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Quantitative raman thermometry and N2+ detection in a non-transferred plasma torch

Nilsson, Sebastian LU ; Ivanoff, Aurélien ; Zubairova, Alsu LU ; Siddanathi, Likitha ; Sepman, Alexey ; Wiinikka, Henrik ; Westerberg, Lars Göran ; Aldén, Marcus LU ; Brackmann, Christian LU and Ehn, Andreas LU (2026) In Optics and Lasers in Engineering 200.
Abstract

Quantitative laser-based diagnostics like Raman spectroscopy are essential for studying high-temperature processes, but their application in intensely luminous and transient environments such as plasma torches is severely limited by overwhelming background emission. This study focuses on the quantitative thermometry of a 7 kW atmospheric air plasma jet, an environment where such measurements are notoriously difficult. To enable these measurements, a Polarization Lock-In Filtering (PLF) Raman technique is used to suppress the intense and fluctuating plasma background. The method successfully yields high-quality N2 ro-vibrational spectra along the jet's central axis. Model-based fitting of these spectra produces a detailed... (More)

Quantitative laser-based diagnostics like Raman spectroscopy are essential for studying high-temperature processes, but their application in intensely luminous and transient environments such as plasma torches is severely limited by overwhelming background emission. This study focuses on the quantitative thermometry of a 7 kW atmospheric air plasma jet, an environment where such measurements are notoriously difficult. To enable these measurements, a Polarization Lock-In Filtering (PLF) Raman technique is used to suppress the intense and fluctuating plasma background. The method successfully yields high-quality N2 ro-vibrational spectra along the jet's central axis. Model-based fitting of these spectra produces a detailed axial temperature profile, showing a decay from over 3700 K near the nozzle. Furthermore, the high signal quality enabled the detection of singly ionized nitrogen (N2+) in the plasma core, providing direct evidence of its ionized state. These results represent the first application of PLF for thermometry in a plasma torch and provide critical experimental data for validating magnetohydrodynamic simulations.

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author
; ; ; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Plasma diagnostics, Plasma torch, Polarization lock-In filtering (PLF), Raman spectroscopy, Thermal plasma, Thermometry
in
Optics and Lasers in Engineering
volume
200
article number
109583
publisher
Elsevier
external identifiers
  • scopus:105027099558
ISSN
0143-8166
DOI
10.1016/j.optlaseng.2025.109583
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2025 The Author(s)
id
7141b3fd-15e9-44be-bba0-274cc8c0c87a
date added to LUP
2026-03-13 13:43:43
date last changed
2026-03-17 15:36:40
@article{7141b3fd-15e9-44be-bba0-274cc8c0c87a,
  abstract     = {{<p>Quantitative laser-based diagnostics like Raman spectroscopy are essential for studying high-temperature processes, but their application in intensely luminous and transient environments such as plasma torches is severely limited by overwhelming background emission. This study focuses on the quantitative thermometry of a 7 kW atmospheric air plasma jet, an environment where such measurements are notoriously difficult. To enable these measurements, a Polarization Lock-In Filtering (PLF) Raman technique is used to suppress the intense and fluctuating plasma background. The method successfully yields high-quality N<sub>2</sub> ro-vibrational spectra along the jet's central axis. Model-based fitting of these spectra produces a detailed axial temperature profile, showing a decay from over 3700 K near the nozzle. Furthermore, the high signal quality enabled the detection of singly ionized nitrogen (N<sub>2</sub><sup>+</sup>) in the plasma core, providing direct evidence of its ionized state. These results represent the first application of PLF for thermometry in a plasma torch and provide critical experimental data for validating magnetohydrodynamic simulations.</p>}},
  author       = {{Nilsson, Sebastian and Ivanoff, Aurélien and Zubairova, Alsu and Siddanathi, Likitha and Sepman, Alexey and Wiinikka, Henrik and Westerberg, Lars Göran and Aldén, Marcus and Brackmann, Christian and Ehn, Andreas}},
  issn         = {{0143-8166}},
  keywords     = {{Plasma diagnostics; Plasma torch; Polarization lock-In filtering (PLF); Raman spectroscopy; Thermal plasma; Thermometry}},
  language     = {{eng}},
  month        = {{01}},
  publisher    = {{Elsevier}},
  series       = {{Optics and Lasers in Engineering}},
  title        = {{Quantitative raman thermometry and N<sub>2</sub><sup>+</sup> detection in a non-transferred plasma torch}},
  url          = {{http://dx.doi.org/10.1016/j.optlaseng.2025.109583}},
  doi          = {{10.1016/j.optlaseng.2025.109583}},
  volume       = {{200}},
  year         = {{2026}},
}