The Optical Constants of Sputtered U and a-Si at 30.4 and 58.4 nm

Introduction Optical constants are used to compute the response of a material to light. Previously published optical constants for uranium and a-Si over portions of the extreme ultraviolet (EUV) are questionable. The optical constants of a-Si from peerreviewed literature are not consistent with optical constants calculated from the atomic scattering factors of crystalline Si. The optical constants for uranium and silicon predicted reflectivities higher than we measured. Therefore, we have fit the optical constants of sputtered uranium and amorphous silicon using reflectance measurements. Optical constants are important in the design of optical devices that may be used in multilayer optics, plasma diagnostics, lithography, and space optics. Specifically, we were involved in the design and fabrication of space flight mirrors for the IMAGE explorer satellite. The proper design of these devices depends on reliably knowing the optical properties of many materials. It is also possible to learn about the basic electronic properties of a material by measuring its optical properties. We used the optical constants of many materials to design multilayer mirror coatings for three cameras which were part of the IMAGE mission satellite. An iterative process was used to select the materials and design the multilayer coating because the optical constants were not well known. The multilayer samples that were made were used to obtain the optical constants of a-Si and U at 30.4 and 58.4 nm. We were not certain if the individual optical properties of a-Si and uranium could be distinguished in a multilayer, but we were partially successful in the determination of the optical constants of a-Si and uranium in the EUV. Many different multilayers were prepared to understand the reflective properties of a-Si and uranium; we will only report on multilayers that have an a-Si/U Γ of 0.7±0.03 and have a uranium oxide overcoat. Here Γ is the ratio of the thickness of the top layer to the D-spacing.