| 1. |
- Berrocal, Edouard, et al.
(författare)
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Application of structured illumination for multiple scattering suppression in planar laser imaging of dense sprays.
- 2008
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Ingår i: Optics Express. - 1094-4087. ; 16:22, s. 17870-17881
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Tidskriftsartikel (refereegranskat)abstract
- A novel approach to reduce the multiple light scattering contribution in planar laser images of atomizing sprays is reported. This new technique, named Structured Laser Illumination Planar Imaging (SLIPI), has been demonstrated in the dense region of a hollow-cone water spray generated in ambient air at 50 bars injection pressure. The idea is based on using an incident laser sheet which is spatially modulated along the vertical direction. By properly shifting the spatial phase of the modulation and using post-processing of the successive recorded images, the blurring effects from multiple light scattering can be mitigated. Since hollow-cone sprays have a known inner structure in the central region, the efficiency of the method could be evaluated. We demonstrate, for the case of averaged images, that an unwanted contribution of 44% of the detected light intensity can be removed. The suppression of this diffuse light enables an increase from 55% to 80% in image contrast. Such an improvement allows a more accurate description of the near-field region and of the spray interior. The possibility of extracting instantaneous flow motion is also shown, here, for a dilute flow of water droplets. These results indicate promising applications of the technique to denser two-phase flows such as air-blast atomizer and diesel sprays.
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| 2. |
- Dorozynska, Karolina, et al.
(författare)
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A versatile, low-cost, snapshot multidimensional imaging approach based on structured light
- 2020
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Ingår i: Optics Express. - 1094-4087. ; 28:7, s. 9572-9586
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Tidskriftsartikel (refereegranskat)abstract
- The behaviour and function of dynamic samples can be investigated using optical imaging approaches with high temporal resolution and multidimensional acquisition. Snapshot techniques have been developed in order to meet these demands, however they are often designed to study a specific parameter, such as spectral properties, limiting their applicability. Here we present and demonstrate a frequency recognition algorithm for multiple exposures (FRAME) snapshot imaging approach, which can be reconfigured to capture polarization, temporal, depthof- focus and spectral information by simply changing the filters used. FRAME is implemented by splitting the emitted light from a sample into four channels, filtering the light and then applying a unique spatial modulation encoding before recombining all the channels. The multiplexed information is collected in a single exposure using a single detector and extracted in post processing of the Fourier transform of the collected image, where each channel image is located in a distinct region of the Fourier domain. The approach allows for individual intensity control in each channel, has easily interchangeable filters and can be used in conjunction with, in principle, all 2D detectors, making it a low cost and versatile snapshot multidimensional imaging technique.
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| 3. |
- Dorozynska, Karolina, et al.
(författare)
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Implementation of a multiplexed structured illumination method to achieve snapshot multispectral imaging
- 2017
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Ingår i: Optics Express. - 1094-4087. ; 25:15, s. 17211-17226
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Tidskriftsartikel (refereegranskat)abstract
- An instantaneous multispectral imaging setup based on frequency recognition algorithm for multiple exposures (FRAME) is presented and demonstrated experimentally. With this implementation of FRAME, each light source is uniquely encoded with a spatial modulation and the corresponding fluorescent responses pertaining to each maintain the same unique encoding. This allows the extraction of each source response from a single captured image by filtering in the Fourier domain. As a result, a multispectral imaging system based on FRAME can perform all the illumination and corresponding fluorescence detection simultaneously, where the latter is recorded in a single exposure and on a single detector and is thus capable of recording true ‘snapshot’ multispectral images. The results presented here demonstrate that the technique is capable of distinguishing source responses for well separated and co-localized fluorophores as well as providing z-sectioning capabilities. This implementation of FRAME demonstrates its viability as a tool for multispectral imaging of dynamic samples. Additionally, since all the spectral images are captured simultaneously, the method has potential for studying samples prone to photobleaching. Finally, this application of FRAME makes it possible to discriminate between signals due to infinitely spectrally close sources which, to the best of the authors’ knowledge, has not been possible in snapshot multispectral imaging schemes before.
