A Light Source for the Primary Standard of Wave-Length*

Abstract

A light source for the red cadmium line, 6438.4696 IA, was developed in which the important objections against the cadmium lamp of Michelson type were eliminated. The intensity of the standard line was strong as shown by the short exposure time required to produce an interferometer spectrogram. The effective light-emitting area was 50×2.5 mm2 which was large enough to cover most spectrograph slits. The cadmium standard line was narrow as shown by the interferometer spectrograms. The Doppler-effect broadening was reduced by means of observing the light in a direction perpendicular to that of the discharge current.