| 1. |
- Dinasquet, Julie, et al.
(author)
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Cascading effects of the ctenophore Mnemiopsis leidyi on the planktonic food web in a nutrient-limited estuarine system
- 2012
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In: Marine Ecology Progress Serie. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 460, s. 49-61
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Journal article (peer-reviewed)abstract
- Increasing biomasses of gelatinous zooplankton presumably have major implications for the structure and function of marine food webs at large; however, current data on lower trophic levels are scarce, as most studies have focused on the immediate effects on zooplankton and fish larvae only. We examined the short-term impact of larvae and adults of the invasive ctenophore Mnemiopsis leidyi on a summer planktonic food web in the estuarine southern Baltic Sea, with special emphasis on the microbial loop. Grazing by M. leidyi reduced the mesozooplankton biomass, followed by increased dinoflagellate biomass in treatments with M. leidyi. While chlorophyll a increased most in the treatments with M. leidyi, small phytoplankton and ciliates decreased in all treatments. M. leidyi had a slight effect on bacterial abundance, but not on bacterial production, ectoenzymatic activities, or community composition. Undetectable levels of phosphate and a gradual accumulation of dissolved organic carbon during the experiment suggested a malfunctioning microbial loop scenario. The experiment shows that direct and indirect short-term effects of M. leidyi on the estuarine food web are limited to higher trophic levels and indicates that top-down and bottom-up consequences of M. leidyi expansions on the microbial loop will likely depend on local nutrient conditions.
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| 2. |
- Hakkarainen, T., et al.
(author)
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Imaging of interacting nano-objects with superlenses
- 2012
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In: Biomedical Optics, BIOMED 2012. - Washington, D.C. : Optical Society of America. - 9781557529428
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Conference paper (peer-reviewed)abstract
- Employing rigorous electromagnetic theory we show that near-field imaging of point-like objects with subwavelength resolution is achieveable with nanoslab superlenses. For a metallic lens the resolution is »λ/5, whereas for a metamaterial lens λ/10 is obtained. We also illustrate how the near-field interactions among the objects and the lens affect the imaging.
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| 3. |
- Hassinen, T., et al.
(author)
-
Electromagnetic Hanbury Brown-Twiss phenomenon
- 2011
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In: Proc SPIE Int Soc Opt Eng. - : SPIE. - 9780819487971
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Conference paper (peer-reviewed)abstract
- We analyze the classic Hanbury Brown-Twiss effect for thermal electromagnetic fields in space-frequency domain. We compare two different approaches and show that the normalized correlation of intensity fluctuations is fully characterized by the spectral electromagnetic degree of coherence, a result analogous to scalar analysis of the effect. Differences between the two approaches are discussed.
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| 4. |
- Kellock, H., et al.
(author)
-
Higher-order ghost imaging with partially polarized classical light
- 2011
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In: Proc SPIE Int Soc Opt Eng. - : SPIE. - 9780819487971
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Conference paper (peer-reviewed)abstract
- Visibility, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) are quantities that characterize the quality of the image in ghost (or correlation) imaging. The visibility in quantum and classical ghost imaging with scalar light is known to improve as the order of imaging increases. Recently also electromagnetic ghost imaging has started to attract attention. In this work we analyze the effects of both the order of imaging and the degree of polarization (P) of the illumination on the image quality parameters. The source is a classical, partially polarized, random electromagnetic field obeying Gaussian statistics. The beam is split into several (N) parts which are directed either into the object or reference arms and the associated intensity correlations are calculated. When N > 2, more than one reference arm may exist which contributes to the background. We consider two different definitions for the visibility, as well as the SNR and CNR, and examine their attainable limiting values in second- and higher-order ghost imaging as a function of the degree of polarization. Both expressions of the visibility behave in a similar manner; they increase with the order of imaging and the degree of polarization. In second-order imaging the SNR decreases, due to increased noise, as P increases, while the CNR remains essentially constant. We emphasize that the exact numerical values depend on the definitions used and on the number of object arms in the setup.
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| 5. |
- Kellock, H., et al.