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| 4. |
- Gong, Miaoxin, et al.
(författare)
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Fiber-based stray light suppression in spectroscopy using periodic shadowing
- 2021
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Ingår i: Optics Express. - 1094-4087. ; 29:5, s. 7232-7246
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Tidskriftsartikel (refereegranskat)abstract
- Stray light is a known strong interference in spectroscopic measurements. Photons from high-intensity signals that are scattered inside the spectrometer, or photons that enter the detector through unintended ways, will be added to the spectrum as an interference signal. A general experimental solution to this problem is presented here by introducing a customized fiber for signal collection. The fiber-mount to the spectrometer consists of a periodically arranged fiber array that, combined with lock-in analysis of the data, is capable of suppressing stray light for improved spectroscopy. The method, which is referred to as fiber-based periodic shadowing, was applied to Raman spectroscopy in combustion. The fiber-based stray-light suppression method is implemented in an experimental setup with a high-power high-repetition-rate laser system used for Raman measurements in different room-temperature gas mixtures and a premixed flame. It is shown that the stray-light level is reduced by up to a factor of 80. Weak spectral lines can be distinguished, and therefore better molecular species identification, as well as concentration and temperature evaluation, were performed. The results show that the method is feasible and efficient in practical use and that it can be employed as a general tool for improving spectroscopic accuracy.
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| 5. |
- Kristensson, Elias, et al.
(författare)
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Analysis of multiple scattering suppression using structured laser illumination planar imaging in scattering and fluorescing media
- 2011
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:14, s. 13647-13663
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Tidskriftsartikel (refereegranskat)abstract
- The accuracy, precision and limitations of the imaging technique named Structured Laser Illumination Planar Imaging (SLIPI) have been investigated. SLIPI, which allows multiply scattered light to be diminished, has previously demonstrated improvements in image quality and contrast for spray imaging. In the current study the method is applied to a controlled confined environment consisting of a mixture of water and monodisperse polystyrene microspheres. Elastic scattering and fluorescence are studied and the results obtained when probing different particle concentrations and diameters conclusively show the advantages of SLIPI for imaging within moderately turbid media. Although the technique presents both good repeatability and agreement with the Beer-Lambert law, discrepancies in its performance were, however, discovered. Photons undergoing scattering without changing their incident trajectory cannot be discriminated and, owing to differences in scattering phase functions, probing larger particles reduces the suppression of multiply scattered light. However, in terms of visibility such behavior is beneficial as it allows denser media to be probed. It is further demonstrated that the suppression of diffuse light performs equally well regardless of whether photons propagate along the incident direction or towards the camera. In addition, this filtering process acts independently on the spatial distribution of the multiply scattered light but is limited by the finite dynamic range and unavoidable signal noise of the camera.
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| 6. |
- Kristensson, Elias, et al.
(författare)
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High dynamic spectroscopy using a digital micromirror device and periodic shadowing
- 2017
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Ingår i: Optics Express. - 1094-4087. ; 25:1, s. 212-222
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Tidskriftsartikel (refereegranskat)abstract
- We present an optical solution called DMD-PS to boost the dynamic range of 2D imaging spectroscopic measurements up to 22 bits by incorporating a digital micromirror device (DMD) prior to detection in combination with the periodic shadowing (PS) approach. In contrast to high dynamic range (HDR), where the dynamic range is increased by recording several images at different exposure times, the current approach has the potential of improving the dynamic range from a single exposure and without saturation of the CCD sensor. In the procedure, the spectrum is imaged onto the DMD that selectively reduces the reflection from the intense spectral lines, allowing the signal from the weaker lines to be increased by a factor of 28 via longer exposure times, higher camera gains or increased laser power. This manipulation of the spectrum can either be based on a priori knowledge of the spectrum or by first performing a calibration measurement to sense the intensity distribution. The resulting benefits in detection sensitivity come, however, at the cost of strong generation of interfering stray light. To solve this issue the Periodic Shadowing technique, which is based on spatial light modulation, is also employed. In this proof-of-concept article we describe the full methodology of DMD-PS and demonstrate - using the calibration-based concept - an improvement in dynamic range by a factor of ∼100 over conventional imaging spectroscopy. The dynamic range of the presented approach will directly benefit from future technological development of DMDs and camera sensors.
