Optical constants of polyimide films in the soft x-ray region from reflection and transmission measurements

Measurements were performed with synchrotron radiation on free-standing, ~300-nm-thick polyimide films in the photon energy range of 40-1350 eV. We evaluated optical constants both from transmission measurements with the Kramers-Kronig analysis and from multiangle reflection measurements by fitting Fresnel equations modified by two different roughness factors for both sides of the film. A thorough error analysis was carried out for both methods. The results agree well within the error barsthereby strengthening confidence in the applied theoretical formalism as well as in the experimental method in this difficult spectral region.