| 1. |
- Kiefer, Johannes, et al.
(author)
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Laser-induced breakdown flame thermometry
- 2012
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In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 159:12, s. 3576-3582
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Journal article (peer-reviewed)abstract
- The determination of temperature distribution is an essential task when flames are characterized. We propose a new approach for flame thermometry based on laser-induced breakdown spectroscopy (LIBS) utilizing the temperature dependency of the breakdown threshold laser pulse energy. Calibration measurements are carried out in heated gas flows and post-combustion gases. Compositional effects on the breakdown threshold are corrected employing a straightforward procedure. For this purpose, the elemental composition is derived from the LIBS spectra and this information is then used for correcting the measured threshold laser pulse energy. A series of proof-of-concept measurements in a laminar methane/air flame on a Bunsen burner is conducted and compared to reference data from coherent anti-Stokes Raman scattering (CARS). The corrected LIBS temperatures show excellent agreement with those obtained by CARS. Therefore, our approach represents a simple and straightforward alternative to traditionally used thermometry methods. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 2. |
- Kiefer, Johannes, et al.
(author)
-
Laser-induced breakdown spectroscopy : A simple but versatile tool for combustion diagnostics
- 2012
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In: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2012. - Washington, D.C. : OSA. - 9781557529336
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Conference paper (peer-reviewed)abstract
- Laser-induced breakdown spectroscopy (LIBS) is an experimentally simple method capable of measuring elemental composition in a flame. Moreover, the breakdown threshold energy is temperature dependent. Hence, LIBS allows multiple parameter determination in combustion environments.
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| 3. |
- Kiefer, Johannes, et al.
(author)
-
Local composition and temperature determination in laminar flames by laser-induced plasma diagnostics
- 2011
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In: 2011 Conference on Lasers and Electro-Optics : Laser Science to Photonic Applications, CLEO 2011 - Laser Science to Photonic Applications, CLEO 2011. - 9781557529107
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Conference paper (peer-reviewed)abstract
- We utilize laser-induced breakdown spectroscopy for measuring mixture composition and temperature in flames. Spectroscopy of the plasma emission yields concentration information, while temperature is derived from the breakdown threshold pulse energy.
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| 4. |
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| 5. |
- Bloß, Dana, et al.
(author)
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X-ray radiation damage cycle of solvated inorganic ions
- 2024
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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 15:1
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Journal article (peer-reviewed)abstract
- X-ray-induced damage is one of the key topics in radiation chemistry. Substantial damage is attributed to low-energy electrons and radicals emerging from direct inner-shell photoionization or produced by subsequent processes. We apply multi-electron coincidence spectroscopy to X-ray-irradiated aqueous solutions of inorganic ions to investigate the production of low-energy electrons (LEEs) in a predicted cascade of intermolecular charge- and energy-transfer processes, namely electron-transfer-mediated decay (ETMD) and interatomic/intermolecular Coulombic decay (ICD). An advanced coincidence technique allows us to identify several LEE-producing steps during the decay of 1s vacancies in solvated Mg2+ ions, which escaped observation in previous non-coincident experiments. We provide strong evidence for the predicted recovering of the ion’s initial state. In natural environments the recovering of the ion’s initial state is expected to cause inorganic ions to be radiation-damage hot spots, repeatedly producing destructive particles under continuous irradiation.
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| 6. |
- Ehn, Andreas, et al.
(author)
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Advanced laser-based techniques for gas-phase diagnostics in combustion and aerospace engineering
- 2017
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In: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 71:3, s. 341-366
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Research review (peer-reviewed)abstract
- Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics.
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| 7. |
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| 8. |
- Kazemi, Mehdi Mohammad, et al.
(author)
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Influence of the alkyl side-chain length on the ultrafast vibrational dynamics of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide (C(n)mimNTf(2)) ionic liquids
- 2017
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:24, s. 15988-15995
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Journal article (peer-reviewed)abstract
- Probing the vibrational dynamics of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (CnmimNTf2) ionic liquids (ILs) using femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) has indicated the ultrafast vibrational energy transfer between counter ions which is governed by interionic interactions and facilitated by hydrogen bonds. In this study, fs-CARS is used to investigate the ultrafast dynamics of the vibrational modes of the CnmimNTf2 ILs with n = 6, 8, 10, and 12 in a spectral region, which involves the imidazolium ring and the alkyl side-chain vibrations. The vibrational Raman modes with wavenumbers around 1418 cm−1 are excited through the CARS process and the ultrafast time evolution of the consequently excited vibrational modes is monitored. The investigation of the life times of the fs-CARS transient signals indicates that the time scale of the dynamics becomes much faster when the alkyl side-chain length of the CnmimNTf2 is longer than n = 8. This observation suggests an increase in the hydrogen bonding interactions due to the nano-structuring of the ionic liquids, which became evident with an increasing length of the alkyl side-chain. This behavior is also found in molecular dynamics simulations. There, an increase of the oxygen density around the C(2)–H moiety of the imidazolium ring, which is the predominant site for hydrogen bond formation, is observed. In other words, the longer the alkyl side-chain, the more reorganization of the ionic liquid into polar and non-polar domains occurs and the higher the probability of finding interionic hydrogen bonds at the C(2)–H position becomes.
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| 9. |
- Kiefer, Johannes, et al.
(author)
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Gas-Phase and Combustion Diagnostics by Infrared Laser-Induced Grating Spectroscopy
- 2016
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In: Optics and Photonics for Energy and the Environment, E2 2016. - 9781557528209
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Conference paper (peer-reviewed)abstract
- Infrared laser-induced grating spectroscopy (IR-LIGS) is a powerful method for the detection of molecules in atmospheric and combustion chemistry by exploiting their strong and species-specific fundamental vibrations. This work discusses potentials and limitations of the method.
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| 10. |
- Kiefer, Johannes, et al.
(author)
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Impact of plasma dynamics on equivalence ratio measurements by laser-induced breakdown spectroscopy
- 2015
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In: Applied Optics. - 2155-3165. ; 54:13, s. 4221-4226
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Journal article (peer-reviewed)abstract
- The systematic errors introduced by triggering a USB spectrometer for laser-induced breakdown spectroscopy equivalence ratio measurements are studied. We analyze the temporal behavior of laser-induced plasma in a nonreacting methane/air mixture and investigate the influence of the dynamics on equivalence ratio measurements with gated and ungated detection. For use of gated detectors, optimal delay times were found to be between 500 and 2000 ns to allow effective suppression of interferences while maintaining sufficient signal-to-noise levels. Good precision was found for short and long exposure time intervals when an intensified CCD camera was employed. On the other hand, the jitter of an externally triggered ungated spectrometer leads to high uncertainties. Running the ungated spectrometer freely, the single-shot uncertainty can be reduced by more than 1 order of magnitude. (C) 2015 Optical Society of America
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