Because the incoming beam of EUV light from the ALS is so intense and so tightly focused, scattering can be measured over angles as tiny as a hundredth of a degree. In another technique, the beam is shone directly onto the test mirror through a hole in a circular plate. Most of the beam is reflected straight back through the hole, but scattered light hits the plate, which is riddled with microchannels that produce showers of electrons when struck by photons. These excite a phosphor screen immediately behind the plate to create a pattern that can be viewed directly. This lends confidence to the design, manufacture, and quality control of multilayer mirrors for EUV lithography.
Multilayer coatings have many other applications.