Pressure broadening of 772.376 and 772.421 nm argon lines and kinetics of argon metastable atoms

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Tunable diode laser absorption spectroscopy was used to record the space-and time-resolved number density of argon metastable atoms, Ar(1s3) (Paschen notation), in plane-to-plane dielectric barrier discharges operated in a Penning Ar-NH3 mixture at atmospheric pressure. In both low-frequency (LF 650 V, 50 kHz) discharges and dual LF-radiofrequency (RF 190 V, 5 MHz) discharges operated in α-γ mode, the density of Ar(1s3) revealed a single peak per half-period of the LF voltage, with rise and decay times in the sub-microsecond time scale. These results were compared to the predictions of a 1D fluid model based on continuity and momentum equations for electrons, argon ions (Ar+ and Ar2 +) and excited argon 1s atoms as well electron energy balance equation. Using the scheme commonly reported for Ar-based dielectric barrier discharges in the homogeneous regime, the Ar metastable kinetics exhibited much slower rise and decay times than the ones seen in the experiments. The model was thus refined by considering the fast creation of Ar2 * excimers through 3-body reactions involving Ar(1s) atoms and the rapid loss of Ar2 *by vacuum ultraviolet light emission. In optically thin media for such photons, they can readily reach the dielectric barriers of the DBD electrodes and induce secondary electron emission. It is shown that Ar2 * and photoemission play a significant role not only on the Ar metastable kinetics, but also on the dominant ionization pathways and possible α-γ transition in dual frequency RF-LF discharges.

Section: Measurement Of Argon Metastable Atomsmentioning

confidence: 99%

Section: Measurement Of Argon Metastable Atomsmentioning

confidence: 99%

Role of excimer formation and induced photoemission on the Ar metastable kinetics in atmospheric pressure Ar–NH₃ dielectric barrier discharges

Robert¹,

Hagelaar²,

Sadeghi³

et al. 2022

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“…Due to the closeness of the Ar transitions 772.38 nm (2p 7 ← 1s 5 ) and 772.42 nm (2p 2 ← 1s 3 ), and their pressure broadening at 760 Torr, the laser beam can be absorbed by both Ar(1s 5 ) and Ar(1s 3 ) metastable atoms (Paschen notations are used, corresponding to 4s[3/2] 2 and 4s[1/2] 0 metastable states in Racah notation) [48]. However, as the oscillator strength of the 2p 2 ← 1s 3 transition is more than an order of magnitude larger than the one of the 2p 7 ← 1s 5 transition [48], by setting the laser wavelength at 772.435 nm, which is the peak position of the pressure-shifted 2p 2 ← 1s 3 line [49], the absorption signal represents the density of Ar(1s 3 ) atoms [47,49]. The time-resolved number density of Ar(1s 3 ) atoms can be deduced from the time-resolved absorption coefficient at 772.435 nm, using relations reported in [49][50][51].…”

Section: Tunable Diode Laser Absorption Spectroscopymentioning

confidence: 99%

“…However, as the oscillator strength of the 2p 2 ← 1s 3 transition is more than an order of magnitude larger than the one of the 2p 7 ← 1s 5 transition [48], by setting the laser wavelength at 772.435 nm, which is the peak position of the pressure-shifted 2p 2 ← 1s 3 line [49], the absorption signal represents the density of Ar(1s 3 ) atoms [47,49]. The time-resolved number density of Ar(1s 3 ) atoms can be deduced from the time-resolved absorption coefficient at 772.435 nm, using relations reported in [49][50][51]. Here, the about 500 µm diameter of the laser beam limits the spatial resolution within the gap but allows to estimate the Ar(1s 3 ) atoms density either in the plasma bulk (middle distance from the top and bottom electrodes) or in a zone close to the top electrode, including the sheath edge.…”

Section: Tunable Diode Laser Absorption Spectroscopymentioning

confidence: 99%

Influence of the RF voltage amplitude on the space- and time-resolved properties of RF–LF dielectric barrier discharges in α–γ mode

Robert,

Sadeghi,

Hagelaar

et al. 2024

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This work reports the results of an experimental and modelling study on dual-frequency Ar-NH3 dielectric barrier discharges (DBD) exhibiting the α – γ transition. A combination of space- and time-resolved optical absorption and emission spectroscopy is used to record spatio-temporal mappings of the Ar metastable number density, Ar 750.4 nm line emission intensity, and electron-Ar Bremsstrahlung continuum emission intensity. With the increase of the RF voltage amplitude in a 50 kHz-5 MHz DBD, maximum populations of Ar excited species (1s and 2p states, linked to the population of high-energy electrons) observed in the γ mode decrease and appear earlier in the low-frequency cycle. On the other hand, the density of the bulk electrons, monitored from the continuum emission intensity, increases, with a more prominent rise in the RF-α mode than in the γ regime. Such behaviors are consistent with the predictions of 1D fluid model and results from a decrease of the gas voltage required for self-maintenance of the cathode sheath in the γ breakdown.

“…The 1s 5 argon metastable density and the gas temperature in the plasma are measured by TDLAS [82][83][84][85][86]. The density and the temperature of the Ar 1s 5 atoms are obtained from the measured absorption profile of the Ar 1s 5 → Ar 2p 6 transition at λ = 772.376 nm.…”

Section: Tdlas Setupmentioning

confidence: 99%

Metastable argon atom kinetics in a low-pressure capacitively coupled radio frequency discharge

Hartmann

Korolov

Schulenberg

et al. 2023

The kinetics of excited atoms in a low-pressure argon capacitively coupled plasma source are investigated by an extended Particle-in-Cell / Monte Carlo Collisions simulation code coupled with a Diffusion-Reaction-Radiation code which considers a large number of excited states of Ar atoms. The spatial density distribution of Ar atoms in the 1s$_5$ state within the electrode gap and the gas temperature are also determined experimentally using Tunable Diode Laser Absorption Spectroscopy. Processes involving the excited states, especially the four lower-lying 1s states are found to have significant effects on the ionization balance of the discharge. The level of agreement achieved between the computational and experimental results indicate that the discharge model is reasonably accurate and the computations based on this model allow the identification of the populating and de-populating processes of the excited states.