Optical constants of materials in the EUV/soft x-ray region for multilayer mirror applications

The response of a given material to an incident electromagnetic wave is described by the energy dependent complex indexof refraction n = 1 {minus} {delta} + i{beta}. In the extreme ultraviolet(EUV)/ soft x-rayspectral region, the need for accurate determination of n is driven by activity in areas such as synchrotron based research, EUV/ x-ray lithography, x-ray astronomyand plasma applications. Knowledge of the refractive index is essential for the design of the optical components of instruments used in experiments and applications. Moreover, measured values of n may be used to evaluate solid state models for the optical behavior of materials. The refractive index n of Si, Mo and Be is investigated in the EUV/ soft x-rayregion. In the case of Si, angle dependent reflectance measurements are performed in the energy range 50--180 eV. The optical constants {delta}, {beta} are both determined by fitting to the Fresnel equations. The results of this method are compared to the values in the 1993 atomic tables. Photoabsorption measurements for the optical constants of Mo are performed on C/Mo/C foils, in the energy range 60--930 eV. Photoabsorption measurements on Be thin films supported on silicon nitride membranes are performed, and the results are applied in the determination of the absorption coefficient of Be in the energy region 111.5--250 eV. The new results for Si and Mo are applied to the calculation of normal incidence reflectivities of Mo/Si and Mo/Be multilayer mirrors. These calculations show the importance of accurate knowledge of {delta} and {beta} in the prediction and modeling of the performance of multilayer optics.