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Träfflista för sökning "L773:1094 4087 ;lar1:(miun)"

Sökning: L773:1094 4087 > Mittuniversitetet

  • Resultat 1-7 av 7
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1.
  • Engholm, Magnus, et al. (författare)
  • Preventing Photodarkening in Ytterbium-Doped High Power Fiber Lasers; Correlation to the UV-Transparency of the Core Glass
  • 2008
  • Ingår i: Optics Express. - 1094-4087. ; 16:2, s. 1260-1268
  • Tidskriftsartikel (refereegranskat)abstract
    •   Photodarkening experiments are performed on ytterbium-doped silicate glass samples. A strong charge-transfer (CT) absorption band near 230nm in aluminosilicate glass is found to be correlated to the mechanism of induced color center formation. Excitation into the CT-absorption band generates similar color centers as observed in ytterbium-doped fiber lasers under 915nm high power diode pumping. The position of the CT-absorption band is compositional dependent and is shifted to shorter wavelengths in ytterbium doped phosphosilicate glass. Very low levels of photodarkening is observed for the ytterbium doped phosphosilicate glass composition under 915nm high power diode pumping. Possible excitation routes to reach the CT-absorption band under 915nm pumping are discussed.  
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2.
  • Gustafsson Coppel, Ludovic, 1973-, et al. (författare)
  • Angular dependence of fluorescence from turbid media
  • 2015
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 23:15, s. 19552-19564
  • Tidskriftsartikel (refereegranskat)abstract
    • We perform Monte Carlo light scattering simulations to study the angular distribution of the fluorescence emission from turbid media and compare the results to measured angular distributions from fluorescing white paper samples. The angular distribution of fluorescence emission is significantly depending on the concentration of fluorophores. The simulations show also a dependence on the angle of incidence that is however not as evident in the measurements. A detailed analysis of the factors affecting this angular distribution indicates that it is strongly correlated to the mean depth of the fluorescence process. The findings can find applications in fluorescence spectroscopy and are of particular interest when optimizing the impact of fluorescence on e.g.the appearance of paper as the measured values are angle dependent.
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3.
  • Gustafsson Coppel, Ludovic, 1975-, et al. (författare)
  • Lateral light scattering in paper - MTF simulation and measurement
  • 2011
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 19:25, s. 25181-25187
  • Tidskriftsartikel (refereegranskat)abstract
    • The modulation transfer function (MTF) of 22 paper samples is computed using Monte Carlo simulations with isotropic or strongly forward single scattering. The inverse frequency at half maximum of the MTF (kp) is found inappropriate as a single metric for the MTF since it is insensitive to the shape of the modeled and simulated MTF. The single scattering phase function has a significant impact on the shape of the MTF, leading to more lateral scattering. However, anisotropic single scattering cannot explain the larger lateral scattering observed in paper. It is argued that the directional inhomogeneity of paper requires a light scattering model with both the phase function and scattering distances being dependent on the absolute direction.
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4.
  • Linder, Tomas, et al. (författare)
  • Lateral light scattering in fibrous media
  • 2013
  • Ingår i: Optics Express. - 1094-4087. ; 21:6, s. 7835-7840
  • Tidskriftsartikel (refereegranskat)abstract
    • Lateral light scattering in fibrous media is investigated by computing the modulation transfer function (MTF) of 22 paper samples using a Monte Carlo model. The simulation tool uses phase functions from infinitely long homogenous cylinders and the directional inhomogeneity of paper is achieved by aligning the cylinders in the plane. The inverse frequency at half maximum of the MTF is compared to both measurements and previous simulations with isotropic and strongly forward single scattering phase functions. It is found that the conical scattering by cylinders enhances the lateral scattering and therefore predicts a larger extent of lateral light scattering than models using rotationally invariant single scattering phase functions. However, it does not fully reach the levels of lateral scattering observed in measurements. It is argued that the hollow lumen of a wood fiber or dependent scattering effects must be considered for a complete description of lateral light scattering in paper.
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5.
  • Moon, Inkyu, et al. (författare)
  • Noise-free quantitative phase imaging in Gabor holography with conditional generative adversarial network
  • 2020
  • Ingår i: Optics Express. - 1094-4087. ; 28:18, s. 26284-26301
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper shows that deep learning can eliminate the superimposed twin-image noise in phase images of Gabor holographic setup. This is achieved by the conditional generative adversarial model (C-GAN), trained by input-output pairs of noisy phase images obtained from synthetic Gabor holography and the corresponding quantitative noise-free contrast-phase image obtained by the off-axis digital holography. To train the model, Gabor holograms are generated from digital off-axis holograms with spatial shifting of the real image and twin image in the frequency domain and then adding them with the DC term in the spatial domain. Finally, the digital propagation of the Gabor hologram with Fresnel approximation generates a super-imposed phase image for the C-GAN model input. Two models were trained: a human red blood cell model and an elliptical cancer cell model. Following the training, several quantitative analyses were conducted on the bio-chemical properties and similarity between actual noise-free phase images and the model output. Surprisingly, it is discovered that our model can recover other elliptical cell lines that were not observed during the training. Additionally, some misalignments can also be compensated with the trained model. Particularly, if the reconstruction distance is somewhat incorrect, this model can still retrieve in-focus images. 
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6.
  • Neuman, Magnus, et al. (författare)
  • Point spreading in turbid media with anisotropic single scattering
  • 2011
  • Ingår i: Optics Express. - : OSA. - 1094-4087. ; 19:3, s. 1915-1920
  • Tidskriftsartikel (refereegranskat)abstract
    • Point spreading is investigated using general radiative transfer theory. We find that the single scattering anisotropy plays a significant role for point spreading together with the medium mean free path, single scattering albedo and thickness. When forward scattering dominates, the light will on average undergo more scattering events to give a specific optical response in reflectance measurements. This will significantly increase point spreading if the medium is low absorbing with large mean free path. Any fundamental and generic model of point spreading must capture the dependence on all of these medium characteristics.
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7.
  • Rydberg, Sara, et al. (författare)
  • Experimental evidence for the formation of divalent Ytterbium in the photodarkening process of Yb-doped fiber lasers
  • 2013
  • Ingår i: Optics Express. - 1094-4087. ; 21:6, s. 6681-6688
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we present experimental evidence that the valence instability of the ytterbium ion play a key role for the observed photodarkening mechanism in Yb-doped fiber lasers. Luminescence and excitation spectroscopy performed on UV irradiated Yb/Al doped silica glass preforms and near-infrared diode pumped photodarkened fibers show a concentration increase of Yb2+ ions. A concentration decrease in Yb3+ could also be observed for the UV irradiated preform. The findings contribute to an increased understanding of the kinetic processes related to photodarkening in Yb-doped high power fiber lasers.
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  • Resultat 1-7 av 7

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