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Bak J, Suazo Betancourt JL, Rekhy A, Abbasszadehrad A, Miles RB, Limbach CM, Walker MLR. High resolution spatially extended 1D laser scattering diagnostics using volume Bragg grating notch filters. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023; 94:023003. [PMID: 36859064 DOI: 10.1063/5.0121436] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Accepted: 01/18/2023] [Indexed: 06/18/2023]
Abstract
Laser light scattering systems with volume Bragg grating (VBG) filters, which act as spectral/angular filters, have often been used as a point measurement technique, with spatial resolution as low as a few hundred μm, defined by the beam waist. In this work, we demonstrate how VBG filters can be leveraged for spatially resolved measurements with several μm resolution over a few millimeters along the beam propagation axis. The rejection ring, as determined by the angular acceptance criteria of the filter, is derived analytically, and the use of the ring for 1D laser line rejection is explained. For the example cases presented,i.e., for a focused probe beam waist with a diameter of ∼150 μm, the rejection ring can provide resolution up to several millimeter length along the beam propagation axis for a 1D measurement, which is also tunable. Additionally, methods to further extend the measurable region are proposed and demonstrated, using a collimation lens with a different focal length or using multiple VBG filters. The latter case can minimize the scattering signal loss, without the tradeoff of the solid angle. Such use of multiple VBGs is to extend the measurable region along the beam axis, which differs from the commonly known application of multiple filters, to improve the suppression of elastic interferences. 1D rotational Raman and Thomson scattering measurements are carried out on pulsed and DC discharges to verify this method. The system features compactness, simple implementation, high throughput, and flexibility, to accommodate various experimental conditions.
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Affiliation(s)
- J Bak
- Department of Aerospace Engineering, Texas A&M University, 400 Bizzell St., College Station, Texas 77843, USA
| | - J L Suazo Betancourt
- Daniel Guggenheim School of Aerospace Engineering, Georgia Institute of Technology, North Ave. NW, Atlanta, Georgia 30332, USA
| | - A Rekhy
- Department of Aerospace Engineering, Texas A&M University, 400 Bizzell St., College Station, Texas 77843, USA
| | - A Abbasszadehrad
- Department of Aerospace Engineering, Texas A&M University, 400 Bizzell St., College Station, Texas 77843, USA
| | - R B Miles
- Department of Aerospace Engineering, Texas A&M University, 400 Bizzell St., College Station, Texas 77843, USA
| | - C M Limbach
- Department of Aerospace Engineering, Texas A&M University, 400 Bizzell St., College Station, Texas 77843, USA
| | - M L R Walker
- Daniel Guggenheim School of Aerospace Engineering, Georgia Institute of Technology, North Ave. NW, Atlanta, Georgia 30332, USA
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van de Steeg AW, Vialetto L, Silva AFSD, Viegas P, Diomede P, van de Sanden MCM, van Rooij GJ. The Chemical Origins of Plasma Contraction and Thermalization in CO 2 Microwave Discharges. J Phys Chem Lett 2022; 13:1203-1208. [PMID: 35089038 DOI: 10.1021/acs.jpclett.1c03731] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Thermalization of electron and gas temperature in CO2 microwave plasma is unveiled with the first Thomson scattering measurements. The results contradict the prevalent picture of an increasing electron temperature that causes discharge contraction. It is known that as pressure increases, the radial extension of the plasma reduces from ∼7 mm diameter at 100 mbar to ∼2 mm at 400 mbar. We find that, simultaneously, the initial nonequilibrium between ∼2 eV electron and ∼0.5 eV gas temperature reduces until thermalization occurs at 0.6 eV. 1D fluid modeling, with excellent agreement with measurements, demonstrates that associative ionization of radicals, a mechanism previously proposed for air plasma, causes the thermalization. In effect, heavy particle and heat transport and thermal chemistry govern electron dynamics, a conclusion that provides a basis for ab initio prediction of power concentration in plasma reactors.
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Affiliation(s)
| | - L Vialetto
- DIFFER, De Zaale 20, 5612AJ Eindhoven, The Netherlands
| | | | - P Viegas
- DIFFER, De Zaale 20, 5612AJ Eindhoven, The Netherlands
- Department of Physical Electronics, Faculty of Science, Masaryk University, Kotlářská 267/2, 611 37 Brno, Czech Republic
| | - P Diomede
- Faculty of Science and Engineering, Maastricht University, Paul Henri Spaaklaan 1, 6229 GS Maastricht, The Netherlands
| | | | - G J van Rooij
- DIFFER, De Zaale 20, 5612AJ Eindhoven, The Netherlands
- Faculty of Science and Engineering, Maastricht University, Paul Henri Spaaklaan 1, 6229 GS Maastricht, The Netherlands
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Klarenaar BLM, Guaitella O, Engeln R, Sobota A. How dielectric, metallic and liquid targets influence the evolution of electron properties in a pulsed He jet measured by Thomson and Raman scattering. ACTA ACUST UNITED AC 2018. [DOI: 10.1088/1361-6595/aad4d7] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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van den Bekerom DCM, Palomares Linares JM, van Veldhuizen EM, Nijdam S, van de Sanden MCM, van Rooij GJ. How the alternating degeneracy in rotational Raman spectra of CO 2 and C 2H 2 reveals the vibrational temperature. APPLIED OPTICS 2018; 57:5694-5702. [PMID: 30118084 DOI: 10.1364/ao.57.005694] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 06/01/2018] [Indexed: 06/08/2023]
Abstract
The contribution of higher vibrational levels to the rotational spectrum of linear polyatomic molecules with a center of symmetry (CO2 and C2H2) is assessed. An apparent nuclear degeneracy is analytically formulated by vibrational averaging and compared to numerical averaging over vibrational levels. It enables inferring the vibrational temperature of the bending and asymmetric stretching modes from the ratio of even to odd peaks in the rotational Raman spectrum. The contribution from higher vibrational levels is already observable at room temperature as g˜e/o=0.96/0.04 for CO2 and g˜e/o=1.16/2.84 for C2H2. The use of the apparent degeneracy to account for higher vibrational levels is demonstrated on spectra measured for a CO2 microwave plasma in the temperature range of 300-3500 K, and shown to be valid up to 1500 K.
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Vincent B, Tsikata S, Mazouffre S, Minea T, Fils J. A compact new incoherent Thomson scattering diagnostic for low-temperature plasma studies. ACTA ACUST UNITED AC 2018. [DOI: 10.1088/1361-6595/aabd13] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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