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Published on Jan 2, 2013
(Adolf Cortel, December 2012) The video shows how the sodium doublet observed in the emission of a low pressure sodium lamp coincides with the doublet due to absorption in Fraunhofer's lines. The potassium doublet is easily observed (in the IR) with potassium iodide in a flame. The measurement of the wavelength difference in both doublets can be done with a Fabry Perot interferometer from the positions where the interference fringes overlap when one mirror is displaced.