| 1. |
- Ekberg, Peter, et al.
(author)
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Fast and accurate metrology of multi-layered ceramic materials by an automated boundary detection algorithm developed for optical coherence tomography data
- 2014
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In: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 31:2, s. 217-226
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Journal article (peer-reviewed)abstract
- Optical coherence tomography (OCT) is useful for materials defect analysis and inspection with the additional possibility of quantitative dimensional metrology. Here, we present an automated image-processing algorithm for OCT analysis of roll-to-roll multilayers in 3D manufacturing of advanced ceramics. It has the advantage of avoiding filtering and preset modeling, and will, thus, introduce a simplification. The algorithm is validated for its capability of measuring the thickness of ceramic layers, extracting the boundaries of embedded features with irregular shapes, and detecting the geometric deformations. The accuracy of the algorithm is very high, and the reliability is better than 1 mu m when evaluating with the OCT images using the same gauge block step height reference. The method may be suitable for industrial applications to the rapid inspection of manufactured samples with high accuracy and robustness.
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| 2. |
- Freitag, Fabio Batista, et al.
(author)
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Effect of luminosity on color discrimination of dichromatic marmosets (Callithrix jacchus)
- 2012
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In: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 29:2, s. A216-22
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Journal article (peer-reviewed)abstract
- Psychophysical data have shown that under mesopic conditions cones and rods can interact, improving color vision. Since electrophysiological data have suggested that rods of dichromatic marmosets appear to be active at higher luminance, we aimed to investigate the effect of different levels of sunlight on the foraging abilities of male dichromatic marmosets. Captive marmosets were observed under three different conditions, with respect to their performance in detecting colored food items against a green background. Compared to high and low light intensities, intermediate luminosities significantly increased detection of orange targets by male dichromats, an indication of rod intrusion.
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| 3. |
- Gustafsson Coppel, Ludovic, 1975-, et al.
(author)
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Extension of the Stokes equation for layered constructions to fluorescent turbid media
- 2012
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In: Journal of the Optical Society of America A. - : Optical Society of America. - 1084-7529 .- 1520-8532. ; 29:4, s. 574-578
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Journal article (peer-reviewed)abstract
- Expressions relating the bispectral reflectance of a stack of n fluorescinglayers to each individual layer's reflectance and transmittance arederived. This theoretical framework is used together with recentlyproposed extensions of the Kubelka--Munk model to study the fluorescencefrom layered turbid media. For one layer over a reflecting background,the model is shown to give the same results as a previous model.The extension to n layers with different optical properties allowssimulating the bispectral reflectance from a pad of layered turbidmedia. The applicability of the model is exemplified with an optimizationof fluorophore distribution in layered turbid media.
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| 4. |
- Jaeken, Bart, et al.
(author)
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Peripheral aberrations in the human eye for different wavelengths : off-axis chromatic aberration
- 2011
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In: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 28:9, s. 1871-1879
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Journal article (peer-reviewed)abstract
- The interest in the eye's off-axis aberrations has increased strongly. On-axis the conversion of the aberration magnitude between different wavelengths is well known. We verified if this compensation is correct also for off-axis measurements by building a wavelength tunable peripheral Hartmann-Shack sensor and measuring 11 subjects out to +/- 30 degrees in the horizontal visual field. At the fovea, an average longitudinal chromatic aberration of 1D between red (671 nm) and blue (473 nm) light was found, and it increased slightly with eccentricity (up to 1.2D). A similar trend was measured for astigmatism as a function of wavelength (increase similar to 0.15D). Computational ray tracing in model eyes showed that the origin of the small increase of chromatic aberrations with eccentricity is the change of the oblique power of the refractive surfaces in the eye. Factors related to increase of axial length and refractive index of the eye were found to have a very small influence.
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| 5. |
- Kellock, Henri, et al.
(author)
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Image quality in double- and triple-intensity ghost imaging with classical partially polarized light
- 2012
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In: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 29:11, s. 2459-2468
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Journal article (peer-reviewed)abstract
- Classical ghost imaging is a correlation-imaging technique in which the image of the object is found through intensity correlations of light. We analyze three different quality parameters, namely the visibility, the signal-to-noise ratio (SNR), and the contrast-to-noise ratio (CNR), to assess the performance of double-and triple-intensity correlation-imaging setups. The source is a random partially polarized beam of light obeying Gaussian statistics, and the image quality is evaluated as a function of the degree of polarization (DoP). We show that the visibility improves when the DoP and the order of imaging increase, while the SNR behaves oppositely. The CNR is for the most part independent of DoP and the imaging order. The results are important for the development of new imaging devices using partially polarized light.
