Measurements of the refractive index of yttrium in the 50-1300-eV energy region.

The first experimental results to our knowledge on the refractive index n = 1 - delta + ibeta of yttrium in the extreme-ultraviolet and soft x-ray energy ranges are discussed. To determine the absorptive part beta, transmittance measurements were performed on pure yttrium films in the 50-1300-eV energy region at beamline 6.3.2 of the Advanced Light Source. The dispersive part delta was then calculated from the absorption results by means of the Kramers-Kronig transformation. Compared with prior tabulated values, the new wet of data for the refractive index of yttrium is in better agreement with the sum rules and contains previously unresolved fine structure information in the regions of the M2,3 and M4,5 absorption edges, where yttrium-based multilayer mirrors operate.