Vacuum ultraviolet quarter wave plates based on SnTe/Al bilayer: Design, fabrication, optical and ellipsometric characterization

Vacuum ultraviolet and extreme ultraviolet polarized light plays a significant role in many applications from materials science and solar physics investigations to optical components development. In this paper, we study the optical performances and the quarter wave retarder properties of aluminum coating capped with SnTe/Al thin film. The measurements have been performed by using a reflectometer properly improved for ellipsometric characterizations. The specimen has been fully characterized at hydrogen Lyman-alpha line (121.6 nm) by deriving the reflectance and the ellipsometric parameters, i.e. the ratio r and the phase difference ?. We found that the SnTe/Al bilayer behaves as phase retarder, although the performances differ from the ideal case. In fact, the polarimetric analysis combined with the optical test at different wavelengths allowed to identify carbon contamination on the top layer and a mild oxidation of the aluminum coating that affect the optical throughput.