Resonance Radiation of Sodium Vapor Excited by one of the D Lines
Robert Williams Wood, Fred L. Mohler
TPHE purpose of this investigation was to study the resonance spec--*-trum of sodium vapor when the resonance was excited by a single D line.In a paper on " Resonance Radiation of Sodium Vapor "* published by one of us in 1905, it was shown that if a bulb containing pure sodium vapor was illuminated by light from a sodium flame, the vapor emitted a yellow light which spectroscopic analysis showed to be identical with the exciting light, in other words, the two D lines.It was suggested at this time that it would be interesting to see if both D lines appeared when the vapor was illuminated by a single D line.This would determine whether the mechanisms that give rise to the D lines are separate or in some way connected.In 1914 this experiment was tried by Wood and Dunoyer. 2 This experiment was made possible by the discovery of a polarization method of separating close spectral doublets that eliminated the great loss of light involved in a high-power monochromator, but even with this method the resonance light is very faint.The spectrum of resonance excited by D 2 was photographed with exposures varying from 10 to 15 hours.The majority of the plates showed only the D 2 line, but owing to under exposure Di would not have been visible if it was less than one fourth of the intensity of D 2 .Some plates indeed showed both Di and D 2 , but the presence of Di in the exciting light was judged to be the cause of this.Imperfections in the optical system made it impossible to entirely remove Di from the exciting light and as it was sensitive to temperature changes the nature of the transmitted light sometimes changed during an exposure.It was concluded that sodium resonance excited by D 2 consisted of D 2 alone, but the results admit of two other possibilities.Di light may always be present though much fainter than D 2 , or it may only appear under certain conditions.Other resonance phenomena show that the radiation centers in sodium are not entirely independent.One of us 3 showed in 1905 that excitation 1
Physical Review•Jan 1, 1918•37 citations