one of the loss mechanisms of optical components. It is caused by intrinsic and extrinsic imperfections such as roughness, index fluctuations, and bulk or surface defects that can all play critical roles for the laser stability of optical components. Light scattering metrology has proven to be a versatile non-destructive technique to characterize imperfections. Information can be retrieved with high sensitivity even over large areas. The total scatter levels or scattering coefficients provide information about scatter losses whereas the angle resolved scattering provides detailed information about the sources of scattering. An overview of the instruments developed at Fraunhofer IOF will be given and a variety of examples of application will be discussed comprising roughness and defect maps of lithography optics, investigations of bulk scattering of optical materials, and enhanced scattering through thickness errors of interference coatings.