Multilayer interference mirrors for the XUV range around 100 eV photon energy

For the first time successful results have been obtained demonstrating interference effects in the reflectance of multilayer films at high photon energies where n = 1 and k is large. Films with 3.5 to 4.5 periods of Au/C and Cu/C were investigated for angles of incidence α = 15° to α = 60° in the wavelength interval 80 to 300A?. The highest near-normal incidence reflectance found was R = 2.7% for Au/C and R = 1.2% for Cu/C at λ ～ 190A?and α = 15°. These values were by a factor of 7 higher than those for a single layered opaque Au film (respectively a factor of 6 for Cu) evaporated under the same conditions. Further improvements appear to be possible. Calculations were performed to guide the investigations and to help the interpretation of the results.