State enhanced actinometry in the COST microplasma jet

Abstract

A new actinometry approach, helium state enhanced actinometry (SEA), is presented. This diagnostics uses the emission of the atomic states O(3p3P) (λ=844.6 nm), Ar(2p1) (λ=750.4 nm) and He(33S) (λ=706.5 nm) and allows the atomic oxygen density and the mean electron energy to be determined simultaneously from the spectral line intensity ratios. Here, the atomic states are selected in a way that they cover a wide range of the electron energy distribution function (EEDF). The method is compared to the classical actinometry approach and energy resolved actinometry (ERA) based on measurements on the COST microplasma jet. In addition, a benchmark against two-photon absorption laser induced fluorescence (TALIF) measurements is performed. Both atomic oxygen densities and mean electron energies are in good agreement with the literature. Furthermore, SEA offers a number of advantages over known approaches. Firstly, the experimental complexity is significantly reduced by using time-integrated spectra instead of phase-resolved measurements, as used in the original ERA approach. Secondly, the precision of the energy measurement can be significantly improved by the use of the helium state. In addition, known uncertainties e.g. due to excitation of oxygen excited levels via metastable oxygen states can be reduced.

Terahertz absorption spectroscopy for measuring atomic oxygen densities in plasmas

“…With this wavenumber axis, the fine structure transition of atomic oxygen is located at a position that matches within the margin of error with the transition wavenumber of 158.268 741 cm −1 given in literature (uncertainty: ≈ 0.000 01 cm −1 ) [20]. In addition, a second ammonia transition is visible in the spectrum, namely, the aR(7, 2)-transition of 14 NH 3 . It has a reported transition wavenumber of 158.294 830 cm −1 , but with a relatively large uncertainty (in the range between 0.001 and 0.01 cm −1 ) [38].…”

“…Noise and fluctuations caused I 0 to be insufficiently reproducible for it to be measured separately; therefore, it was determined by fitting a second order polynomial function to I while excluding the part affected by absorption from the fit. The resulting absorption spectrum, recorded with a laser tuning window of 120 mA and zoomed in on the sR(7, 3)-transition of 14 NH 3 at 158.214 792 cm −1 , is given by the black curve in figure 4.…”

“…296 K), ∆ν D equals 4.7 × 10 −4 cm −1 . To determine the instrumental contribution to the broadening of spectral lineshapes, the sR(7, 3)-transition of 14 NH 3 at 158.214 792 cm −1 was measured at a pressure of approximately 0.01 mbar using a RGC with a length of 3 cm. A Gaussian function was fitted to the recorded spectral profile, as shown in figure 5.…”

“…In addition, TALIF measurements are indirect, meaning that a calibration procedure is required to obtain absolute atomic oxygen densities, which involves a comparison between two-photon excitation cross sections for oxygen and xenon [10]. A second technique that has been used in the past to measure atomic oxygen densities is actinometry [11][12][13][14]. This is a relatively simple method based on optical emission spectroscopy, using e.g.…”

Spatio-temporal dynamics of electrons and helium metastables in uniform dielectric barrier discharges formed in He/N2

“…In this context, under atmospheric pressure conditions, the combination of optical emission spectroscopy (OES) and numerical simulations has been presented as a versatile diagnostic tool to obtain information about plasma conditions, such as E/N and n e [10][11][12] or reactive species densities [13][14][15] at sufficient temporal and spatial resolution. While there are a variety of methods to combine experiment and simulation for this purpose, typical schemes involve the calculation of electron energy distribution functions using a numerical solution of the Boltzmann equation at variable reduced electric fields.…”