Validation of THz absorption spectroscopy by a comparison with ps-TALIF measurements of atomic oxygen densities

Terahertz (THz) absorption spectroscopy has recently been developed as a diagnostic technique for measuring absolute ground-state atomic oxygen densities in plasmas. To demonstrate the validity of this approach, we present in this Letter a benchmark against a more established method. Atomic oxygen d...

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Bibliographic Details
Published in:Applied physics letters 2023-08, Vol.123 (8)
Main Authors: Wubs, J. R., Invernizzi, L., Gazeli, K., Macherius, U., Lü, X., Schrottke, L., Lombardi, G., Weltmann, K.-D., van Helden, J. H.
Format: Article
Language:English
Subjects:
Absorption spectroscopy
Applied physics
Atomic oxygen
Electrons
Gas pressure
Instrumentation and Detectors
Laser induced fluorescence
Photon absorption
Physics
Plasma Physics
Plasmas (physics)
Spectroscopic analysis
Spectrum analysis
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Summary:Terahertz (THz) absorption spectroscopy has recently been developed as a diagnostic technique for measuring absolute ground-state atomic oxygen densities in plasmas. To demonstrate the validity of this approach, we present in this Letter a benchmark against a more established method. Atomic oxygen densities were measured with THz absorption spectroscopy and compared to those obtained from picosecond (ps) two-photon absorption laser induced fluorescence (TALIF) measurements on the same capacitively coupled radio frequency oxygen discharge. Similar changes in the atomic oxygen density were observed with both diagnostics when varying the applied power (20–100 W) and the gas pressure (0.7–1.3 mbar). Quantitatively, the results are in good agreement as well, especially when considering the total margin of error of the two diagnostics. For example, for a gas pressure of 1.3 mbar and an applied power of 30 W, atomic oxygen densities measured with THz absorption spectroscopy and TALIF were ( 7.0   ±   1.7 ) × 10 14 cm−3 and ( 5.3   ±   3.2 ) × 10 14 cm−3, respectively. This shows that THz absorption spectroscopy is an accurate technique that can be reliably used for real-world applications to determine atomic oxygen densities in plasmas.
ISSN:0003-6951
1077-3118
DOI:10.1063/5.0160303