Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session NW1: Laser-Based Diagnostics IFocus
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Chair: Tsuyohito Ito, Osaka University Room: 1 |
Wednesday, October 12, 2016 3:00PM - 3:30PM |
NW1.00001: Development and application of laser-collision induced fluorescence for studying dynamic and structured plasmas Invited Speaker: Edward Barnat Laser collision-induced fluorescence (LCIF) is a powerful diagnostic which can be used for making temporally and spatially resolved measurements of electron densities in a plasma discharge. The technique, which involves the measurement of optical emission emanating from higher energy excited states due to the redistribution of the lower energy laser-excited state by collisions with energetic plasma species, has been readily employed to study both helium and argon discharges. In this presentation, an overview of the fundamental principles and anticipated limitations of the LCIF method will be presented. Examples of the LCIF method applied to structured and dynamic discharges generated in helium and argon will be presented to demonstrate the utility of this diagnostic technique. Finally, recent efforts used to extend the LCIF method to higher pressure (near atmospheric pressure) discharges will be discussed. [Preview Abstract] |
Wednesday, October 12, 2016 3:30PM - 3:45PM |
NW1.00002: Detection of beam-crossing Doppler shift using an optical vortex beam Mitsutoshi Aramaki, Shinji Yoshimura, Yasunori Toda, Tomohiro Morisaki, Kenichiro Terasaka, Masayoshi Tanaka Optical vortex (OV) beams are a set of solutions of the paraxial Helmholtz equation in the cylindrical coordinates, and its wave front has a spiral shape. The observer in the OV beam feels a three-dimensional Doppler effect, since the OV beam has the three-dimensional spiral wave front. We intend to improve the flexibility of the traditional Doppler spectroscopy using the OV beam. Since the multi-dimensional Doppler shifts are mixed into a single Doppler spectrum, we performed a modified saturated absorption spectroscopy to separate the Doppler components. The OV and plane wave are used as a probe beam and pump beam, respectively. The three-dimensional OV-beam's Doppler shifts define a tilted excitation volume in the velocity space. Therefore, the excitation volume of the plane-wave pump beam slices the tilted excitation volume of the OV beam. Since the configuration of the excitation volume depends on the location in the beam cross-section, the excitation volumes in the velocity space is mapped in the beam cross-section. The beam-crossing Doppler shift was observed as a local absorption dip in the probe-beam cross-section. The detail of optical vortex spectroscopy will be discussed in the presentation. [Preview Abstract] |
Wednesday, October 12, 2016 3:45PM - 4:00PM |
NW1.00003: High Sensitive Temperature Measurement of Microwave Plasma using Wavelength Modulation Spectroscopy Tohru Yamada, Makoto Matsui, Taito Kawakami Translational temperature is one of the key parameter to evaluate plasma conditions. In this study, we propose a novel method to determine the temperature using wavelength modulation spectroscopy. The peak value of second harmonic signal was measured as a function of the modulation depth. The translational temperature was estimated by fitting theoretically calculated curve to the characteristic curve. As a result of microwave argon discharge plasma, the estimated temperature shows good agreement with that measured by laser absorption spectroscopy using microwave argon plasma in the pressure range from 9.3 Pa to 446 Pa. [Preview Abstract] |
Wednesday, October 12, 2016 4:00PM - 4:15PM |
NW1.00004: Spatiotemporal Evolution of Ar($^{\mathrm{3}}$P$_{\mathrm{2}})$ Metastable Density Generated in a Pulsed DC Atmospheric Pressure micro-Plasma Jet Impinging on a Glass Plate K. Gazeli, G. Bauville, Et-T. Es-Sebbar, M. Fleury, O. Neveau, St. Pasquiers, J. Santos Sousa Atmospheric Pressure micro-Plasma Jets (APPJs) are promising tools in various domains such as biomedical and material treatments. In this work, APPJs are produced in pure argon at variable flow rates (i.e., 200, 400 and 600 sccm), by applying high voltage positive pulses (250 ns in FWHM and 6 kV in amplitude) at a repetition frequency of 20 kHz. The generated plasma impacts an ungrounded glass plate placed at a distance of 5 mm from the tube's orifice and perpendicular to the streamers propagation. At these conditions, a diffuse discharge is established resulting in a non-filamentary and reproducible plasma, in contrast with the free-jet case (no target). This allows the quantification of the absolute density of the Ar(1$s_{\mathrm{5}})$ metastable state by using laser absorption spectroscopy to probe the transition 1$s_{\mathrm{5}}\to $2$p_{\mathrm{9}}$ at 811.531 nm. The experiments show the dependence on the gas flow rate and on the axial and radial positions of the maximum density (6-9x10$^{\mathrm{13}}$ cm$^{\mathrm{-3}})$. At 200 sccm, it is obtained close to the tube's orifice, while with increasing flow rate it is displaced towards the plate. Regarding the radial variation, density maxima are obtained in a small area around the streamers propagation axis. [Preview Abstract] |
