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| 2. |
- Kristensson, Elias, et al.
(författare)
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Modeling of the SLIPI technique with the large scatterer approximation of the RTE
- 2017
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Ingår i: 2017 32nd General Assembly and Scientific Symposium of the International Union of Radio Science.
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Konferensbidrag (refereegranskat)abstract
- To overcome the blur when visualizing of the interior of a turbid media by means light-based methods, a technique called Structured Laser Illumination Planar Imaging (SLIPI) is employed. The method is based on a 'light coding' strategy to distinguish between directly and multiply scattered light, allowing the intensity from the latter to be suppressed by post-processing data. In this paper, we explain the origin of the deviations between SLIPI measurements and the results obtained by the Bouguer-Beer law. The explanation employs the large scatterer approximation of the Radiative Transfer Equation. Our results indicate that forward-scattering can lead to deviations between experiments and theoretical predictions, especially when probing relatively large particles.
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| 3. |
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| 4. |
- Kristensson, Elias, et al.
(författare)
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Physical explanation of the SLIPI technique by the large scatterer approximation of the RTE
- 2017
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073. ; 189, s. 112-125
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Tidskriftsartikel (refereegranskat)abstract
- Visualizing the interior of a turbid scattering media by means light-based methods is not a straightforward task because of multiple light scattering, which generates image blur. To overcome this issue, a technique called Structured Laser Illumination Planar Imaging (SLIPI) was developed within the field of spray imaging. The method is based on a ‘light coding’ strategy to distinguish between directly and multiply scattered light, allowing the intensity from the latter to be suppressed by means of data post-processing. Recently, the performance of the SLIPI technique was investigated, during which deviations from theoretical predictions were discovered. In this paper, we aim to explain the origin of these deviations, and to achieve this end, we have performed several SLIPI measurements under well-controlled conditions. Our experimental results are compared with a theoretical model that is based on the large scatter approximation of the Radiative Transfer Equation but modified according to certain constraints. Specifically, our model is designed to (1) ignore all off-axis intensity contributions, (2) to treat unperturbed- and forward-scattered light equally and (3) to accept light to scatter within a narrow forward-cone as we believe these to the rules governing the SLIPI technique. The comparison conclusively shows that optical measurements based on scattering and/or attenuation in turbid media can be subject to significant errors if not all aspects of light-matter interactions are considered. Our results indicate, as were expected, that forward-scattering can lead to deviations between experiments and theoretical predictions, especially when probing relatively large particles. Yet the model also suggests that the spatial frequency of the superimposed ‘light code’ as well as the spreading of the light-probe are important factors one also needs to consider. The observed deviations from theoretical predictions could, however, potentially be exploited to assess particle size
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| 5. |
- Andersson, David, et al.
(författare)
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A light-efficient and versatile multiplexing method for snapshot spectral imaging
- 2024
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Ingår i: Scientific Reports. - 2045-2322. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- The study of rapid and stochastic events that involve multiple species, such as chemical reactions and plasma dynamics, requires means to capture multispectral information in two dimensions at both high temporal- and spatial resolution. Commercially available cameras that provide high temporal resolution are based on either signal intensification or rapid data acquisition. Intensified cameras provide extremely short acquisition times using intensification by means of micro channel plates, but the conversion between electrons and photons makes these cameras inherently monochrome. In contrast, high-speed cameras can achieve color-sensitivity through integrated Bayer filters but suffer from a reduced light collection efficiency and a fixed spectral composition. In this article we present a non-integrated optical arrangement for instantaneous multispectral imaging based on FRAME image multiplexing. By spectrally separating the signal using lossless dichroic mirrors, a 16-fold increase in light-collection efficiency is gained (compared to past solutions), resulting in an equivalent increase in temporal resolution. This improvement provides new avenues for multispectral imaging of rapid events. We demonstrate the system’s versatility and suitability for studies of such processes by applying it for (i) temperature mapping using a high-resolution CCD camera, (ii) high-speed videography up to 10 kHz at four spectral channels and (iii) dual-species visualization in a plasma discharge using an intensified sCMOS camera.
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| 6. |
- Andersson, David, et al.
(författare)
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Multispectral snapshot highspeed imaging using periodic shadowing multiplexing
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics, CLEO 2023. - 9781957171258
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Konferensbidrag (refereegranskat)abstract
- We present a lightefficient multiplexed imaging setup that can be used with any monochrome camera and combine it with a highspeed camera to achieve highspeed multispectral imaging with no loss in capture rate or FOV.
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| 7. |
- Bao, Yupan, et al.
