| 1. |
- Hakkarainen, T., et al.
(author)
-
Near-field imaging of interacting nano objects with metal and metamaterial superlenses
- 2012
-
In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 14, s. 043019-
-
Journal article (peer-reviewed)abstract
- Employing rigorous electromagnetic theory we investigate optical the near-field imaging of two interacting dipole-like objects with metal and slightly lossy metamaterial nanoslab superlenses. Our analysis indicates that the dipole emission is suppressed by near-field interactions when the objects are close to the lens or each other. This strongly influences the image quality, in particular with objects of small size and high polarizability. The interference from two nearby objects also affects the resolution and subwavelength definition can only be obtained for objects with dipole moments predominantly orthogonal to the slab. Such an optimal imaging condition is achieved with excitation by total internal reflection. With simulations we show that in these circumstances, subwavelength resolutions of about lambda/5 for silver superlens and lambda/10 for metamaterial slab are reached.
|
|
| 2. |
- Hakkarainen, T., et al.
(author)
-
Near-field imaging of point dipole with silver superlens
- 2010
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 101:4, s. 731-734
-
Journal article (peer-reviewed)abstract
- Making use of exact and quasistatic expressions for the field in near-field imaging of a point dipole by a thin silver slab, we calculate the point-spread function and the associated image resolution. We show that the resolution, which depends on the silver slab thickness and the dipole orientation, generally is better than the conventional diffraction limit and can be as high as lambda/8. The results substantially agree with recent theoretical and experimental studies on 2D objects.
|
|
| 3. |
- Hassinen, T., et al.
(author)
-
Hanbury Brown-Twiss effect with electromagnetic waves
- 2011
-
In: Optics Express. - 1094-4087. ; 19:16, s. 15188-15195
-
Journal article (peer-reviewed)abstract
- The classic Hanbury Brown-Twiss experiment is analyzed in the space-frequency domain by taking into account the vectorial nature of the radiation. We show that as in scalar theory, the degree of electromagnetic coherence fully characterizes the fluctuations of the photoelectron currents when a random vector field with Gaussian statistics is incident onto the detectors. Interpretation of this result in terms of the modulations of optical intensity and polarization state in two-beam interference is discussed. We demonstrate that the degree of cross-polarization may generally diverge. We also evaluate the effects of the state of polarization on the correlations of intensity fluctuations in various circumstances.
|
|
| 4. |
- Shirai, T., et al.
(author)
-
Classical ghost diffraction enabling aberration-corrected imaging
- 2012
-
In: Frontiers in Optics, FIO 2012. - 9781557529565
-
Conference paper (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 and show theoretically that the method enables aberration-corrected imaging.
|
|
| 5. |
- Alonso, M. A., et al.
(author)
-
Optimal pulses for arbitrary dispersive media
- 2011
-
In: Journal of the European Optical Society-Rapid Publications. - : European Optical Society. - 1990-2573. ; 6, s. 11035-
-
Journal article (peer-reviewed)abstract
- A variational procedure is given for finding the pulses for which the initial temporal rms width and the rate of increase of this width are jointly minimized for propagation in non-absorbing media with arbitrary dispersive properties. We show that, while in linearly dispersive media the optimal pulses are Gaussian, in other situations such as a hollow metallic waveguide or for purely cubic dispersion departures from Gaussian behavior become evident. An interpretation of the results in terms of suitable phase-space representations is also given.
|
|
| 6. |
- Bezemer, T. M., et al.
(author)
-
Divergent composition but similar function of soil food webs of individual plants: plant species and community effects
- 2010
-
In: Ecology. - 0012-9658. ; 91:10, s. 3027-3036
-
Journal article (peer-reviewed)abstract
- Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.
|
|
| 7. |
- Lindberg, J., et al.
