Reflectance measurements and optical constants of thin films of ion-beam-deposited SiC, Mo, Mg(2)Si, and InSb and of evaporated Cr have been measured in the extreme-ultraviolet (EUV) spectral region from 49.0 to 200.0 nm. In this spectral region no optical constant data were available for materials deposited by ion-beam deposition. We compared our data with those for bulk samples and for thin films prepared by different techniques. The goal of this research has been to study candidate materials for multilayer coatings in the EUV.