Pulsed hollow cathode light sources

Abstract

Spectroscopic measurements of the light emitted by pulsed hollow cathode lamps have been made as a function of cathode material and geometry, buffer gas and buffer gas pressure, and the size and shape of the exciting current pulse. From these observations the following generalizations can be made. The source exhibits the same general properties with any metal cathode material and with any geometry. Excitation increases with increasing peak current between 30 and 1500 A and is essentially independent of the shape of the current pulse as long as the pulse is not oscillatory. It increases with increasing buffer gas pressure over the range of stable operation of the source between 5 and 50 torr. Buffer gases with high ionization potentials increase ionization while molecular gases depress it. Time-resolved measurements show that the excitation temperature in the afterglow decreases almost linearly with time. Electron density is independent of pressure but increases linearly with increasing peak current. Electron density also decreases linearly with time in the afterglow. Finally, lines from higher ionization stages appear earliest in the light source output. The dependence of excitation and ionization on pressure, buffer gas, peak current and time can be used to roughly sort lines by their upper energy level in the analysis of complex atomic spectra.