| 1. |
- 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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| 2. |
- Bao, Yupan
(författare)
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Development of optical diagnostics of plasma-related phenomena and applications
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Optical diagnostics techniques based on coded imaging were developed and applied for plasma-related phenomena and applications. The signal of interest is first encoded with a sinusoid pattern either by structured laser illumination or implement of a diffractive optical element, such as a grating, along the optical path of the signal. The coded signal will then be extracted from the raw data by a lock-in based algorithm, such as frequency recognition algorithm for multipleexposures (FRAME). Two types of non-thermal plasma sources, i.e., gliding arc discharges and nanosecond pulsed discharges, were investigated. Volumetric information of molecular distributions around a gliding arc was captured using laser-induced fluorescence with structured illumination and FRAME. Laser scattering imaging during the formation of a nanosecond pulsed discharge on a at methane-air flame was extracted from luminous plasma emission using structured laser illumination. Furthermore, a technique named periodic shadowing was applied for streak camera measurements, where both higher temporal contrast and effective dynamic range were achieved. The gliding arc plasma discharge was also applied in an industrial prototype burner as plasma-assisted combustion has been proven to be a promising technique to increase energy efficiency as well as reduce environmentally harmful emission. With the help of 0.1% additional energy, the lean blow-out limit of a hundred kilowatt burner was extended from a global equivalence ratio of 0.47 to 0.45.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- Kornienko, Vassily, et al.
(författare)
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Periodic Shadowing for Improved Temporal Resolution in Streak Cameras
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics, CLEO 2023. - 9781957171258
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Konferensbidrag (refereegranskat)abstract
- Streak cameras are central to measurements across the sciences. By spatially modulating the entrance slit, we show a more than 20% increase in temporal resolution opening up for sub-picosecond measurements with standard streak camera systems.
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| 7. |
- Kornienko, Vassily, et al.
(författare)
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The Space-Charge Problem in Ultrafast Diagnostics : An All-Optical Solution for Streak Cameras
- 2024
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Ingår i: Ultrafast Science. - 2097-0331. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The field of ultrafast science is dependent on either ultrashort laser pulse technology or ultrafast passive detection. While there exists a plethora of sub-picosecond laser pulse solutions, streak cameras are singular in providing sub-picosecond passive imaging capabilities. Therefore, their use in fields ranging from medicine to physics is prevalent. Streak cameras attain such temporal resolutions by converting signal photons to electrons. However, the Coulomb repulsion force spreads these electrons spatiotemporally aggravating streak cameras’ temporal resolution and dynamic range—an effect that increases in severity in ultrafast applications where electrons are generated nearly instantaneously. While many electro-optical solutions have been proposed and successfully implemented, this issue remains as a challenge for all subpicosecond streak camera technology. Instead of resorting to electro-optical solutions, in this work, we present an all-optical approach based on the combination of photon tagging and spatial lock-in detection with a technique called periodic shadowing—that is directly applicable to all generations of streak cameras. We have demonstrated that this accessible all-optical solution, consisting of a single externally applied optical component, results in (a) a >3× improvement in dynamic range, (b) a 25% increase in temporal resolution, and (c) a reduction of background noise levels by a factor of 50, which, when combined, allows for a markedly improved accuracy in the measurement of ultrafast signals.
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| 8. |
- Li, Qian, et al.
(författare)
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Slow-light-based optical frequency shifter
- 2016
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 93:4
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate experimentally and theoretically a controllable way of shifting the frequency of an optical pulse by using a combination of spectral hole burning, slow light effect, and linear Stark effect in a rare-earth-ion-doped crystal. We claim that the solid angle of acceptance of a frequency shift structure can be close to 2π, which means that the frequency shifter could work not only for optical pulses propagating in a specific spatial mode but also for randomly scattered light. As the frequency shift is controlled solely by an external electric field, it works also for weak coherent light fields and can be used, for example, as a frequency shifter for quantum memory devices in quantum communication.
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| 9. |
- Liu, Xin, et al.
(författare)
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Experimental Investigation of Plasma Discharge Effect on Swirl Flames at a Scaled Siemens Dry Low Emission Burner
- 2021
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Ingår i: AIAA Scitech 2021 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624106095
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Konferensbidrag (refereegranskat)abstract
- The effect of a Rotating Gliding Arc (RGA) plasma discharge on the flame in a scaled Siemens Dry Low Emission (DLE), SGT-750, burner was experimentally investigated under atmospheric combustion conditions. The central pilot section of the burner, named RPL (rich pilot lean), was redesigned with an integrated high voltage electrode to generate an RGA. The exhaust gas was sampled and analysed in terms of CO and NOx emissions, and the CO emission data show that the RGA extends the lean blow-out limit (LBO). High-speed OH chemiluminescence imaging was employed to understand the transient behaviour of the flame in both conditions with and without RGA and also to study the process of flame re-stabilization by the assistance of the RGA. A flame kernel, initiated around the RGA channel, was observed to play an important role in the re-stabilizing process of the flame. Although the NOx emission for the flame with RGA was found to be higher than that without RGA, it was still less than what previous data show for operating conditions with the RPL flame.
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| 10. |
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