# Optical Emission Spectroscopy as a Diagnostic Tool for Characterization of Atmospheric Plasma Jets
## 1 Introduction
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**REF** & **Gas Composition** & **APPJ Configuration** & **Findings by OES Diagnostics** \\ \hline \multirow{4}{*}{[13]} & Ar/TEOS (tetraethyl orthosilicate) & AlmaJET, single electrode corona jet, AC power supply, 12 kHz, 12 kV implatlute, power 11.5 W, Ar flow 2 km, 17 ppm TEOS & Besides peaks characteristic for Ar plasma with the presence of water vapor, the addition of TEOS resulted in the appearance of additional excited species: CH, CN, and C\({}_{2}\) bands. \(T_{\text{rot}}\) of OH(A), N\({}_{2}\)(C), and CH(A) were determined using two different simulation software. \(T_{\text{rot}}\) calculated from OH was much lower (410 K) than \(T_{\text{rot}}\) calculated from N\({}_{2}\) (550 K) and CH (590 K). The length of the plasma jet was decreasing with increasing water content. At very high water content, the plasma was unstable. In pure Ar plasma, N\({}_{2}\) dominated in OES spectra measured 2 mm from the nozzle. With the addition of water vapor, N\({}_{2}\) diminished, and OH became dominant. T\({}_{\text{rot}}\) was determined, and it increased with water addition. Besides Ar, molecular N\({}_{2}\), atomic O and OH were observed in pure Ar plasma. The addition of CO\({}_{2}\) caused a decrease in emission lines and the disappearance of oxygen, whereas OH and N\({}_{2}\) were still observed. Additionally, the CO Angstrom band was observed in Ar/CO\({}_{2}\) mixture. OES was measured 15 mm from the ground electrode. OH and lines of Ar were found. T\({}_{\text{rot}}\) was determined, and it was increasing with the increase in the water content. The addition of water to Ar caused the decrease in all atomic line intensities. The emission of OH radicals was not linearly dependent on the water content, but it had a maximum at 350 ppm. The electron temperature was measured (0.4 eV). The plume temperature was also measured versus voltage and flow rate. Depending on the frequency and gas flow, it was in the range 25-40 \({}^{\circ}\)C. Ar, as well as atomic O, OH, and N\({}_{2}\) peaks, were found in Ar plasma. OH peak was much stronger than O line even if O\({}_{2}\) was added to Ar. The origin of water was the desorption of water molecules from the quartz discharge tube. Besides Ar lines, significant OH radiation was observed as well as N\({}_{2}\) lines and O-atom line. The increase in water content caused a decrease in all atomic lines. The addition of water also caused an increase in the gas temperature from 620 (pure Ar) to 1130 K (0.76\(\%\) H\({}_{2}\)O). OES profiles were measured along with the jet every 5 mm up to a distance of 35 mm. The OH concentration was maximal at the minimum addition of water to the feed gas (0.05\(\%\)).  
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Table 1: T Summary of characterization of APPJ by OES. * [34] He + H\({}_{2}\)O & AC power supply, 18 kV, 15 kHz, He flow 20 L/min, H\({}_{2}\)O flow 3 mL/min & DBD type APT, AC power supply, 5 kV, 50 kHz, He flow: 2-4 slm, Ar flow: 1-3.5 slm & 2% H\({}_{2}\)O in Ar/Air mixture, Ar flow 3 lpm, air flow: 3-15 lpm, voltage 4-7 kV, 250 Hz square wave power source & DBD plasma jet, pulsed DC power supply, 10 kHz, duty cycle 20%, peak-to-peak voltage 2-3.2 kV, min. power & 5 W, He flow 2.5-5.5 slm & DBD-type APTJ, AC power supply, 60 kHz, peak to peak voltage 6-14 kV, 18 W, gas flow 3 slm, 0.1-0.5% of O\({}_{2}\) & \\
* [32] Ar, He (with/o addition of CH\({}_{4}\) or C\({}_{2}\)H\({}_{2}\)) & 13.56 MHz, rms voltage & The collimating lens was positioned 140 mm from the end of the jet. The special construction of APPJ allowed the insertion of Ar(He)/CH\({}_{4}\) gas by a capillary tube into the main Ar/He flow, which prevents the mixing of the surrounding gas. In pure Ar plasma, the Ar and OH emission dominated. Additionally, in the Ar/CH\({}_{4}\) mixture, CH and C\({}_{2}\) bands were observed. In Ar/CH\({}_{4}\), CH was more dominant than C\({}_{2}\); whereas, in Ar/C\({}_{2}\)H\({}_{2}\), C\({}_{2}\) band was more intense.