Dependence of Ultra-Violet Reflection of Silver on Plastic Deformation

Abstract

The change in electrical conductivity of metals with mechanical strain suggests the possibility of a dependence of optical reflecting power on plastic deformation. To study this matter, and to obtain additional evidence with regard to the nature of cold working, the behavior of the minimum of reflecting power of silver in the near ultra-violet (at 3160A according to Hagen and Rubens) was examined for silver surfaces of varying degrees of strain, produced by vigorous and moderate polishing, etching, and electroplating. Reflection curves were obtained by measuring directly, by means of two quartz photoelectric cells, incident and reflected intensities. It is shown that the minimum is very low and lies at 3160A, in accordance with Hagen's and Rubens' measurements, only for highly polished plates. For unstrained surfaces it is shifted to lower wave-lengths by about 20A and the reflecting power rises appreciably. The results presented in the paper, as well as other allied phenomena, are accounted for by assuming a change in the number of free electrons and a consequent change in the index of refraction of the metal.