Wednesday, October 12, 2016 4:15PM - 4:30PM |
NW1.00005: Cavity-enhanced absorption spectroscopy to characterize atmospheric pressure plasma jets Jean-Pierre van Helden, Andy Nave, Stephan Reuter, Juergen Roepcke, Michele Gianella, Grant Ritchie Non-equilibrium atmospheric pressure plasma jets gain more and more interest as their technological applications increase in diverse fields such as material processing and plasma medicine. Hence, it is essential to diagnose the fluxes of the species generated by these plasma sources to identify relevant fundamental processes and to improve process efficiency. Especially for a comprehensive understanding of the kinetics of the transient species involved, high precision measurements of reactive molecular precursors, free radicals and to identify of any short lived species are of crucial importance. However, the detection of transient species in these type of plasmas poses a challenge for diagnostic techniques as the plasmas typically have small dimensions and high density gradients in space and time. We have overcome these limitations by using cavity-enhanced absorption spectroscopy (CEAS). In this contribution, the latest results concerning the detection of transient species in two types of plasma jets employing CEAS in the near- and mid-infrared spectral range will be presented. We will show that with these methods spatially resolved investigations of concentrations in the mm sized effluent of the plasma jet can be achieved. [Preview Abstract] |
Wednesday, October 12, 2016 4:30PM - 4:45PM |
NW1.00006: An improved model to analyze Langmuir probe assisted photo-detachment signal for measuring electronegative plasma parameters Nishant Sirse, Noureddine Oudini, Abderrezeg Bendib, Albert R Ellingboe A diagnostic technique for measuring negative ion parameters based on Langmuir probe assisted laser photo-detachment relies on a theoretical model which relates the rise in the electron saturation current to electronegativity in the plasma. The existing model depend on various assumptions and neglect electrostatic potential barrier formed between the laser column (electropositive column) and the surrounding electronegative plasma in order to prevent the outward flow of electrons from the electropositive plasma column. These assumptions leads to erroneous estimation of the plasma electronegativity. In the present work, we present an analytical model to analyze Langmuir probe assisted photo-detachment signal in order to improve the accuracy of measured electronegativity and extended this technique for measuring electron temperature and charged species density. The analytical model is validated using both experiments and particle-in-cell simulation. The results shows improved accuracy in the measured parameters when compared to existing model. [Preview Abstract] |
Wednesday, October 12, 2016 4:45PM - 5:00PM |
NW1.00007: Real-time monitoring of reactive species in downstream etch reactor by VUV broad-band absorption spectroscopy. R. Soriano, L. Vallier, G. Cunge, N. Sadeghi Plasma etching of nanometric size, high aspect-ratio structures is more challenging at each new technological node. Remote plasmas are beginning to find use when damages on nanostructures by ion bombardment become critical or when etching with high selectivity on different materials present on the wafer is necessary ($i.e.$ tungsten oxide etching with fluorine and hydrogen containing plasmas in remote reactor from AMAT). Furthermore, it is expected that downstream plasma will replace many wet chemical etching processes to alleviate the issue of ~pattern collapses caused by capillary forces when nanometer size high aspect ratio structures are immersed in liquids. ~In these downstream plasmas, radicals are the main active species and a control of their density is of prime importance. Most of gases used and radicals produced in etching plasmas (HBr, BrCl, Br$_{\mathrm{2}}$, NF$_{\mathrm{3}}$, CH$_{\mathrm{2}}$F$_{\mathrm{2}}$,\textellipsis ) have strong absorption bands in the vacuum UV spectral region and we have shown that very low concentration of these species can be detected by VUV absorption [1]. We have recently improved the technique by using a VUV CCD camera, instead of the PMT, which render possible the Broad-Band absorption spectroscopy in the 120-200 nm range, with a deuterium lamp, or a laser produced xenon arc lamp as light source. The multi-spectral detection ability of the CCD reduces the acquisition time to less than 1 second and can permit the real time control of the process control. [1] G. Cunge \textit{et al}, J. Phys. D~: Appl. Phys. \textbf{44} (2011) 122001. [Preview Abstract] |
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