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Sökning: L773:1094 4087

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51.
  • Bellucci, Valerio, et al. (författare)
  • Hard X-ray stereographic microscopy for single-shot differential phase imaging
  • 2023
  • Ingår i: Optics Express. - 1094-4087. ; 31:11, s. 18399-18406
  • Tidskriftsartikel (refereegranskat)abstract
    • The characterisation of fast phenomena at the microscopic scale is required for the understanding of catastrophic responses of materials to loads and shocks, the processing of materials by optical or mechanical means, the processes involved in many key technologies such as additive manufacturing and microfluidics, and the mixing of fuels in combustion. Such processes are usually stochastic in nature and occur within the opaque interior volumes of materials or samples, with complex dynamics that evolve in all three dimensions at speeds exceeding many meters per second. There is therefore a need for the ability to record three-dimensional X-ray movies of irreversible processes with resolutions of micrometers and frame rates of microseconds. Here we demonstrate a method to achieve this by recording a stereo phase-contrast image pair in a single exposure. The two images are combined computationally to reconstruct a 3D model of the object. The method is extendable to more than two simultaneous views. When combined with megahertz pulse trains of X-ray free-electron lasers (XFELs) it will be possible to create movies able to resolve 3D trajectories with velocities of kilometers per second.
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52.
  • Belonovski, Alexey V, et al. (författare)
  • Quantum analysis of luminescence of an exciton in a meso-cavity
  • 2021
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 29:13, s. 20724-20734
  • Tidskriftsartikel (refereegranskat)abstract
    • Interaction of cavity modes with an exciton in a meso-cavity (the structure supporting several cavity modes separated by an energy interval comparable to Rabi-splitting of an exciton and cavity modes) has been analyzed using a quantum-mechanical approach. Simultaneous interaction of an exciton and several cavity modes results in few novel effects such as ladder-like increase of the exciton population in the system, quantum beating and non-monotonic dependence of the ground polariton state in the system on the pumping. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.
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53.
  • Belonovski, Alexey V, et al. (författare)
  • Weak and strong coupling of photons and excitons in planar meso-cavities
  • 2020
  • Ingår i: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 28:9, s. 12688-12698
  • Tidskriftsartikel (refereegranskat)abstract
    • The interaction of an exciton and cavity modes is considered in planar meso-cavities, which have lateral sizes corresponding to few wavelengths. In meso-cavities, the frequency interval between the optical modes is comparable or smaller than the value of the Rabi splitting between the exciton and the optical modes. The Hamiltonian of the interaction between the exciton and the cavity modes is constructed, and it is shown that such an interaction between the cavity modes and the exciton can occur both in weak and in strong coupling regimes. The latter case can be accompanied by a pronounced splitting of the emission peaks as shown for modelled meso-cavities of triangular, square and hexagonal shapes, where it is demonstrated that Q-factors for the adjacent cavity modes as well as the strength of interaction with excitons can differ by few orders of magnitude. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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54.
  • Bergstrand, Jan, et al. (författare)
  • Scanning inverse fluorescence correlation spectroscopy
  • 2014
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 22:11, s. 13073-13090
  • Tidskriftsartikel (refereegranskat)abstract
    • Scanning Inverse Fluorescence Correlation Spectroscopy (siFCS) is introduced to determine the absolute size of nanodomains on surfaces. We describe here equations for obtaining the domain size from cross-and auto-correlation functions, measurement simulations which enabled testing of these equations, and measurements on model surfaces mimicking membranes containing nanodomains. Using a confocal microscope of 270 nm resolution the size of 250 nm domains were estimated by siFCS to 257 +/- 12 nm diameter, and 40 nm domains were estimated to 65 +/- 26 nm diameter. Applications of siFCS for sizing of nanodomains and protein clusters in cell membranes are discussed.
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55.
  • Berrocal, Edouard, et al. (författare)
  • Application of structured illumination for multiple scattering suppression in planar laser imaging of dense sprays.
  • 2008
  • Ingår i: Optics Express. - 1094-4087. ; 16:22, s. 17870-17881
  • 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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56.
