Determination of the Quantity of the Working Element in Spectral Lamps; Methods of Dosage

Abstract

The radiation intensity, its stability, and the reliability of all lamps working with alkali metal vapors depend on the quantity of the introduced metal, its chemical activity in relation to the filling gas, and the material of the lamp bulb. An interdependence between radiation parameters and the quantity of the condensed alkali metal has been known for a long time; for example, its influence on the radiation stability of the positive column of a dc discharge has been described [133]. It was noted that the condensed metal on the cylinder wall causes a nonuniformity in the radiation. The metal can move over the surface and be deposited in various areas of the lamp under the action of the discharge, resulting in an instability of the radiation output. In electrodeless discharges the metal shows a similar behavior but has a stronger influence on the discharge parameters. Therefore, already in the early papers, serious attention was paid to the migration of the metal over the volume of the lamp. To overcome these problems, the excess of metal was captured in a special reservoir away from the discharge itself. The reservoir must have a lower temperature than the lamp. This temperature determines the partial pressure of the alkali metal vapor. In this case the requirements on the dosage of metal are reduced. Nevertheless, for use in quantum devices lamp bulbs without excess of alkali metal are desired. In the beginning of the 1980s, when testing the quantum frequency standards, a number of failures of light sources was noticed, resulting in series of experiments on determination of the optimum amount of rubidium in the lamps. Some methods to control the dosage of a certain amount of metal in the lamp bulbs have been developed and are reviewed in this chapter.