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| 6. |
- Neuman, Magnus, 1979-, et al.
(author)
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Anisotropic reflectance from turbid media. II. Measurements
- 2010
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In: Journal of the Optical Society of America A. - : The Optical Society. - 0740-3232 .- 1084-7529 .- 1520-8532. ; 27:5, s. 1040-1045
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Journal article (peer-reviewed)abstract
- The anisotropic reflectance from turbid media predicted using the radiative transfer based DORT2002 model is experimentally verified through goniophotometric measurements. A set of paper samples with varying amount of dye and thickness is prepared and their angle resolved reflectance is measured. An alleged perfect diffusor is also included. The corresponding simulations are performed. A complete agreement between the measurements and model predictions is seen regarding the characteristics of the anisotropy. They show that relatively more light is reflected in large polar angles when the absorption or illumination angle is increased or when the medium thickness is decreased. This is due to the relative amount of near-surface bulk scattering increasing in these cases. This affects the application of the Kubelka-Munk model as well as standards for reflectance measurements and calibration routines.
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| 7. |
- Ozcelikkale, Ayca, 1982, et al.
(author)
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Beyond Nyquist sampling: A cost-based approach
- 2013
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In: Journal of the Optical Society of America A: Optics and Image Science, and Vision. - 1084-7529 .- 1520-8532. ; 30:4, s. 645-655
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Journal article (peer-reviewed)abstract
- A sampling-based framework for finding the optimal representation of a finite energy optical field using a finite number of bits is presented. For a given bit budget, we determine the optimum number and spacing of the samples in order to represent the field with as low error as possible. We present the associated performance bounds as trade-off curves between the error and the cost budget. In contrast to common practice, which often treats sampling and quantization separately, we explicitly focus on the interplay between limited spatial resolution and limited amplitude accuracy, such as whether it is better to take more samples with lower amplitude accuracy or fewer samples with higher accuracy. We illustrate that in certain cases sampling at rates different from the Nyquist rate is more efficient. © 2013 Optical Society of America.
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| 8. |
- Shabbir, Saroosh, et al.
(author)
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Arbitrary interference curves by coincidence detection : Theory and experiment
- 2013
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In: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 30:10, s. 1921-1928
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Journal article (peer-reviewed)abstract
- We discuss how to use coincidence detection to generate unusual, nonsinusoidal interference curves by using not a single detector, but several in coincidence. The method works for both strong (classical) and weak (on the fewphoton level) light, although in the latter case the detection becomes probabilistic with low efficiency. Using the method, one can tailor the coincidence measurement setup to obtain essentially any interference pattern. We then use the method to experimentally demonstrate phase-difference state interference patterns in the few-photon regime that are highly nonsinusoidal. We also discuss optimal implementation of the method with regard to fluctuations and success probability, and we analyze the origin and magnitude of errors.
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| 9. |
- Shirai, Tomohiro, et al.
(author)
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Imaging through an aberrating medium with classical ghost diffraction
- 2012
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In: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 29:7, s. 1288-1292
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Journal article (peer-reviewed)abstract
- We describe a method for image transmission through an aberrating medium by means of a modified configuration for conventional ghost diffraction with classical incoherent beams. On the basis of optical coherence theory, we show that the effects of phase disturbances, be they deterministic or random, can be canceled out in our method and the squared modulus of the Fourier transform of the object is obtained in terms of intensity-correlation measurements. From the measurement data, the object can be reconstructed using standard phase retrieval algorithms.
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| 10. |
- Voipio, Timo, et al.
(author)
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Partial polarization theory of pulsed optical beams
- 2013
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In: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 30:1, s. 71-81
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Journal article (peer-reviewed)abstract
- We introduce a consistent matrix formalism for the characterization of partial polarization and coherence of random, nonstationary electromagnetic beams in time and frequency domains. We derive the temporal and spectral degrees of polarization and the Stokes parameters in terms of the time-domain and frequency-domain polarization matrices. The connections between temporal polarization and spectral coherence on the one hand and spectral polarization and temporal coherence on the other hand are discussed. Additionally, we establish equivalence theorems for fields with different temporal coherence properties to have the same spectral polarization states and for fields with different spectral coherence properties to possess identical temporal polarization. The theory is illustrated by analyzing specific examples of time-domain and frequency-domain electromagnetic Gaussian Schell-model pulsed beams.
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