Abstract

Spectral profiles of Au i, Ar i, and Ar ii lines obtained with a scanning Fabry–Perot spectrometer from a low-current, 3.2-mm-diam Au hollow-cathode discharge in ~6 torr of Ar are fitted with Voigt functions to determine the apparent lorentzian half-widths, ΔL_s, and apparent Doppler temperatures, T_s, as functions of the discharge current. T_s values of the Au i 4792-Å line are approximately equal to those of the Ar i lines, whereas for the Au i 3123-Å line, the T_s values are much greater. Arguments are presented to show that these high T_s values result from the high initial ejection energy of the sputtered atoms and the short lifetime of the upper state. Typically, T_s = 1010, 1180, and 1760 K for the Ar i 4511, Au i 4792, and Au i 3123-Å lines, respectively. The T_s values of the Ar ii doublet-state lines equal those of the Ar i lines, whereas for the Ar ii quartet-state lines, the T_s values are significantly lower. The ΔL_s values of the Ar i lines, whose transitions terminate on resonance states, are predicted by resonance-broadening theory. The ΔL_s values of the Ar ii lines range from 0.010 to 0.031 cm⁻¹ and far exceed the calculated resonance- and Stark-broadening terms. A proposed model of the Ar ii spectral-line profile consists of a superposition of two pure gaussian distributions, which represent one group of high-energy ions accelerated by axial electric fields in an electrical double layer (DL) at the end of the cathode, and a second group in equilibrium with Ar atoms. The sum closely approximates a Voigt function whose analysis yields apparent values, ΔL_c and T_c, which equal the corresponding observed quantities. The ΔL_s values are found to vary with discharge conditions, presumably depending upon the completion of the DL formation.

© 1970 Optical Society of America

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