| 1. |
- Cai, Yangjian, et al.
(författare)
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Coincidence subwavelength fractional Fourier transform
- 2006
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Ingår i: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 23:4, s. 835-841
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Tidskriftsartikel (refereegranskat)abstract
- The coincidence subwavelength fractional Fourier transforms (FRTs) with entangled photon pairs and incoherent light radiation are introduced as an extension of the recently introduced coincidence FRT. Optical systems for implementing the coincidence subwavelength FRTs are designed. The width of the coincidence subwavelength FRT pattern is two times narrower than the width of the coincidence FRT. The coincidence subwavelength FRT with partially coherent light radiation is also studied numerically. Differences between the coincidence subwavelength FRT with entangled photon pairs and that with incoherent light radiation are discussed.
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| 2. |
- Calander, Nils, 1953
(författare)
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Focused optical beams obtained at planar structures by an imaginary shift in position
- 2007
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Ingår i: Journal of the Optical Society of America A: Optics and Image Science, and Vision. - 1084-7529 .- 1520-8532. ; 24:9, s. 2513-2515
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Tidskriftsartikel (refereegranskat)abstract
- A theory for focused optical beams at planar structures is described. It is an extension of a previous theory based on summation of plane waves. The focused beam is obtained by an imaginary shift in the position vector of the plane waves. It is well suited for calculations of electromagnetic fields at planar surface plasmon resonance structures excited by a focused optical beam.
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| 3. |
- Hällstig, Emil, et al.
(författare)
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Polarization properties of a nematic liquid-crystal spatial light modulator for phase modulation
- 2005
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Ingår i: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 22:1, s. 177-184
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Tidskriftsartikel (refereegranskat)abstract
- The polarization properties of a nematic zero-twist liquid-crystal (NLC) spatial light modulator (SLM) were studied. A large ratio between the liquid-crystal (LC) layer thickness and the pixel pitch combined with spatial variations in the applied electric field causes fringing fields between pixels. Depending on the LC alignment, the electric field components within the LC layer can result in a twist deformation. The produced inhomogeneous optical anisotropy affects the polarization of light propagating through the device. We experimentally examined polarization effects in different diffraction orders for both binary and blazed phase gratings. Simulations of the LC deformation together with finite-difference time-domain simulations for the optical propagation were used to calculate the corresponding far-field intensities. It was demonstrated how rigorous simulations of the NLC SLM properties can be used to understand the polarization features of different diffraction orders.
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| 4. |
- Lenz, R, et al.
(författare)
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Statistical properties of color-signal spaces
- 2005
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Ingår i: Journal of the Optical Society of America. A, Optics, image science, and vision. - : The Optical Society. - 1084-7529 .- 1520-8532. ; 22:5, s. 820-827
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Tidskriftsartikel (refereegranskat)
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| 5. |
- Lundström, Linda, et al.
(författare)
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Population distribution of wavefront aberrations in the peripheral human eye
- 2009
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Ingår i: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 26:10, s. 2192-2198
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Tidskriftsartikel (refereegranskat)abstract
- We present a population study of peripheral wavefront aberrations in large off-axis angles in terms of Zernike coefficients. A laboratory Hartmann-Shack sensor was used to assess the aberrations in 0 degrees, 20 degrees, and 30 degrees in the nasal visual field of 43 normal eyes. The elliptical pupil meant that the quantification could be done in different ways. The three approaches used were (1) over a circular aperture encircling the pupil, (2) over a stretched version of the elliptical pupil, and (3) over a circular aperture within the pupil (MATLAB conversion code given). Astigmatism (c(2)(2)) increased quadratically and coma (c(3)(1)) linearly with the horizontal viewing angle, whereas spherical aberration (c(4)(0)) decreased slightly toward the periphery. There was no correlation between defocus and angle, although some trends were found when the subjects were divided into groups depending on refractive error. When comparing results of different studies it has to be kept in mind that the coefficients differ depending on how the elliptical pupil is taken into consideration.
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| 6. |
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| 7. |
- Saager, Rolf B., 1974-, et al.
(författare)
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Direct characterization and removal of interfering absorption trends in two-layer turbid media
- 2005
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Ingår i: Journal of the Optical Society of America A. - : OSA Publishing. - 0740-3232 .- 1084-7529 .- 1520-8532. ; 22:9, s. 1874-882
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Tidskriftsartikel (refereegranskat)abstract
- We propose a method to isolate absorption trends confined to the lower layer of a two-layer turbid medium, as is desired in near-infrared spectroscopy (NIRS) of cerebral hemodynamics. Several two-layer Monte Carlo simulations of NIRS time series were generated using a physiologically relevant range of optical properties and varying the absorption coefficients due to bottom-layer, top-layer, and/or global fluctuations. Initial results showed that by measuring absorption trends at two source–detector separations and performing a least-squares fit of one to the other, processed signals strongly resemble the simulated bottom-layer absorption properties. Through this approach, it was demonstrated that fitting coefficients can be estimated within less than ±2% of the ideal value without any a priori knowledge of the optical properties present in the model. An analytical approximation for the least-squares coefficient provides physical insight into the nature of errors and suggests ways to reduce them.
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| 8. |
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| 9. |
- Alsam, Ali, et al.
(författare)
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Calibrating color cameras using metameric blacks
- 2007
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Ingår i: Journal of the Optical Society of America A: Optics and Image Science, and Vision. - 1084-7529. ; 24:1, s. 11-17
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Tidskriftsartikel (refereegranskat)abstract
- Spectral calibration of digital cameras based on the spectral data of commercially available calibration charts is an ill-conditioned problem that has an infinite number of solutions. We introduce a method to estimate the sensor's spectral sensitivity function based on metamers. For a given patch on the calibration chart we construct numerical metamers by computing convex linear combinations of spectra from calibration chips with lower and higher sensor response values. The difference between the measured reflectance spectrum and the numerical metamer lies in the null space of the sensor. For each measured spectrum we use this procedure to compute a collection of color signals that lie in the null space of the sensor. For a collection of such spaces we compute the robust principal components, and we obtain an estimate of the sensor by computing the common null space spanned by these vectors. Our approach has a number of advantages over standard techniques: It is robust to outliers and is not dominated by larger response values, and it offers the ability to evaluate the goodness of the solution where it is possible to show that the solution is optimal, given the data, if the calculated range is one dimensional. © 2006 Optical Society of America.
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| 10. |
- Cai, Yangjian, et al.
(författare)
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Coincidence fractional Fourier transform implemented with partially coherent light radiation
- 2005
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Ingår i: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION. - 1084-7529. ; 22:9, s. 1798-1804
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Tidskriftsartikel (refereegranskat)abstract
- We introduce the coincidence fractional Fourier transform (FRT) implemented with incoherent and partially coherent light radiation. Optical systems for implementing the coincidence FRT are designed. The results show that the visibility and quality of the coincidence FRT of an object are closely related to the light source's transverse size, coherence, and spectral width. As an example, we numerically study the coincidence FRT of a single slit. (c) 2005 Optical Society of America.
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