| 1. |
- Petermann, Ingemar, et al.
(författare)
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Fibre Bragg characterization with ultraviolet-based interferometric side diffraction
- 2003
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Ingår i: Journal of Optics. A, Pure and applied optics. - : IOP Publishing. - 1464-4258 .- 1741-3567. ; 5:5, s. 437-441
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Tidskriftsartikel (refereegranskat)abstract
- The interferometric side diffraction method for fibre Bragg grating characterization is evaluated using a set-up with an ultraviolet interrogation beam. In its present configuration, the reproducibility errors are 2-5% for the index and typically 10degrees-20degrees for the phase profile. The reflection spectra of chirped test gratings have been successfully reproduced with the aid of the acquired phase and refractive index envelope data. It is verified that the power of the interrogating beam, within some limits, is unimportant as regards the phase reproducibility, and the importance of relating the analysis to the fabrication parameters of the grating under investigation is stressed.
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| 2. |
- Bruno, A, et al.
(författare)
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In situ detection of soot nanoparticles by time-resolved fluorescence analysis
- 2008
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Ingår i: Journal of Optics. A, Pure and Applied Optics. - : IOP Publishing. - 1741-3567 .- 1464-4258. ; 10:6, s. 5-064016
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Tidskriftsartikel (refereegranskat)abstract
- We present a new implementation of the time-resolved fluorescence anisotropy technique for the analysis of carbon nanoparticles directly in a Bunsen-type propane flame. By exploiting femtosecond laser excitation, UV-visible laser-induced fluorescence and time resolution of the experimental set-up, small soot nanoparticles have been identified within the flame. From the measurement of the decay time of the anisotropy ratio, we determined an ensemble-averaged diameter of the carbon particles of approximately 10 nm, with a slightly larger value in the outer edge of the flame compared to its centre.
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| 3. |
- Egorov, Igor
(författare)
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Second forerunners in reflection and transmission data
- 1999
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Ingår i: Journal of Optics. A, Pure and Applied Optics. - : IOP Publishing. - 1741-3567 .- 1464-4258. ; 1:1, s. 51-59
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Tidskriftsartikel (refereegranskat)abstract
- Second forerunner approximations to the transmission and reflection kernels for a temporally dispersive, nonmagnetic, isotropic slab are obtained. Numerical results are presented for two different dispersion models and are compared with the second forerunner approximations. Finally, transmission and reflection kernels are used to reconstruct the first susceptibility moments of the material of the slab.
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| 4. |
- Eriksson, Emma, 1980, et al.
(författare)
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Optical manipulation and microfluidics for studies of single cell dynamics
- 2007
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Ingår i: Journal of Optics. A, Pure and applied optics. - 1464-4258 .- 1741-3567 .- 1361-6617. ; 9:8, s. 113-121
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Tidskriftsartikel (refereegranskat)abstract
- Most research on optical manipulation aims towards investigation and development of the system itself. In this paper we show how optical manipulation, imaging and microfluidics can be combined for investigations of single cells. Microfluidic systems have been fabricated and are used, in combination with optical tweezers, to enable environmental changes for single cells. The environment within the microfluidic system has been modelled to ensure control of the process. Three biological model systems have been studied with different combinations of optical manipulation, imaging techniques and microfluidics. In Saccharomyces cerevisiae, environmentally induced size modulations and spatial localization of proteins have been studied to elucidate various signalling pathways. In a similar manner the oxygenation cycle of single red blood cells was triggered and mapped using Raman spectroscopy. In the third experiment the forces between the endoplasmic reticulum and chloroplasts were studied in Pisum sativum and Arabidopsis thaliana. By combining different techniques we make advanced biological research possible, revealing information on a cellular level that is impossible to obtain with traditional techniques.
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| 5. |
- Kröger, Ronald
(författare)
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Anti-aliasing in image recording and display hardware: lessons from nature
- 2004
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Ingår i: Journal of Optics. A, Pure and Applied Optics. - : IOP Publishing. - 1741-3567 .- 1464-4258. ; 6:8, s. 743-748
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Tidskriftsartikel (refereegranskat)abstract
- If images are undersampled during electronic recording and reproduction, regular patterns in the image may form interference patterns-aliases-with the mosaic of picture elements (pixels). Aliasing distorts visual information and is a serious technical problem. In a variety of animal eyes, images are also undersampled such that aliasing may occur. Nature's measures to reduce aliasing include (i) mosaics of photosensitive cells (pixels in technical applications) that include many spatial frequencies and are different in geometry for the basic colours red, green, and blue, (ii) electrical coupling between cells of different spectral sensitivities, and (iii) overlap between the spectral sensitivities of different cell types. Computer simulated renderings of images show that the measures are effective. Technical implementation seems to be possible in a variety of applications, such as cameras, television sets, scanners, monitors, data projectors, and digital photocopying machines.
