Measurement of metastable and resonance level densities in rare-gas plasmas by optical emission spectroscopy

Abstract

Excitation and ionization of atoms out of the 4 energy levels of the excited np 5 (n + 1)s configuration of rare gases play an important role in many low temperature rare-gas plasmas. We compare two optical methods for measuring the number densities of atoms in these excited levels in an inductively coupled plasma under a variety of operating conditions (600 W, 1-25 mTorr). The first method is a standard white light absorption technique, whereas the second method exploits changes in the effective branching fractions of np 5 (n + 1)p → np 5 (n + 1)s emissions brought about by radiation trapping of atoms in np 5 (n + 1)s levels. The branching fraction method was found to produce results that agree well with the direct white light absorption method for both argon and neon plasmas using little more than a low-resolution spectrum of the plasma glow.

Comparison of surface vacuum ultraviolet emissions with resonance level number densities. II. Rare-gas plasmas and Ar-molecular gas mixtures

“…A brief description of the two methods follows; a longer description can be found in Ref. 1. A comparison of the results obtained with the two techniques can be found in the Appendix.…”

“…1,30 Areas of the observed absorption dips observed on multiple lines were converted to number densities using standard techniques. 31 To provide some redundancy, between two and six lines were used (depending upon the gas) for each resonance level to determine the number densities.…”

“…1s y lines using the radiation trapping induced changes to the branching fractions (BF) of lines out of a common 2p x upper level to measure the density of atoms in the 1s y lower levels. 1,32,33 Details on the spectrometers and transitions used for each gas are included in the Appendix.…”

Measurements of sputtered neutrals and ions and investigation of their roles on the plasma properties during rf magnetron sputtering of Zn and ZnO targets

“…This difference could result from radiation trapping of the Ar 2p 1 -to-1s 2 (Paschen notation) transition at 750.4 nm since Ar is the main plasma gas in the present experiments. We have estimated the escape factor of this Ar I emission line using the empirical formula reported by Boffard et al 36 for Doppler-broadened lines. For a gas temperature of 300 K, an absorption length of 32 cm, and an estimated number density of Ar 1s 2 of $10 8 cm À3 (see Ref.…”

Application of the escape factor method for determination of excited states densities in a low‐pressure argon radio‐frequency discharge

“…In that paper, the column number densities of the four lowest excited states were obtained, but there was no comparison done with other independent method. It was done in the work [16] for the case of pressure dependence in argon and neon ICP discharges. Our modification of the method differences more in form, rather then in fundamental content.…”