The Optical Constants of Sodium and Potassium

Abstract

TOURING the early part of the nineteenth century it was found that *-^ light was partially polarized by reflection from the polished surface of a metal, and also that plane polarized light became, in general, elliptically polarized upon reflection from such a surface.Later this was shown to be due to a relative change in the phase of the two components.The amount of this change was first measured in 1847 by Jamin, 1 who was thus enabled to calculate, theoretically, the index of refraction of the metal used.The next important work along this line was done by P. Drude, 2 who, about 1890, completed a series of measurements from which he determined the optical constants of most of the common metals.A large amount of work has since been done, so that at the present time the optical constants of almost all of the metals are known, with the exception of a few of the more highly oxidizable ones.On account of the rapid oxidation of these, the difficulty has been to obtain a bright metallic surface and to preserve it long enough to examine its optical properties.The few attempts that have been made, while not at all satisfactory, have shown that these metals offer an interesting field for further investigation.In 1898 Drude 3 made a single measurement with sodium light reflected from the molten surface of metallic sodium.This measurement gave an index of refraction of 0.0045 which, if correct, means that light travels 220 times as fast in that metal as in air.After making due allowance for some possible errors, which Drude admits might have lowered his result, he says that the index could not be greater than 0.054.But this value is still remarkably low compared to the indices of other metals.Since Drude's value of the index of sodium was made with sodium light, the question arises is there any connection between the low value of the index and the fact that the light used was of a wave-length peculiar 1