FUV- EUV Polarimetric System Development

The generation and control of linearly and circularly polarized light in the far ultraviolet (FUV) and extreme ultraviolet (EUV) spectral regions are required in different frontiers research and technological areas ranging from material science, where the nature of the beam plays a fundamental role in the light-matter interaction, to optical components developments including devices for manipulation of the light polarization state. This has pushed researchers to examine and outline new optical elements as optical polarizers and quarter-wave retarders (QWRs) specifically designed for this spectral range and thought to be used in proper optical arrangements in order to provide valuable information about physical and optical properties of materials and optical coatings. In this thesis, we present an EUV reflectometer facility located in the Institute for Photonics and Nanotechnologies-CNR Padua (Italy) which was implemented for polarimetric measurements within a suitably wide spectral range (90-160 nm) where some important spectral emission lines are, as the hydrogen Lyman alpha 121.6 and Oxygen VI (103.2 nm) lines. The development part focuses on the design and fabrication of an optical linear polarizer based on four reflection gold-coated mirrors to be inserted in the EUV reflectometer optical path. In this way, the facility can be used as an EUV spectroscopic ellipsometric system. The robustness of the methodology and the system were tested to characterize the optical and structural properties of a single layer aluminum mirror as quarter wave retarder (QWR) by deriving its amplitude component tanψ=r_p/r_s and phase difference δ. The second part of the thesis comes from the desire to explore new optical materials employed as a capping layer for optical coatings in the far ultraviolet (FUV) and extreme ultraviolet (EUV) spectral regions. The materials are mostly absorptive in these spectral regions, thus the availability of high-performance optical coatings for the short wavelengths is quite restricted for this reason. In this part, we present a phase retarder optical component based on SnTe/Al bilayer covering the spectral range between 80 nm and 160 nm. The measurements have been performed using an EUV reflectometer facility improved for ellipsometric measurements. The specimen has been fully characterized at hydrogen Lyman–alpha line (121.6 nm) in terms of reflectance and ellipsometric parameters, i.e. the ratio r, ratio of the Fresnel coefficient, and the phase difference δ introduced between the -s and -p reflected components. To our knowledge, such structure based on SnTe haven’t been studied as capping layer for a wide spectral range in the vacuum ultraviolet, although the throughputs are not those expected for this structure. The drop-in performances are attributed to the carbon contamination on the sample surface identified by additional reflectance measurements at 160 nm wavelength. The results also confirm the potentialities and the advantages of such non-invasive optical approach. Lastly, the whole system consisting of the reflectometer and the polarizer could be particularly useful as diagnostic tools in EUV ellipsometry field. The system can be a relatively simple complement to large-scale facilities and can be applied to test optical components by deriving their efficiency, determining the Mueller Matrix terms, and even to the analysis of optical surface and interface properties of thin films. In addition, the QWRs developed in this framework could be used in other experimental applications for generating EUV radiation beams of suitable polarization, for characterizing and controlling the polarization state of EUV radiation beams and to be inserted in an ellipsometric scheme in order to characterize optical devices.