(författare)
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Effect of a single nanosecond pulsed discharge on a flat methane–air flame
- 2023
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Ingår i: Applications in Energy and Combustion Science. - 2666-352X. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- Successful implementation of plasma-assisted combustion in applied thermal processes heavily relies on how the plasma can be formed as it interacts with the reactive flow and what the effects are of such a plasma on the combustion process. The current study is an experimental investigation of a plasma-assisted lifted flat methane–air flame by a nanosecond pulsed discharge at atmospheric pressure. The nanosecond pulsed discharge, with a pulse duration of 4 ns and an amplitude of 30 kV to 50 kV, is used to stimulate the flame with a repetition rate of 1 Hz. The flame/plasma interactions are investigated with electrical and optical/laser diagnostics to study plasma-formation and its effect on the temperatures and formaldehyde formation. The flame speed seems to be accelerated for tens of milliseconds after the plasma stimulation, without noticeable gas temperature increase at the flame front and in the post-flame region. Formaldehyde is formed in the unburnt region while there is a slight increase in formaldehyde signal in the preheat zone. These results show that a volumetric effect of plasma-assisted combustion can be achieved with a short nanosecond plasma from a single excitation.
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| 8. |
- Bao, Yupan, et al.
(författare)
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Improved temporal contrast of streak camera measurements with periodic shadowing
- 2021
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Ingår i: Optics Letters. - 0146-9592. ; 46:22, s. 5723-5726
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Tidskriftsartikel (refereegranskat)abstract
- Periodic shadowing, a concept used in spectroscopy for stray light reduction, has been implemented to improve the temporal contrast of streak camera imaging. The capabilities of this technique are first proven by imaging elastically scattered picosecond laser pulses and are further applied to fluorescence lifetime imaging, where more accurate descriptions of fluorescence decay curves were observed. This all-optical approach can be adapted to various streak camera imaging systems, resulting in a robust technique to minimize space-charge induced temporal dispersion in streak cameras while maintaining temporal coverage and spatial information.
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| 9. |
- Bao, Yupan, et al.
(författare)
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Single-shot 3D imaging of hydroxyl radicals in the vicinity of a gliding arc discharge
- 2021
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Ingår i: Plasma Sources Science and Technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 30:4
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Tidskriftsartikel (refereegranskat)abstract
- Chemical processing by plasma is utilized in many applications. Plasma-related studies, however, are challenging to carry out due to plasmas' transient and unpredictable behavior, excessive luminosity emission, 3D complexity and aggressive chemistry and physiochemical interactions that are easily affected by external probing. Laser-induced fluorescence is a robust technique for non-intrusive investigations of plasma-produced species. The hydroxyl radical (OH) is an interesting molecule to target, as it is easily produced by plasmas in humid air. In this letter, we present 3D distributions of ground state OH radicals in the vicinity of a glow-type gliding arc plasma. Such radical distributions, with minimal plasma emission, are captured instantaneously in one single camera acquisition by combining structured laser illumination and a lock-in based imaging analysis method called FRAME. The orientation of the plasma discharge can be reconstructed from the 3D data matrix, which can then be used to calculate 2D distributions of ground state OH radicals in a plane perpendicular to the orientation of the plasma channel. Our results indicate that OH distributions around a gliding arc are strongly affected by gas dynamics. We believe that the ability to instantaneously capture 3D transient molecular distributions in a plasma discharge, with minimal plasma emission interference, will have a strong impact on the plasma community for in-situ investigations of plasma-induced chemistry and physics.
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| 10. |
- Berrocal, Edouard, et al.
(författare)
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Analysis of the SLIPI technique for multiple scattering suppression in planar imaging of fuel sprays
- 2009
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Ingår i: 11th Triennial International Annual Conference on Liquid Atomization and Spray Systems. - 9781617826535
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Konferensbidrag (refereegranskat)abstract
- Structured Laser Illumination Planar Imaging (SLIPI) is a new laser sheet based diagnostic able to significantly increase the contrast of spray images by removing the multiple scattering noise contribution. The technique has been recently developed and applied to the study of a conventional hollow-cone water spray, where the transmission through the near-field spray was 26%. In such condition, it has been shown that 44% of the total optical signal, corresponding to multiply scattered photons, could be removed. In order to now employ the technique to more challenging sprays, such as air-blast atomizer and Diesel sprays, where the transmission can be reduced down to ~0.25%, further investigations and refinements of the approach are required. This article focuses on the analysis, optimization and application of SLIPI for fuel sprays by means of a modern 3-dimensional computational model. The simulation is performed via a validated Monte Carlo code in association with a ray-tracing approach, to simulate the propagation of the incident laser radiation through the spray and the collection optics respectively. This computational work aims to quantify the amount of multiple light scattering detected by both the conventional Mie laser sheet imaging and the SLIPI technique. Results are compared for two hollow-cone fuel sprays of different transmission and droplet size properties. In the first spray the laser transmission, at λ = 532 nm, is 5% in the dense region and 27% in the dilute region, with a droplet size distribution ranging from 8 to 68 µm. The second spray is assumed to be more highly atomized, with a transmission of only 0.17% in the dense region and 7.5% in the dilute region, and with a droplets size distribution ranging from 4 to 34 µm. From these numerical calculations, it is observed that the resultant SLIPI signal tends to be closer from the pure single scattering signal when reducing the spatial period of the incident modulated light. We demonstrate here that the technique should be able to suppress an unwanted light contribution up to 91%, of the light intensity detected in the conventional planar imaging.
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