Reflection anomalies related to n = 1

A strong vibration can cause the refractive index, n, to attain values below unity. On the high-wavenumber side of this interval where n matches unity, unexpected reflection anomalies occur which can result in features pronounced enough to dominate the ellipsometric spectra. Even though being of similar shape, these features do not indicate a vibration but indicate sample properties such as the existence of a surface layer or anisotropy, which have to be taken into account when evaluating the spectra. Examples observed with glass, quartz, and a polymer (PTFE) are presented.