Optical emission and absorption spectroscopy of argon 2p-1s transitions (Paschen notation) combined with collisional-radiative (CR) modeling of argon 2p states are developed and used to determine the neutral gas temperature, the Ar 1s number density, and the electron temperature along a microwave argon plasma column at atmospheric pressure. The CR model, designed specifically for atmospheric-pressure and optically thick plasma conditions, is fully detailed and validated by comparing the relative line emission intensities of argon 2p-to-1s transitions measured experimentally with the ones predicted by the CR model using the electron temperature as the only adjustable parameter. Subsequently, the neutral gas temperature (∼1300–1600 K; obtained from the broadening of argon 2p₂-1s₂ and 2p₃-1s₂ emission lines), the Ar 1s₅ number density (1–2 $\times$ 10¹⁸ m⁻³; obtained from absorption spectroscopy of the argon 2p₉-1s₅ transition using a tunable laser diode), and the electron temperature (∼1.4 eV; obtained from the comparison between the measured and simulated 2p-to-1s emission line intensities) are reported as a function of the axial distance along the microwave plasma column. The values and behaviors reveal a good agreement with those reported in previous experimental and modeling studies.

A combination of optical emission spectroscopy and collisional-radiative modelling is used to determine the time-resolved electron temperature (assuming Maxwellian electron energy distribution function) and number density of Ar 1s states in atmospheric pressure Ar-based dielectric barrier discharges in presence of either NH ₃ or ethyl lactate. In both cases, T _e values were higher early in the discharge cycle (around 0.8 eV), decreased down to about 0.35 eV with the rise of the discharge current, and then remained fairly constant during discharge extinction. The opposite behaviour was observed for Ar 1s states, with cycle-averaged values in the 10 ¹⁷ m ⁻³ range. Based on these findings, a link was established between the discharge ionization kinetics (and thus the electron temperature) and the number density of Ar 1s state.

A combination of optical emission and absorption spectroscopy of argon 2 p –1 s transitions (Paschen notation) combined with collisional-radiative (CR) modelling of argon 2 p states was used to characterize microwave argon plasmas at atmospheric pressure in presence of N ₂ , O ₂ , and H ₂ admixtures. In particular, the neutral gas temperature (obtained from the broadening of argon 2 p ₂ –1 s ₂ and 2 p ₃ –1 s ₂ emission lines), the number density of argon 1 s ₅ atoms (obtained from absorption spectroscopy of the argon 2 p ₉ –1 s ₅ transition using a tunable laser diode), the electron temperature (obtained from the comparison between measured and simulated argon 2 p -to-1 s relative line emission intensities), and the electron density (obtained from the Stark broadening of the H _β line and argon relative line emission intensities) were recorded as a function of the axial distance along the microwave plasma column. The results show that, for a given position in the plasma and a higher amount of admixture in the nominally pure argon plasma, the neutral gas temperature increases and the electron number density decreases, while the electron temperature and the population of argon metastable atoms first decreases and then increases at higher concentrations. With such information, a detailed analysis of the electron power balance was performed. It is found that less than 1% of the admixture in the argon plasma already absorbed more than 80% of the microwave power. Part of this energy is used for neutral gas heating, mostly through electron-impact excitation of rotational levels.

The spatially-resolved electron temperature, rotational temperature, and number density of the two metastable Ar $1s$ levels were investigated in a miniature RF Ar glow discharge jet at atmospheric pressure. The $1s$ level population densities were determined from optical absorption spectroscopy (OAS) measurements assuming a Voigt profile for the plasma emission and a Gaussian profile for the lamp emission. As for the electron temperature, it was deduced from the comparison of the measured Ar $2p_i\to 1s_j$ emission lines with those simulated using a collisional-radiative model. The Ar $1s$ level population higher than 10 ${}^{18}$ m ${}^{-3}$ and electron temperature around 2.5 eV were obtained close to the nozzle exit. In addition, both values decreased steadily along the discharge axis. Rotational temperatures determined from OH(A) and N ${}_2$ (C) optical emission featured a large difference with the gas temperature found from a thermocouple; a feature ascribed to the population of emitting OH and N ${}_2$ states by energy transfer reactions involving the Ar $1s$ levels.

This work examines the rotational–translational equilibrium in non-thermal, argon-based plasmas at atmospheric pressure. In particular, rotational temperatures ( T _rot ) and neutral gas temperatures ( T _g ) are compared along the axis of plasma columns sustained by either radiofrequency (RF) or microwave (MW) electromagnetic fields. Water vapours or N ₂ admixtures are added to the high-purity argon plasmas to record the rotational temperatures from the emission spectra of either the OH(A ² Σ ⁺ − X ² Π _i ) or the N ₂ ⁺ (B ² Σ _u ⁺ − X ² Σ _g ⁺ ) rovibrational systems. T _g values are also deduced from the line broadening of selected Ar emission lines using an hyperfine spectrometer. In the MW Ar/H ₂ O plasma, T _g decreases from ∼2100 K close to the wave launcher to ∼1600 K near the end of the plasma column, while T _rot is mostly constant in the 1500 K range. In presence of N ₂ admixtures instead of water vapours, T _g is higher by about 300 K (from ∼2400 K to ∼1900 K), while T _rot decreases from ∼3200 K to ∼2750 K along the plasma column. A discrepancy between T _g and T _rot is also observed in the much colder RF plasmas with T _g ∼ 400 K and T _rot ∼ 515 K. Such departure from the rotational–translational equilibrium in both plasmas is ascribed to the influence of electrons competing with neutrals to impose their own temperature on the distribution of rotational levels of both ground and excited states.

The need to ensuring the “see‐through” property of transparent materials when exposed to sudden temperature changes or very humid conditions has encouraged the development of antifogging strategies, such as the deposition of (super)hydrophilic coatings. However, despite the effectiveness of these coatings in combating the effects of fogging, most of the coating techniques explored to date are typically time‐consuming and environment‐unfriendly. Bearing this in mind, we demonstrate that the application of dielectric barrier discharges operated at atmospheric pressure proves to be successful in preparing antifogging coatings on glass samples from 1,3,5,7‐tetramethylcyclotetrasiloxane (TMCTS) and nitrous oxide (N₂O). The antifogging performance of the coatings was found to be governed by the [N₂O]/[TMCTS] ratio and not by the [N₂O] + [TMCTS] sum. Coatings prepared under a [N₂O]/[TMCTS] = 30 were superhydrophilic (water contact angles ≈ 5°–10°) due to surface silanol groups and endowed glass samples with a superior antifogging property, as revealed by the ASTM F 659‐06 test. In contrast, because of the lesser hydrophilicity (water contact angles ≈ 60°), coatings prepared under a [N₂O]/[TMCTS] = 10 did not endow glass samples with antifogging property. Regardless of the deposition conditions, the plasma‐deposited coatings displayed crack‐free smooth surfaces (R_rms = 2−4 nm).