Absolute calibration of atomic density measurements by laser-induced fluorescence spectroscopy with two-photon excitation

Niemi, Kari; Gathen, Volker Schulz-von der; Döbele, H. F.

doi:10.1088/0022-3727/34/15/312

Cited by 282 publications

(379 citation statements)

References 22 publications

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“…Similar to reaction (R 21 ), a mechanism has been proposed in [41] for the generation of O: However, because of air diffusion into the jet, the active species map has to follow a 'donut'-like distribution, with higher intensity on the edges, due to the profile of N 2 , H 2 O and O 2 densities in the afterglow. In fact, the 'donut'-like shape of the LIF OH distribution in the afterglow of a He pulsed discharge operated in ambient air has been observed recently in [42].…”

Section: Discussionmentioning

confidence: 95%

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Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Nikiforov

Britun

et al. 2014

Plasma Sources Sci. Technol.

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Treatment of samples with plasmas in biomedical applications often occurs in ambient air. Admixing air into the discharge region may severely affect the formation and destruction of the generated oxidative species. Little is known about the effects of air diffusion on the spatial distribution of OH radicals and O atoms in the afterglow of atmospheric-pressure plasma jets. In our work, these effects are investigated by performing and comparing measurements in ambient air with measurements in a controlled argon atmosphere without the admixture of air, for an argon plasma jet. The spatial distribution of OH is detected by means of laser-induced fluorescence diagnostics (LIF), whereas two-photon laser-induced fluorescence (TALIF) is used for the detection of atomic O. The spatially resolved OH LIF and O TALIF show that, due to the air admixture effects, the reactive species are only concentrated in the vicinity of the central streamline of the afterglow of the jet, with a characteristic discharge diameter of ∼1.5 mm. It is shown that air diffusion has a key role in the recombination loss mechanisms of OH radicals and atomic O especially in the far afterglow region, starting up to ∼4 mm from the nozzle outlet at a low water/oxygen concentration. Furthermore, air diffusion enhances OH and O production in the core of the plasma. The higher density of active species in the discharge in ambient air is likely due to a higher electron density and a more effective electron impact dissociation of H 2 O and O 2 caused by the increasing electrical field, when the discharge is operated in ambient air.

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Section: Discussionmentioning

confidence: 95%

“…The best fit between the measured and calculated values of the parameter τ gives the desired value of the air fraction. (II) For a known density and quenching rate [20][21][22][23][24] [21]. Data for collisional quenching of OH(A) and ro-vibrational dependent cross-sections can be found in [20,[22][23][24].…”

Section: Experimental Set-upmentioning

confidence: 99%

Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Nikiforov

Britun

et al. 2014

Plasma Sources Sci. Technol.

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“…In the quadratic regime and under equal excitation conditions, the ratio of the ͑temporally and spectrally integrated͒ fluorescence signals S X that are given by Eq. ͑1͒, where XϭKr or H, reduces to [27][28][29] …”

Section: B Two-photon Excitation Of Kryptonmentioning

confidence: 99%

“…This approach avoids the cumbersome generation of a known amount of atomic radicals from an independent source. The method has recently been demonstrated for the calibration of ground-state H densities 27 as well as of ground-state N densities 27,28 using a two-photon transition in krypton. The method has also been applied to calibrate the fluorescence yield of oxygen atoms via a two-photon transition in xenon.…”

Section: Introductionmentioning

confidence: 99%

“…The subsequent comparison between the two calibration methods enables a first validation of the previously reported excitation cross section data. 27 The two-photon LIF technique has been used to completely map the H density, temperature, and velocity ͑along two independent axes͒ in the ETP. A lot of effort has been spent to quantify the data and to assess its reliability.…”

Section: Introductionmentioning

confidence: 99%

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Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

Boogaarts

Mazouffre

Brinkman

et al. 2002

Review of Scientific Instruments

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We report on quantitative, spatially resolved density, temperature, and velocity measurements on ground-state atomic hydrogen in an expanding thermal Ar-H plasma using two-photon excitation laser-induced fluorescence ͑LIF͒. The method's diagnostic value for application in this plasma is assessed by identifying and evaluating the possibly disturbing factors on the interpretation of the LIF signal in terms of density, temperature, and velocity. In order to obtain quantitative density numbers, the LIF setup is calibrated for H measurements using two different methods. A commonly applied calibration method, in which the LIF signal from a, by titration, known amount of H generated by a flow-tube reactor is used as a reference, is compared to a rather new calibration method, in which the H density in the plasma jet is derived from a measurement of the two-photon LIF signal generated from krypton at a well-known pressure, using a known Kr to H detection sensitivity ratio. The two methods yield nearly the same result, which validates the new H density calibration. Gauging the new ''rare gas method'' by the ''flow-tube reactor method,'' we find a krypton to hydrogen two-photon excitation cross section ratio Kr ͑2͒ / H (2) of 0.56, close to the reported value of 0.62. Since the H density calibration via two-photon LIF of krypton is experimentally far more easy than the one using a flow-tube reactor, it is foreseen that the ''rare gas method'' will become the method of choice in two-photon LIF experiments. The current two-photon LIF detection limit for H in the Ar-H plasma jet is 10 15 m Ϫ3 . The accuracy of the density measurements depends on the accuracy of the calibration, which is currently limited to 33%. The reproducibility depends on the signal-to-noise ͑S/N͒ ratio in the LIF measurements and is orders of magnitude better. The accuracy in the temperature determination also depends on the S/N ratio of the LIF signal and on the ratio between the Doppler-width of the transition and the linewidth of the excitation laser. Due to the small H mass, the current linewidth of the UV laser radiation is never the accuracy limiting factor in the H temperature determination, even not at room temperature. Quantitative velocity numbers are obtained by measuring the Doppler shift in the H two-photon excitation spectrum. Both the radial and axial velocity components are obtained by applying a perpendicular and an antiparallel excitation configuration, respectively. The required laser frequency calibration is accomplished by simultaneously recording the I 2 absorption spectrum with the fundamental frequency component of the laser system. This method, which is well-established in spectroscopic applications, enables us to achieve a relative accuracy in the transition frequency measurement below 10 Ϫ6 , corresponding to an accuracy in the velocity of approximately 200 m/s. This accuracy is nearly laser linewidth limited.

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Plasma Diagnostics

2022

Nonthermal Plasmas for Materials Processing

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Absolute calibration of atomic density measurements by laser-induced fluorescence spectroscopy with two-photon excitation

Cited by 282 publications

References 22 publications

Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

Plasma Diagnostics

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