Questions about the Mayer-El Naby optical anomaly in potassium

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Abstract
The large, optical-absorption anomaly in the reflection spectrum of potassium, discovered by Mayer and El Naby has a threshold near 0.6 eV and maximum near 0.8 eV. The failure of other workers to reproduce this effect has led to a premature conclusion that it was an experimental artifact. The recent discovery by Harms of how to reproduce it in a controlled way reestablishes the need for a satisfactory explanation. Since the anomaly is turned on by the presence of a KOH surface layer, we report transmission measurements on KOH between 0.5 and 1.1 eV. These show that absorption in KOH cannot be the cause. A number of other extrinsic mechanisms are also considered. Finally we entertain the possibility that the absorption is intrinsic to the metal. This would require potassium to be optically anisotropic. If the direction of the optic axis is influenced by the presence of the KOH layer, a quantitative account of the diverse observations is possible. Two critical experiments are proposed which may distinguish intrinsic and extrinsic mechanisms.