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

Wubs, J. R.; Invernizzi, L.; Gazeli, K.; Macherius, U.; Lü, X.; Schrottke, L.; Lombardi, G.; Weltmann, K.-D.; van Helden, J. H.

doi:10.1063/5.0160303

Cited by 7 publications

(11 citation statements)

References 37 publications

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“…O obtained in this work is similar to the data obtained in [13] and differs markedly from the ratio used in [27] were it was suggested, following [25,26] that the ratio should be reduced by a factor slightly greater than 2. The question of how the ratio of cross sections relates to the absolute value of the cross-section of the two-photon excitation of Xe measured in [25,26] remains open.…”

Section: Discussionsupporting

confidence: 83%

“…The ratio of the cross-sections, based on the measurements [25,26] and providing almost two times smaller atomic oxygen density, was recently used [27] to compare O-TALIF with THz absorption spectroscopy on the same capacitively coupled radio frequency oxygen discharge. Similar behaviour of the atomic oxygen density was observed for both techniques when varying the applied power (20-100 W) and the gas pressure (0.7-1.3 mbar).…”

Section: On Recent Measurements Of Cross-sections For Xementioning

confidence: 99%

“…in equation(27). Uncertainty δα/α was estimated by the error of Abel transform (radial profile) of N 2 SPS emission, δn O /n O and δn Xe /n Xe were taken from the accuracy of the flow rate controller and the pressure sensor, δτ Xe 0 /τ Xe 0 and δτ O 0 /τ O 0 were measured in[13].…”

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confidence: 99%

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Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications

Shu,

Popov,

Starikovskaia

2024

Plasma Sources Sci. Technol.

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The paper presents a calibration of the ratio of two-photon absorption cross sections, $\sigma^{(2)}_{Xe}/ \sigma^{(2)}_O$, necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100\% dissociation of molecular oxygen, and so with a known “reference” density of O-atom [O]$_{ref}$=2$\cdot$[O$_2$] was suggested. This is a nanosecond capillary discharge in N$_2$: O$_2$ mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Td and specific deposited energy of about 1 eV/molecule. Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2~ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O$_2$ dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ``reference'' density of oxygen atoms [O]$_{ref}$, the ratio of the two-photon absorption cross-sections $\sigma^{(2)}_{Xe}/ \sigma^{(2)}_O$ was determined.

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Section: Discussionsupporting

confidence: 83%

Section: On Recent Measurements Of Cross-sections For Xementioning

confidence: 99%

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Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications

Shu,

Popov,

Starikovskaia

2024

Plasma Sources Sci. Technol.

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“…In particular, the detection of fine structure transitions in atoms is of high interest, as this could provide a means of developing absolute detection methods for atoms based on direct absorption spectroscopy. Recent examples of this are the detection of atomic oxygen by heterodyne spectroscopy in astronomy and atmospheric research [12][13][14] and the determination of the absolute densities of oxygen atoms in a plasma reactor [15][16][17]. There have been a few reports on the application of THz QCLs for absorption spectroscopy in the gas phase as well [18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

“…In addition to the requirement of cryogenic cooling, they typically have a limited bandwidth in the order of up to a few hundred Hz for the 3 dB roll-off frequency, which significantly reduces the laser tuning frequencies that can be applied and thus leads to longer measurement times when recording an absorption spectrum. For example, in previous work [15,16], laser tuning frequencies of 10 Hz or 11 Hz had to be used to avoid any asymmetric deformation of the observed absorption features, which, in turn, also limited the spectral range that could be probed.…”

Section: Introductionmentioning

confidence: 99%

Performance of a High-Speed Pyroelectric Receiver as Cryogen-Free Detector for Terahertz Absorption Spectroscopy Measurements

Wubs,

Macherius,

Lü

et al. 2024

Applied Sciences

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The application of terahertz (THz) radiation in scientific research as well as in applied and commercial technology has expanded rapidly in recent years. One example is the progress in high-resolution THz spectroscopy based on quantum cascade lasers, which has enabled new observations in astronomy, atmospheric research, and plasma diagnostics. However, the lack of easy-to-use and miniaturised detectors has hampered the development of compact THz spectroscopy systems out of the laboratory environment. In this paper, we introduce a new high-speed pyroelectric receiver as a cryogen-free detector for THz absorption spectroscopy. Its performance is characterised by absorption spectroscopy measurements on a reference gas cell (RGC) with ammonia using a tunable THz quantum cascade laser at approximately 4.75 THz as the light source. It is shown that the receiver can record spectra up to 281 Hz without any artefacts to the observed spectral absorption profile, and the results reproduce the known pressure of ammonia in the RGC. This demonstrates that the pyroelectric receiver can be reliably used as an alternative to helium-cooled bolometers for absorption spectroscopy measurements in the THz range, with its main advantages being the high bandwidth, compactness, relatively low cost, and room-temperature operation. Its simplicity and high sensitivity make this receiver a key component for compact THz spectroscopy systems.

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Measurement of atomic oxygen densities using TALIF on a dielectric barrier discharge: insights into the volume above a micro cavity plasma array

Steuer,

Bentz,

Youngman

et al. 2024

Plasma Sources Sci. Technol.

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Dielectric barrier discharges, particularly micro cavity plasma arrays, offer significant potential for plasma-catalytic research due to their ability to ignite plasma in direct contact with a catalytic surface, enabling the observation of plasma-surface interactions. A key factor in their application is the generation of reactive species, such as atomic oxygen, within the cavities. These species can interact with both, the surface (e.g., for activation or cleaning) and the gas being treated (e.g., for oxidation). Given the central role of oxygen atoms in plasma catalysis and their use as a model for more complex species, this work investigates the transport of these atoms out of the cavities. Two-photon absorption laser induced fluorescence (TALIF) spectroscopy with picosecond resolution is performed in the volume above the cavities. The results are compared with a basic diffusion model. The reactor operates with a He/O2 mixture at a flow rate of 1 slm and atmospheric pressure. Densities of up to 1016cm-3 are measured near the surface. Time-dependent measurements show that, at a distance of 350 µm from the surface, a density equilibrium is reached within less than 3 ms of reactor operation. Decay times due to ozone formation after the reactor is turned off are on a similar scale. Spatially resolved measurements show that the oxygen density decreases exponentially from the surface but remains detectable up to approximately 1 mm above the surface, indicating significant application potential. Variations in the O2 admixture show a density maximum at 0.4%, confirming previous helium state enhanced actinometry measurements within the cavities.

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

Cited by 7 publications

References 37 publications

Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications

Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications

Performance of a High-Speed Pyroelectric Receiver as Cryogen-Free Detector for Terahertz Absorption Spectroscopy Measurements

Measurement of atomic oxygen densities using TALIF on a dielectric barrier discharge: insights into the volume above a micro cavity plasma array

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