Fraunhofer Institute for Applied Optics and Precision Engineering IOFDielectrically amplified aluminum mirrors represent an elegant solution for highly reflective layer systems at wavelengths below 200 nm. The achievable reflectivity is determined by the quality of the applied metal layer and its protection against oxidization. On account of their low intrinsic absorption, magnesium fluoride (edge location c. 116 nm) and lithium fluoride (edge location c. 104 nm) are particularly suitable for use as the protection layer. In an optimized vapor depositing process on the Syrus Pro 1100 coating system, a reflectivity of almost 60 % at 115 nm is achieved by using both fluorides.
Initial reflectors with further optimized designs have been realized on a number of recent projects. The measured reflectivity with virtually vertical light incidence was c. 73 % at 115 nm.