(author)
-
Coherence and polarization properties of a three-dimensional, primary, quasi-homogeneous, and isotropic source and its far field
- 2010
-
In: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 283:22, s. 4452-4456
-
Journal article (peer-reviewed)abstract
- We study the spatial coherence properties of a three-dimensional, primary, quasi-homogeneous, and isotropic source and the far field that it generates. We assess the spectrum, degree of polarization, electromagnetic degree of coherence, and effective degree of coherence of the source and of the far field. We also demonstrate the formalism for a spherical Gaussian Schell-model current source. The polarization properties of light are fully accounted for in the analysis, and it is found that certain results pertaining to scalar coherence theory are reproduced also within the electromagnetic treatment.
|
|
| 8. |
- de Vries, Franciska T., et al.
(author)
-
Soil food web properties explain ecosystem services across European land use systems
- 2013
-
In: Proceedings of the National Academy of Sciences. - Washington, DC : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 110:35, s. 14296-14301
-
Journal article (peer-reviewed)abstract
- Intensive land use reduces the diversity and abundance of many soil biota, with consequences for the processes that they govern and the ecosystem services that these processes underpin. Relationships between soil biota and ecosystem processes have mostly been found in laboratory experiments and rarely are found in the field. Here, we quantified, across four countries of contrasting climatic and soil conditions in Europe, how differences in soil food web composition resulting from land use systems (intensive wheat rotation, extensive rotation, and permanent grassland) influence the functioning of soils and the ecosystem services that they deliver. Intensive wheat rotation consistently reduced the biomass of all components of the soil food web across all countries. Soil food web properties strongly and consistently predicted processes of C and N cycling across land use systems and geographic locations, and they were a better predictor of these processes than land use. Processes of carbon loss increased with soil food web properties that correlated with soil C content, such as earthworm biomass and fungal/bacterial energy channel ratio, and were greatest in permanent grassland. In contrast, processes of N cycling were explained by soil food web properties independent of land use, such as arbuscular mycorrhizal fungi and bacterial channel biomass. Our quantification of the contribution of soil organisms to processes of C and N cycling across land use systems and geographic locations shows that soil biota need to be included in C and N cycling models and highlights the need to map and conserve soil biodiversity across the world.
|
|
| 9. |
- Hakkarainen, Timo, et al.
(author)
-
Electromagnetic near-field interactions of a dipolar emitter with metal and metamaterial nanoslabs
- 2011
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 84:3, s. 033849-
-
Journal article (peer-reviewed)abstract
- We investigate the emission properties of a polarizable point dipole placed within a subwavelength distance from a silver or a slightly absorbing, negative-index metamaterial nanoslab. Using electromagnetic theory we show that in the immediate vicinity of the slab the dipole-slab interaction prevents the dipole from radiating. For the metamaterial slab close to the perfect-lens arrangement, the interaction is relatively weak and of short range. In particular, a region exists in the near zone of the metamaterial slab where the dipole emission is not disturbed by the interaction, and a bright intensity distribution of subwavelength width is created on the opposite side of the slab. This suggests that a low-loss metamaterial slab can act as a near-field imaging device which does not disturb the object. For the silver slab the interaction is stronger and it reaches over the near-field zone, adversely influencing the imaging capabilities in terms of brightness and resolution. The results are important for the development of metal and metamaterial superlenses.
|
|
| 10. |
- Norrman, Andreas, et al.
(author)
-
Partial spatial coherence and partial polarization in random evanescent fields on lossless interfaces
- 2011
-
In: Journal of the Optical Society of America A-OPTICS IMAGE SCIENCE AND VISION. - Washington D.C. : OPTICAL SOC AMER. - 1084-7529. ; 28:3, s. 391-400
-
Journal article (peer-reviewed)abstract
- We consider partial spatial coherence and partial polarization of purely evanescent optical fields generated in total internal reflection at an interface of two dielectric (lossless) media. Making use of the electromagnetic degree of coherence, we show that, in such fields, the coherence length can be notably shorter than the light's vacuum wavelength, especially at a high-index-contrast interface. Physical explanation for this behavior, analogous to the generation of incoherent light in a multimode laser, is provided. We also analyze the degree of polarization by using a recent three-dimensional formulation and show that the field may be partially polarized at a subwavelength distance from the surface even though it is fully polarized farther away. The degree of polarization can assume values unattainable by beamlike fields, indicating that electromagnetic evanescent waves generally are genuine three-dimensional fields. The results can find applications in near-field optics and nanophotonics.
|
|