  • Berrocal, Edouard, et al. (författare)
  • Laser light scattering in turbid media part I: Experimental and simulated results for the spatial intensity distribution
  • 2007
  • Ingår i: Optics Express. - 1094-4087. ; 15:17, s. 10649-10665
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the scattering and multiple scattering of a typical laser beam (lambda= 800 nm) in the intermediate scattering regime. The turbid media used in this work are homogeneous solutions of monodisperse polystyrene spheres in distilled water. The two-dimensional distribution of light intensity is recorded experimentally, and calculated via Monte Carlo simulation for both forward and side scattering. The contribution of each scattering order to the total detected light intensity is quantified for a range of different scattering phase functions, optical depths, and detection acceptance angles. The Lorentz-Mie scattering phase function for individual particles is varied by using different sphere diameters (D = 1 and 5 mu m). The optical depth of the turbid medium is varied (OD = 2, 5, and 10) by employing different concentrations of polystyrene spheres. Detection angles of theta(a) = 1.5 and 8.5 are considered. A novel approach which realistically models the experimental laser source is employed in this paper, and very good agreement between the experimental and simulated results is demonstrated. The data presented here can be of use to validate other modern Monte Carlo models, which generate high resolution light intensity distributions. Finally, an extrapolation of the Beer-Lambert law to multiple scattering is proposed based on the Monte Carlo calculation of the ballistic photon contribution to the total detected light intensity.
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57.
  • Berrocal, Edouard, et al. (författare)
  • Laser light scattering in turbid media Part II: Spatial and temporal analysis of individual scattering orders via Monte Carlo simulation.
  • 2009
  • Ingår i: Optics Express. - 1094-4087. ; 17:16, s. 13792-13809
  • Tidskriftsartikel (refereegranskat)abstract
    • In Part I of this study [1], good agreement between experimental measurements and results from Monte Carlo simulations were obtained for the spatial intensity distribution of a laser beam propagating within a turbid environment. In this second part, the validated Monte Carlo model is used to investigate spatial and temporal effects from distinct scattering orders on image formation. The contribution of ballistic photons and the first twelve scattering orders are analyzed individually by filtering the appropriate data from simulation results. Side-scattering and forward-scattering detection geometries are investigated and compared. We demonstrate that the distribution of positions for the final scattering events is independent of particle concentration when considering a given scattering order in forward detection. From this observation, it follows that the normalized intensity distribution of each order, in both space and time, is independent of the number density of particles. As a result, the amount of transmitted information is constant for a given scattering order and is directly related to the phase function in association with the detection acceptance angle. Finally, a contrast analysis is performed in order to quantify this information at the image plane.
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58.
  • Bertani, Stefano, et al. (författare)
  • Stretching-tunable external-cavity laser locked by an elastic silicone grating
  • 2006
  • Ingår i: Optics Express. - 1094-4087. ; 14:25, s. 11982-11986
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate wavelength locking of a diode laser at 760 nm with feedback from an elastic transmission grating in the Littrow configuration. The laser was in a single longitudinal mode with a side-mode suppression of 20 dB. By stretching the grating the laser could be tuned over a few nm. The grating was fabricated in a silicone elastomer ( polydimethylsiloxane) by a moulding technique, and coated by a thin layer of Ti and Au to achieve an increased diffraction efficiency needed for efficient locking.
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59.
  • Bertilson, Michael, et al. (författare)
  • High-resolution computed tomography with a compact soft x-ray microscope
  • 2009
  • Ingår i: Optics Express. - 1094-4087. ; 17:13, s. 11057-11065
  • Tidskriftsartikel (refereegranskat)abstract
    • Computed tomography based on high-resolution soft x-ray microscopy utilizes the natural contrast for biological specimens provided by the water window (lambda = 2.4 - 4.4 nm) and the high resolving power of zone plate objectives. It is capable of revealing the 3D structure of biological specimens at sub-visible-microscopic resolution. To date, the technique has only been available at synchrotron-based microscopes, which limits the researchers access. In the present paper we demonstrate high-resolution soft x-ray tomography with a laboratory zone-plate-based soft x-ray microscope. The specimen, a diatom mounted on a glass capillary, was reconstructed from a tilt series of 53 images covering 180 using a filtered back projection algorithm. The resolution of the tomogram was estimated to a half period of 140 nm using a differential-phase-residual method. Cryo-fixation, increased source brightness and extended-depth-of-focus objectives are important for pushing the resolution of compact systems for biological samples.
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60.
  • Bertilson, Michael, et al. (författare)
  • Numerical model for tomographic image formation in transmission x-ray microscopy
  • 2011
  • Ingår i: Optics Express. - 1094-4087. ; 19:12, s. 11578-11583
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a numerical image-formation model for investigating the influence of partial coherence, sample thickness and depth-of-focus on the accuracy of tomographic reconstructions in transmission x-ray microscopes. The model combines wave propagation through the object by finite difference techniques with Fourier methods. We include a ray-tracing model to analyse the origin of detrimental stray light in zone plate-based x-ray microscopes. These models allow optimization of x-ray microscopy systems for quantitative tomographic imaging of thick objects. Results show that both the depth-of-focus and the reconstructed local absorption coefficient are highly dependent on the degree of coherence of the optical system.
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