Development of a spectral ellipsometer for the investigation of the optical properties of mono- and polycrystalline UO 2

This is the authors' abstract. We don't add key points for this paper.

Accurate optical characterization is essential for uranium dioxide (UO 2 ) for understanding the laser-matter interaction phenomena involved in the material characterization techniques used in nuclear fission research. In this study, we investigate the optical properties of mono- and polycrystalline UO 2 using a custom spectral ellipsometer, complemented by transmission measurements. The instrument performances are assessed on Si and Ge wafers combined with silica thin film characterization. Our results reveal a refractive index of 2.3 and exhibit a band gap at 2 eV with strong absorption below the band gap. While transmission measurements confirm the band gap position, they indicate absorption levels 4 to 40 times lower than those derived from ellipsometry. This disparity, already reported in the literature, is observed on the same type of sample, implying a thermodynamically non-stable surface.