Bulletin of the American Physical Society
62nd Annual Gaseous Electronics Conference
Volume 54, Number 12
Tuesday–Friday, October 20–23, 2009; Saratoga Springs, New York
Session FT3: Laser Based Diagnostics at High Pressure |
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Chair: Timo Gans, Queen's University Belfast Room: Saratoga Hilton Ballroom 3 |
Tuesday, October 20, 2009 8:00AM - 8:15AM |
FT3.00001: Dynamics of dielectric barrier discharge in non-uniform gas composition investigated by laser spectroscopic measurements Keiichiro Urabe, Yosuke Ito, Joon-Young Choi, Osamu Sakai, Kunihide Tachibana It is well known that stable and glow dielectric barrier discharge (DBD) at atmospheric pressure is observed using helium gas and AC high voltage of kHz-order frequency. We have investigated the discharge mechanisms of DBDs from a view point of the spatiotemporal distributions of excited species measured by laser spectroscopic methods. In this presentation, we will show convincing arguments about the discharge model of the DBD especially having the non-uniformity of gas composition. As a DBD plasma source for atmospheric pressure processes, we have investigated an atmospheric pressure plasma jet (APPJ) using helium gas flow in ambient air, and this plasma source can be regarded as the DBD near the boundary interface of helium gas and ambient air. In this APPJ, we observed spatiotemporal distributions of excited species density inside the helium gas channel, using laser absorption spectroscopy and laser induced fluorescence, to measure the densities of helium metastable atom (2$^{3}$S$_{1}$ state) and nitrogen ion (X$^{2}\Sigma _{g}^{+}$ state) respectively. To study the influence of nitrogen gas contamination on the discharge profile of DBD, we have also applied CO$_{2}$-laser heterodyne interferometry to measure the special distribution of electron density in parallel-plate DBD. [Preview Abstract] |
Tuesday, October 20, 2009 8:15AM - 8:30AM |
FT3.00002: Electric field measurements in near-atmospheric pressure nitrogen and air based on a four-wave mixing scheme Sarah Mueller, Tsuyohito Ito, Kazunobu Kobayashi, Dirk Luggenhoelscher, Uwe Czarnetzki, Satoshi Hamaguchi Electric field induced coherent Raman scattering (E-CRS) measurement is a promising technique for measuring electric fields in high-pressure environments and was first demonstrated with hydrogen molecules. In this study, we have demonstrated electric field measurements by using nitrogen molecules. Two pulsed ns laser beams (532 nm and 607 nm) are employed for the measurement. In nitrogen molecules those two laser beams together with the electric field induce a coherent IR signal at a wavelength of 4.29 $\mu $m. In our current experimental setup, the minimum detectable field strength in open air is about 100 Vmm-1, which is sufficiently small compared with the average field present in typical microdischarges. No further knowledge of other gas/plasma parameters such as the nitrogen density is required for the measurement. Further details on the techniques as well as measurement results in microdischarges will be presented. [Preview Abstract] |
Tuesday, October 20, 2009 8:30AM - 8:45AM |
FT3.00003: Argon microplasma diagnostics by diode laser absorption Naoto Miura, Jun Xue, Jeffrey Hopwood Argon kinetic gas temperature and line integrated resonance state (1s$_{4})$ density in argon microplasma at 1-760 Torr were estimated by diode laser absorption. A 900 MHz microstrip split ring resonator (MSRR) was used as the microplasma generator. An argon atomic transition at 810.4 nm (1s$_{4}$-2p$_{7})$ was chosen as the absorption line. The wavelength of a single-mode laser diode was tuned by changing the diode case temperature. The absorption line was scanned by modulating the laser driving current. The laser output was collimated and passed through a 0.5 mm hole drilled between the MSRR electrodes where the microplasma was sustained. The absorption profile was fit with a Voigt function. The gas temperature was estimated from the broadening, and the line integrated density of the argon resonance state (1s$_{4})$ was obtained from the integral of the absorption profile. The line integrated densities of argon 1s$_{4}$ were 1.7x10$^{15}$ m$^{-3}$ m at 1 Torr and 1.4x10$^{15}$ m$^{-3}$ m at 760 Torr with 1W of input power. The visually observed length of plasma decreased from 1 cm at 1 Torr to a few hundred microns at 760 Torr. The measured gas temperature increased from 350 K at 1 Torr to 750 K at 760 Torr. The microplasma was also simulated using a fluid model, which will be compared with experimental measurements. [Preview Abstract] |
