R.O. Jung

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

Excitation and ionization of atoms out of the 4 energy levels of the excited np5(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 np5(n + 1)p → np5(n + 1)s emissions brought about by radiation trapping of atoms in np5(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.

Optical emission measurements of electron energy distributions in low-pressure argon inductively coupled plasmas

Optical modeling of emissions from low-temperature plasmas provides a non-invasive technique to measure the electron energy distribution function (EEDF) of the plasma. While many models assume the EEDF has a Maxwell?Boltzmann distribution, the EEDFs of numerous plasma systems deviate significantly from the Maxwellian form. In this paper, we present an optical emission model for the Ar(3p54p ? 3p54s) emission array which is capable of capturing details of non-Maxwellian distributions. Our model combines previously measured electron-impact excitation cross sections with Ar(3p54s) number density measurements and emission spectra. The model also includes corrections for radiation trapping of the Ar(3p54p ? 3p54s) emission lines. Results obtained with this optical technique are compared with corresponding Langmuir probe measurements of the EEDF for Ar and Ar/N2 inductively coupled plasma systems operating under a wide variety of source conditions (1?25?mTorr, 20?1000?W, %N2 admixture). Both the optical emission method and probe measurements indicate the EEDF shapes are Maxwellian for low electron energies, but with depleted high energy tails.

Electron-impact excitation cross sections into Ne(2p53p) levels for plasma applications

One requirement for plasma spectroscopy analysis and modeling of neon discharges is a set of electron-impact excitation cross sections covering excitation from both the 2p6 ground state and from the four 2p53s levels. We present experimental measurements for excitation cross sections into four J = 1 levels of the 2p53p configuration from the J = 0 and J = 2 2p53s metastable levels. A complete set of cross sections into all ten levels of the 2p53p configuration (2px in Paschen’s notation) from the ground state, the two metastable levels and the two resonance levels of the 2p53s configuration (1sy in Paschen’s notation) are compiled in convenient form. The resonance cross sections are obtained from an empirical scaling relationship between the measured metastable excitation cross sections and the corresponding optical oscillator strengths.