Tabletop spectroscopic ellipsometry for probing optical properties in the extreme ultraviolet

We demonstrate extreme-ultraviolet (EUV) spectroscopic ellipsometry (SE) using a tabletop high-harmonic generation (HHG) source for optical-constant determination. The polarization-resolved system enables accurate retrieval of the complex refractive index n - ik, as validated by measurements on a Nb₂O₅ film and by indirect determination of the optical constants of molybdenum and gold mirrors in the analyzer. This approach provides a compact and versatile platform for precise EUV optical-constant determination and future ultrafast studies.