Anomalies of the optical properties of thin lithium layers and their relation to similar anomalies observed with other alkali metals

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Abstract
The optical properties of very thin layers of lithium were investigated at normal temperature in static ultrahigh vacuum for the spectral region of 1–6 eV. It is shown that these layers exhibit two absorption bands: One, located in the ultraviolet region, is due to interband electron transitions; the other, located in the visible region, cannot be explained by means of classical theories. It is therefore called abnormal. An electron-microscopy study of the configuration of the deposits shows that this abnormal band is due to the granular structure of the deposits, whether they be discontinuous or continuous. In the latter case, they are made up of a two-dimensional distribution of grains on a continuous layer of metal. This structural model accounts for the abnormal optical properties shown, in particular by Mayer et al., on alkali metals, and shows that most of the polarimetric measurements made on these metals in all likelihood involve systematic errors.