(author)
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Temporal double- and triple-intensity correlation imaging with classical light
- 2010
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In: 2010 9th Euro-American Workshop on Information Optics, WIO 2010. - 9781424482276 ; , s. 5582500-
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Conference paper (peer-reviewed)abstract
- The second- and third-order temporal ghost imaging setups with classical light are discussed. The second-order scheme has a single reference arm with a temporal lens and dispersive elements, and an object arm containing an object surrounded by dispersive media. The third-order imaging setup contains two reference arms instead of one. Both setups have a temporally completely incoherent light source providing maximum resolution. The dependence of visibility and resolution of the images on system parameters is considered in both setups.
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| 6. |
- Setälä, T., et al.
(author)
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Invisibility cloaking in weak scattering
- 2010
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In: 2010 9th Euro-American Workshop on Information Optics, WIO 2010. - 9781424482276 ; , s. 5582525-
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Conference paper (peer-reviewed)abstract
- We consider invisibility cloaking of a slab object in scalar wave theory within the first-order Born approximation.We show that in the forward direction cloaking is achieved for any object slab and incident field, whereas in the backward direction cloaking is possible at least for self-imaging fields. In both cases the scattering potential of the cloak slab depends on that of the object slab. The method of object-dependent cloaking using weak slab scatterers can be a useful addition to existing cloaking methods, for instance, in atmospheric optics and biophotonics.
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| 7. |
- Shirai, T., et al.
(author)
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Fourier synthesis in classical ghost imaging
- 2011
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In: Proceedings of Applied Industrial Optics: Spectroscopy, Imaging and Metrology, AIO 2011. - : The Optical Society. - 9781557529145
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Conference paper (peer-reviewed)abstract
- We describe an optical setup for performing spatial Fourier filtering in ghost imaging with classical incoherent light. It is shown that phase contrast imaging is possible with this setup to visualize a pure phase object.
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| 8. |
- Shirai, T., et al.
(author)
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Properties of temporal ghost imaging with classical pulses
- 2010
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In: Frontiers in Optics (FiO) 2010. - Washington, D.C. : OSA.
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Conference paper (peer-reviewed)abstract
- Temporal ghost imaging with classical pulses is described as a temporal counterpart of conventional ghost imaging with thermal light. Effects of incident pulses on the imaging condition and the resultant image quality are discussed.
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| 9. |
- Shirai, T., et al.
(author)
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Some features of temporal ghost imaging with classical light
- 2010
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In: 2010 9th Euro-American Workshop on Information Optics, WIO 2010. - 9781424482276 ; , s. 5582506-
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Conference paper (peer-reviewed)abstract
- Temporal ghost imaging with classical pulsed light is described as a temporal counterpart of conventional ghost imaging with thermal light. A temporal object to be imaged is located in the test arm while the reference arm consists of some simple temporal optical elements. The incident light is assumed to be temporally incoherent, classical pulsed light.We first show that the correlation between intensity fluctuations in these two arms is given by a fractional Fourier transform of the temporal object. In special cases, the fractional Fourier transform reduces to the ordinary Fourier transform and the image of the object. We then derive explicit expressions for the resultant ghost image under two different conditions, with a view to examining the effect of the incident pulse. As a result, it is found that the resultant temporal ghost image depends only on the single temporal variable in the reference arm though the light in this arm never interacts with the object, and that it is generally distorted by the effect of the incident pulse.
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| 10. |
- Tervo, J., et al.
(author)
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Degree of coherence and electromagnetic resonators
- 2004
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In: PHOTON MANAGEMENT. - : SPIE. - 0819453838 ; , s. 28-35
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Conference paper (peer-reviewed)abstract
- Electromagnetic theory of open laser resonators is formulated in the domain of partially coherent optics. The theory is then used to find out the electromagnetic degree of coherence of the field in various situations. It is shown that if only one transverse mode is present in the steady-state condition, then the field is necessarily completely coherent in view of the recently introduced degree of coherence for electromagnetic fields [Opt. Express. 11, 1137 (2003)].
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