Thomson, Raman and Rayleigh scattering on atmospheric
plasma
Citation for published version (APA):
Gessel, van, A. F. H., Carbone, E. A. D., Pageau, A., Bruggeman, P. J., & Mullen, van der, J. J. A. M. (2010). Thomson, Raman and Rayleigh scattering on atmospheric plasma. In Proceedings of the XX European Conference on the Atomic and Molecular Physics of Ionized Gases (20th ESCAMPIG, Novi Sad, Serbia, July 13-17, 2010) (pp. P2.34-1/2)
Document status and date: Published: 01/01/2010 Document Version:
Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:
• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.
• The final author version and the galley proof are versions of the publication after peer review.
• The final published version features the final layout of the paper including the volume, issue and page numbers.
Link to publication
General rights
Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain
• You may freely distribute the URL identifying the publication in the public portal.
If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement:
www.tue.nl/taverne
Take down policy
If you believe that this document breaches copyright please contact us at:
openaccess@tue.nl
providing details and we will investigate your claim.
Thomson, Raman and Rayleigh scattering on atmospheric plasmas
A.F.H. van Gessel*, E. Carbone, A. Pageau, P.J. Bruggeman,J.J.A.M. van der Mullen
Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
*
a.f.h.v.gessel@tue.nl
Introduction
Atmospheric pressure plasmas are the subject of growing interest, due to their applicabil-ity in many fields, including material processing, surface treatment and medical applica-tions like wound healing and bacterial inactivation [1]. The discharges have relatively low gas temperatures and are non-LTE, and have the practical advantage that there is no need for a complicated vacuum system.
Plasma sources
In this paper we describe active spectroscopy measurements performed on two types of atmospheric pressure plasma’s: a surfatron microwave discharge and a pulsed RF jet. In the case of the surfatron microwaves of 2.45 GHz are coupled into the plasma via a sur-fatron launcher device [2]. The plasma is sustained inside a capillary tube.
In the RF jet a ring electrode is mounted around a capillary tube, and a grounded electrode is positioned after the end of the tube. The electrode is connected to a high voltage RF power source (15.6 MHz), which is pulsed such that the discharge is switched on about 5% of the time.
As a gas mixture we use mainly helium or argon, with a small amount of oxygen.
Laser scattering
Three types of laser scattering are monitored: Rayleigh scattering (scattering on heavy particles), Thomson scattering (scattering on free electrons) and Raman scattering (scat-tering on molecules). We use a laser beam from a pulsed Nd:YAG laser (532 nm), which is focused inside the plasma near the end of the capillary tube.
Rayleigh Scattering is used to determine the gas temperature Tg. The intensity of
the signal is proportional to the heavy particle density, which–with known pressure– gives Tg.
Thomson Scattering is used to determine the electron temperature Te and the
elec-tron density ne. ne is proportional to the intensity of the signal, while Te is provided by the
Doppler broadening. The Thomson signal is very weak, and can easily be obscured by the Rayleigh signal and false stray light. The Thomson signal however is much more Doppler broadened than the Rayleigh signal, which makes it possible to filter out the Rayleigh signal by applying a notch filter. This filtering is done optically by the use of a Triple Grating Spectrometer (TGS) [3].
The third type of laser scattering is Raman Scattering, mainly from O2 and N2. It is
used for the calibration of the wavelength of the TGS and the absolute intensity. The intensity needs to be absolutely calibrated in order to calculate the electron density from
Topic number: 5 Plasma diagnostics
the Thomson signal. The Raman signal can also be used for determining the temperatures and densities of O2 and N2. Since the experiments are done in ambient air, Raman
scat-tering is always present. Separating the Thomson signal from the Raman signal is done by a specially designed fitting process. An example of a Raman signal is shown in fig-ure 1. An example of a Thomson signal with a superimposed Raman signal is shown in figure 2.
Figure 1. Raman signal of ambient air at room temperature (300 K). The fit is used to calibrate the wavelength and absolute intensity of the setup.
Figure 2. Thomson signal with superimposed Raman signal of a surfatron plasma with argon. The Thomson signal has a Gaussian shape, where the width gives the electron temperature and the intensity the electron density.
References
[1] L.J.M. van den Bedem, R.E.J. Sladek, M. Steinbuch and E. Stoffels, conf. proc. 27th ICPIG 18 (2005)
[2] M. Moisan, Z. Zakrzewski and R. Pantel, J. Phys. D: Appl. Phys. 12, 219 (1979) [3] N. de Vries, J.M. Palomares, W.J. van Harskamp, E. Iordanova, G.M.W. Kroesen and J.J.A. van der Mullen, J. Phys. D: Appl. Phys. 41, 105209 (2008)