Tuesday, October 20, 2009 8:45AM - 9:00AM |
FT3.00004: Dissociation profiles of oxygen in a capacitively coupled atmospheric pressure discharge Nikolas Knake, Daniel Schr\"oder, Volker Schulz-von der Gathen, J\"org Winter The creation of atomic oxygen in a capacitively coupled jet type discharge is investigated using spatially resolved xenon calibrated TALIF and OES. The discharge is a planar jet type 13.56MHz rf device of 1x1 mm$^{2}$ discharge cross section and an electrode length of 40 mm using a 1.4 slm helium base gas flow containing a small amount of molecular oxygen being dissociated in the discharge. The spatial build up of the dissociation profiles along the first few millimeters of the discharge channel is investigated as well as the inter electrode distribution. Studies on the variation of transmitter power, gas flux and gas mixture were performed in the plasma itself, the effluent and the transition area from plasma to effluent. To get an insight into the production and destruction processes of the oxygen molecules, it is a prerequisite to understand the atomic density build up in the plasma and the decay especially inside the transition region between core plasma and effluent. Even several millimeters outside the discharge in the effluent atomic oxygen can be found with densities up to some 10$^{14}$ cm$^{-3}$. This project is supported by the DFG in the framework of ``FOR1123'', ``SCHU-2353/1'', and the ``Research School der Ruhr-Universit\"{a}t Bochum''. [Preview Abstract] |
Tuesday, October 20, 2009 9:00AM - 9:15AM |
FT3.00005: Determination of Absolute Number Densities of OH Radicals in an Atmospheric Microwave Plasma Jet Using Cavity Ringdown Spectroscopy Chuji Wang, Nimisha Srivastava, Theodore S. Dibble Identification and quantification of reactive plasma species in the downstream part of an atmospheric plasma jet remain less explored; and how far a reactive species can exist in the downstream and its formation mechanism remain little known. The objective of this work was to employ the UV-cavity ringdown spectroscopy technique to explore how far OH radicals can exist in the downstream zone of a small-scale (3 - 12 mm) atmospheric argon microwave plasma jet. We report on observation of the OH radicals existing in far downstream of the plasma jet column. The ``far'' downstream is characterized by the ratio of the distance from the jet orifice to the length of the jet column. In this work, the far downstream is referred to as the location, where the ratio is $>$ 3. Absolute number densities of the OH radicals in the far downstream part as well as in the jet column were measured. Discussion of the source of the OH radicals is also given. [Preview Abstract] |
Tuesday, October 20, 2009 9:15AM - 9:30AM |
FT3.00006: Collective Thomson Scattering Diagnostics of Laser Produced Plasmas for EUV Light Sources Kentaro Tomita, Yasuhisa Hyakuta, Kota Ohara, Kiichiro Uchino Extreme ultraviolet (EUV) lights are going to be used for semiconductor lithography after the 32 nm half-pitch technology node. For EUV light sources, high density (electron density $n_{e}$=10$^{24}$ - 10$^{26}$ m$^{-3})$ and high temperature (electron temperature $T_{e}$= 10 - 30 eV) plasmas should be generated using Xe or Sn atoms. In order to produce required EUV lights efficiently, plasma parameters such as $n_{e}$, $T_{e}$ and averaged ionic charge $\bar {Z}$ should be optimized. We have tried to apply the LTS measurement to EUV plasmas. When we use a visible laser as a probing laser, the LTS spectra from the EUV plasmas are in the collective regime. The spectrum of the collective Thomson scattering consists of an ion term and an electron term. Taking account of the strong background radiation from the plasma, we determined to measure the ion term, for which we could expect enough SN ratios against the background radiation. One problem to measure the ion term is that the spectral resolution of 10 pm is needed, and the other problem is that the intense wall-scattered laser lights easily overwhelm the ion spectra. In order to overcome these problems, we constructed a newly designed LTS measurement system whose spectral resolution and stray light rejection were enough to resolve fine feature of the ion term. [Preview Abstract] |
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