Polarization properties of Mo/Si multilayers in the EUV range

We investigate polarization properties of two novel reflective Mo/Si multilayers (ML) in the EUV range using polarized synchrotron radiation at the BESSY-II storage ring facility. One of the Mo/Si ML is used as a retarder, the other one as an analyzer within the experimental setup of the BESSY soft-x-ray polarimeter. The analyzer multilayer is characterized by performing reflectivity measurements with s- and p-polarized light as a function of the incidence angle for different wavelengths. The characterization of the retarder multilayer consists of reflectivity measurements with s- and p-polarized light as a function of the wavelength for three different angles near normal incidence. In addition the phase retardance on reflection was determined for one angle of incidence as function of wavelength. Uncertainties of the phase retardance are estimated via the block bootstrap method. As an additional by-product of the ML characterization the Stokes parameters of the beamline could be determined. With the 8-axis BESSY polarimeter we have measured the complex reflection coefficients for the first time and established this ellipsometry technique as an additional probe to characterize multilayer optical elements.