The optical constants β, δ of the complex refractive index () of Dy were obtained in the energy range using a novel transmittance method. Si/W/Dy/W films were deposited by dc- magnetron sputtering on Si photodiode substrates, and the transmittance was characterized using synchrotron radiation. The extinction coefficients β of Dy and the transmittance of a Si capping layer and two W interface barrier layers as functions of energy were solved simultaneously using a nonlinear optimization routine. The measured transmittances of the capping and barrier layers were primarily used as indicators for any flaws in the transmittance results. The dispersion coefficients δ of Dy were calculated using the Kramers–Kronig integral, and a complete set of β values required for this integral was obtained by combining the present data with data from the literature. Sum rule tests on Dy show some deficiencies in the present data, which may be attributed to lower film density compared with the bulk value. Similar procedures were applied to previously measured transmittances of , Si/Tb, Si/Nd, and Si/Gd films, where or Si were used as capping layers on those reactive rare-earth films. The improved sets of transmittance values of and Si capping layers were used as input in the optimization routine to solve for more accurate β values of La, Tb, Nd, and Gd. The revised optical constants of these materials, tested for consistency with partial sum rules, are also reported.
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