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| 7. |
- Kristensson, Elias, et al.
(författare)
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Quantitative 3D imaging of scattering media using structured illumination and computed tomography
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:13, s. 14437-14450
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Tidskriftsartikel (refereegranskat)abstract
- An imaging technique capable of measuring the extinction coefficient in 3D is presented and demonstrated on various scattering media. The approach is able to suppress unwanted effects due to both multiple scattering and light extinction, which, in turbid situations, seriously hampers the performance of conventional imaging techniques. The main concept consists in illuminating the sample of interest with a light source that is spatially modulated in both the vertical and horizontal direction and to measure, using Structured Illumination, the correct transmission in 2D at several viewing angles. The sample is then reconstructed in 3D by means of a standard Computed Tomography algorithm. To create the adequate illumination, a novel "crossed" structured illumination approach is implemented. In this article, the accuracy and limitation of the method is first evaluated by probing several homogeneous milk solutions at various levels of turbidity. The unique possibility of visualizing an object hidden within such solutions is also demonstrated. Finally the method is applied on two different inhomogeneous scattering spray systems; one transient and one quasi-steady state. (C) 2012 Optical Society of America
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| 8. |
- Kristensson, Elias, et al.
(författare)
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Stray light suppression in spectroscopy using periodic shadowing
- 2014
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Ingår i: Optics Express. - 1094-4087. ; 22:7, s. 7711-7721
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that spectroscopic measurements suffer from an interference known as stray light, causing spectral distortion that reduces measurement accuracy. In severe situations, stray light may even obscure the existence of spectral lines. Here a novel general method is presented, named Periodic Shadowing, that enables effective stray light elimination in spectroscopy and experimental results are provided to demonstrate its capabilities and versatility. Besides its efficiency, implementing it in a spectroscopic arrangement comes at virtually no added experimental complexity. (C) 2014 Optical Society of America
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| 9. |
- Kristensson, Elias, et al.
(författare)
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Stray light suppression in spectroscopy using periodic shadowing
- 2014
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Ingår i: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 22:7, s. 7711-7711
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that spectroscopic measurements suffer from an interference known as stray light, causing spectral distortion that reduces measurement accuracy. In severe situations, stray light may even obscure the existence of spectral lines. Here a novel general method is presented, named Periodic Shadowing, that enables effective stray light elimination in spectroscopy and experimental results are provided to demonstrate its capabilities and versatility. Besides its efficiency, implementing it in a spectroscopic arrangement comes at virtually no added experimental complexity.
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| 10. |
- Mishra, Yogeshwar, et al.
(författare)
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Reliable LIF/Mie droplet sizing in sprays using structured laser illumination planar imaging
- 2014
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Ingår i: Optics Express. - 1094-4087. ; 22:4, s. 4480-4492
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In this article, Structured Laser Illumination Planar Imaging (SLIPI) is used in combination with the LIF/Mie ratio technique for extracting a reliable two-dimensional mapping of the droplets Sauter Mean Diameter (SMD). We show that even for the case of a fairly dilute spray, where single scattering events are in majority, the conventional LIF/Mie technique still remains largely affected by errors introduced by multiple light scattering. To remove this unwanted light intensity on both the LIF and Mie images SLIPI is used prior to apply the image ratio. For the first time, the SLIPI LIF/Mie results are calibrated and compared with measurement data from Phase Doppler Interferometry (PDI).
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