The optical properties of thick silicon dioxide on silicon substrate SiO2/Si were fully investigated at the hydrogen Lyman– alpha spectral line. In this case, it was observed that the reflectance measurements are not enough to determine reliable values of the optical constants, but a full polarimetric investigation is required. Thus, the optical constants were determined together with the phase retarder properties by combining EUV reflective ellipsometry and reflectometry. The experimental system used for the measurements is a reflectometer optimized for VUV–EUV spectral range and equipped with a linear rotating polarizer used as an analyzer. The results show the potential of the approach, suitable for cases in which the determination of the ellipsometric parameters, ratio ρ, and phase shift φ, is required for a complete study of the optical and structural properties of the samples. Moreover, it was found that SiO2 behaves as a retarder by introducing a phase difference between the s-and p- polarization components of the incoming light. The phase shift ranges from 18° to 160° depending on the incidence angle. The method, the experimental measurements, the analysis and the results are discussed thereafter.
The EUV reflectometer facility available at the Institute for Photonics and Nanotechnologies-CNR Padua (Italy) has been characterized in terms of Stokes’ parameters at two wavelengths of particular interest for space applications, the hydrogen Lyman alpha at 121.6 nm and 160 nm. The design and the performances of a polarizer based on four gold coated mirrors and coupled with the facility are also described. The whole system consisting of the reflectometer and the polarizer can be used to test mirrors, polarizers and phase retarders in the EUV range by means of the Mueller Matrix formalism, and even to investigate compositions, interfaces and structure of thin films and optical coatings.
High brilliance sources in the EUV spectral range such as Synchrotron and Free Electron Lasers (FEL) are widely used in multiple scientific and technological applications thanks to their peculiar characteristics. One main technical problem of FEL is related to the rejection of high harmonics, seed laser, first stage photons, and diffuse light; in order to improve the quality of the beam delivered by these sources, a suitable optical system acting as band-pass filters is necessary. In this paper we discuss the optical and structure characterization of Nb/Zr and Zr/Nb self-stand transmittance filters, designed for 4.5 nm-20 nm wavelength ranges. In order to understand the properties of these bilayers filters, a campaign of measurements has been planned to be performed on Zr and Nb films on Si3N4 membrane windows and silicon substrates, deposited with e- beam deposition technique. Comparison of the results has been planned too. IMD transmittance and reflectance simulations, together with preliminary AFM and reflectance measurements will be shown in this work.
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