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

Abstract

Key words Escape factor, rf discharge in argon, metastable state, emission spectroscopy, TDLAS.Reabsorption of the emitted light in the plasma volume has recently been used for density measurements of the lower level of optical transition by interpretation of emission spectra employing the escape factor concept. Following this idea, we apply this method to a radio-frequency argon discharge. By revising the theoretical background, the impact of different assumptions on excited species spatial distributions is investigated. Comparing with 1s5 and 1s4 concentrations obtained with laser absorption spectroscopy, the range of applicability of those assumptions is analyzed at different discharge parameters.

Argon metastable and resonant level densities in Ar and Ar/Cl2 discharges used for the processing of bulk niobium

“…In the branching fraction method, the irradiances from a pair of 2p!1s transitions with the same upper level are divided to eliminate the density of the 2p state and the geometric factor. This leads to 12,17,22…”

“…A significant goal of this work is to explore the spectroscopic technique now known as the optical emission spectroscopybranching fraction method (OES-BFM). 12,17,22,23,32 This technique uses the intensities of partially self-absorbed spectral emission lines from 2p!1s transitions to determine the amount of reabsorbed photons (the photon escape factor). This optical emission spectroscopy technique is essentially nonintrusive and dependent on the distribution of the lower state density of the transition.…”

“…2p. [22][23][24][25] The Doppler broadened line profile allows one to evaluate the kinetic gas temperature of atoms in the particular 1s state. This value is necessary in all evaluations of the absorption coefficients for all transitions involved in the two techniques.…”

Understanding Microwave Surface‐Wave Sustained Plasmas at Intermediate Pressure by 2D Modeling and Experiments

“…The absolute population of the different atomic levels in the 1s group (formed by two metastable 1 s 5 and 1 s 3 and two resonant levels 1 s 2 and 1 s 4 ) was determined using so‐called passive spectroscopy , based on the study of the self‐ absorption of photons generated in 2 p → 1 s transitions. The self‐absorption method has been extensively studied and widely used in various spectroscopic measurements . This method is suitable for absolute density measurements if the population of the lower state of a particular optical transition is high enough to provide a traceable optical thickness.…”

“…The self-absorption method has been extensively studied [76,77] and widely used in various spectroscopic measurements. [78][79][80] This method is suitable for absolute density measurements if the population of the lower state of a particular optical transition is high enough to provide a traceable optical thickness. In this case, the reabsorption of emission lines is taken into account via the concept of an escape factor, [79] which turns the emission transitions dependent on the metastable and resonant absolute population.…”