| 1. |
- Marklund, Olov
(författare)
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Robust fringe density and direction estimation in noisy phase maps
- 2001
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Ingår i: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 18:11, s. 2717-2727
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Tidskriftsartikel (refereegranskat)abstract
- A method for automated fringe analysis is presented. It robustly estimates local fringe density and direction in noisy wrapped phase maps. Such information can be used to improve the performance of two-dimensional phase unwrapping methods, to construct phase-jump-preserving filtering strategies, and also to perform robust segmentation of phase data. The method, which is highly insensitive to noise, is model based and performs the estimation in the Fourier domain.
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| 2. |
- Réfrégier, P., et al.
(författare)
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Entropy of partially polarized light and application to statistical processing techniques
- 2004
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Ingår i: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 21:11, s. 2124-2134
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Tidskriftsartikel (refereegranskat)abstract
- We have analyzed entropy properties of coherent and partially polarized light in an arbitrary number of spatial dimensions. We show that for Gaussian fields, the Shannon entropy is a simple function of the intensity and of the Barakat degree of polarization. In particular, we provide a probabilistic interpretation of this definition of the degree of polarization. Using information theory results, we also deduce some physical properties of partially polarized light such as additivity of the entropy and depolarization effects induced by mixing partially polarized states of light. Finally, we demonstrate that entropy measures can play an important role in segmentation and detection tasks.
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| 3. |
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| 4. |
- Dai, Daoxin, et al.
(författare)
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Accurate two-dimensional model of an arrayed-waveguide grating demultiplexer and optimal design based on the reciprocity theory
- 2004
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Ingår i: Journal of the Optical Society of America A: Optics and Image Science, and Vision. - 1084-7529. ; 21:12, s. 2392-2398
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Tidskriftsartikel (refereegranskat)abstract
- An accurate two-dimensional (2D) model is introduced for the simulation of an arrayed-waveguide grating (AWG) demultiplexer by integrating the field distribution along the vertical direction. The equivalent 2D model has almost the same accuracy as the original three-dimensional model and is more accurate for the AWG considered here than the conventional 2D model based on the effective-index method. To further improve the computational efficiency, the reciprocity theory is applied to the optimal design of a flat-top AWG demultiplexer with a special input structure.
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| 5. |
- Gislén, Anna, et al.
(författare)
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On the optical theory of underwater vision in humans
- 2004
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Ingår i: Journal of the Optical Society of America A. - 1084-7529. ; 21:11, s. 2061-2064
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Tidskriftsartikel (refereegranskat)abstract
- Defocus changes the visual contrast sensitivity function, thereby creating a complex curve with local dips and peaks. Since underwater vision in humans is severely defocused, we used optical theory and the phenomenon of spurious resolution to predict how well humans can see in this environment. The values obtained correspond well with experimental measurements of underwater human acuity from earlier studies and even point to an opportunity for humans with exceptional contrast sensitivity to see better underwater than the children in those studies. The same theory could be useful when discussing the visual acuity of amphibious animals, as they may use pupil constriction as a means of improving underwater vision.
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| 6. |
- He, Jiangping, et al.
(författare)
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Light scattering by multiple red blood cells
- 2004
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Ingår i: Journal of the Optical Society of America A: Optics and Image Science, and Vision. - 1084-7529. ; 21:10, s. 1953-1961
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of light with multiple red blood cells was systematically investigated by the finite-difference time-domain method (FDTD). The simulations showed that the lateral multiple scattering between red blood cells is very weak and that the polarization has an almost insignificant influence on the distribution of the scattered light. The numerical results of the FDTD method were compared with the results from the Rytov approximation and the discrete dipole approximation (DDA). The agreement with the DDA was excellent.
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| 7. |
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| 8. |
- Owner-Petersen, Mette, et al.
(författare)
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Multiconjugate adaptive optics for large telescopes: analytical control of the mirror shapes
- 2002
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Ingår i: Journal of the Optical Society of America A. - 1084-7529. ; 19:3, s. 537-548
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Tidskriftsartikel (refereegranskat)abstract
- We present an analytical algorithm for deriving the shapes of the deformable mirrors to be used for multiconjugate adaptive correction on a large telescope. The algorithm is optimal in the limit where the overlap of the wave-front contributions from relevant atmospheric layers probed by the guide stars is close to the size of the pupil. The fundamental principle for correction is based on a minimization of the sum of the residual power spectra of the phase fluctuations seen by the guide stars after correction. On the basis of the expressions for the mirror shapes, so-called layer transfer functions describing the distribution of the correction of a single atmospheric layer among the deformable mirrors and the resulting correction of that layer have been derived. It is shown that for five guide stars distributed in a regular cross, two- and three-mirror correction will be possible only up to a maximum frequency defined by the largest separation of the conjugate altitudes of the mirrors and by the angular separation of the guide stars. The performance of the algorithm is investigated in the K band by using a standard seven-layer atmosphere. We present results obtained for two guide-star configurations: a continuous distribution within a given angular radius and a five-star cross pattern with a given angular arm length. The wave-front fluctuations are subjected to correction using one, two, and three deformable mirrors, The needed mirror dynamic range is derived as required root-mean-square stroke and actuator pitch. Finally the performance is estimated in terms of the Strehl ratio obtained by the correction as a function of field angle. No noise has been included in the present analysis, and the guide stars are assumed to be at infinity.
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| 9. |
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| 10. |
- Tervo, J., et al.
(författare)
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Theory of partially coherent electromagnetic fields in the space-frequency domain
- 2004
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Ingår i: Journal of the Optical Society of America a-Optics Image Science and Vision. - 1084-7529. ; 21:11, s. 2205-2215
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Tidskriftsartikel (refereegranskat)abstract
- We construct the coherent-mode representation for fluctuating, statistically stationary electromagnetic fields. The modes are shown to be spatially fully coherent in the sense of a recently introduced spectral degree of electromagnetic coherence. We also prove that the electric cross-spectral density tenser can be rigorously expressed as a correlation tenser averaged over an appropriate ensemble of strictly monochromatic vectorial wave functions. The formalism is demonstrated for partially polarized, partially coherent Gaussian Schell-model beams, but the theory applies to arbitrary random electromagnetic fields and can find applications in radiation and propagation and in inverse problems.
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