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| 6. |
- Malkki, Pertti, et al.
(författare)
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Visualization of chromatic correction of fish lenses by multiple focal lengths
- 2005
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Ingår i: Journal of Optics. A, Pure and Applied Optics. - : IOP Publishing. - 1741-3567 .- 1464-4258. ; 7:11, s. 691-700
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Tidskriftsartikel (refereegranskat)abstract
- Many fish and some terrestrial animals have multifocal lenses that compensate for chromatic aberration by a mechanism unique to biological optical systems. We describe four optical methods for the study of such lenses. Significantly improved methods (focal-area imaging, schlieren photography, and laser scanning) are explained in full detail. One method (photorefractometry) was only slightly modified over earlier versions and is illustrated in brief. Portable equipment is available for photorefractometry, schlieren photography, and laser scanning. With our methods we could for the first time directly illustrate chromatic correction by multifocal lenses and detect a number of previously unknown optical features of fish lenses.
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| 7. |
- Blomstedt, K., et al.
(författare)
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Effective degree of coherence : general theory and application to electromagnetic fields
- 2007
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Ingår i: Journal of Optics. A, Pure and applied optics. - : IOP Publishing. - 1464-4258 .- 1741-3567. ; 9:10, s. 907-919
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Tidskriftsartikel (refereegranskat)abstract
- The concept of overall or effective degree of coherence has proven useful and insightful in the scalar theory of light. In this paper we extend the concept to fields represented over arbitrary vector (Hilbert) spaces. We show that the effective degree of coherence remains unaltered by scaled unitary mappings, which describe for instance many physical interactions. In the context of random, vector-valued electromagnetic fields the invariance implies that the effective degree of coherence assumes the same value in commonly used representation spaces. Thereby, in contrast to the local degree of coherence, this quantity can be taken as an intrinsic property of the electromagnetic wave field. In particular, the effective degree of coherence does not change when the field is scattered by a lossless medium and it can be determined from the far-field pattern. Hence the effective degree of coherence of electromagnetic fields is readily measurable.
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| 8. |
- Cai, Yangjian
(författare)
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Propagation of various flat-topped beams in a turbulent atmosphere
- 2006
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Ingår i: Journal of Optics. A, Pure and applied optics. - : IOP Publishing. - 1464-4258 .- 1741-3567. ; 8:6, s. 537-545
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of flat-topped beams with circular, elliptical and rectangular symmetries in a turbulent atmosphere is investigated. Analytical formulae for the average intensity of various flat-topped beams propagating in a turbulent atmosphere are derived in a tensor form. The formulae derived can easily be reduced to those for flat-topped beams propagating in free space (in the absence of turbulence). The propagation properties of flat-topped beams are studied in detail. We find that a flat-topped beam with circular or non-circular symmetry will evolve into a circular Gaussian beam in the far field under the influence of atmospheric turbulence, which is quite different to its properties in free space. Our method provides an effective and convenient way to analyse the propagation of various flat-topped beams in a turbulent atmosphere.
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| 9. |
- Fernando, H. N. J., et al.
(författare)
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Characterization of ultra-violet-induced changes in planar waveguides
- 2003
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Ingår i: Journal of Optics. A, Pure and applied optics. - : IOP Publishing. - 1464-4258 .- 1741-3567. ; 5:4, s. 335-340
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Tidskriftsartikel (refereegranskat)abstract
- A simple, low-cost spectrophotometer system operating in reflection absorption mode is used to characterize changes in refractive index and thickness of thin films under 193 nm irradiation. The results indicate overall dilation of the glass and are confirmed by additional surface topographic measurements. We also show that in addition to the net relaxation from laser annealing of the interface, in germanosilicate samples local compaction takes place. Since the net relaxation is triggered by remote interactions, it is not spatially confined to the laser-irradiated area. However, a local positive index change is observed. These results are in agreement with previous hypotheses put forward to explain planar waveguide negative index changes. They also bring to attention the great care necessary in both conducting and interpreting measurements that do not take into account spatial variations arising from the combination of remote and local triggers of both index and thickness changes.
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| 10. |
- Hansson, B. T., et al.
(författare)
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Pump-mode influence on the performance of end-pumped passively Q-switched lasers
- 2002
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Ingår i: Journal of Optics. A, Pure and applied optics. - : IOP Publishing. - 1464-4258 .- 1741-3567. ; 4:1, s. 29-32
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Tidskriftsartikel (refereegranskat)abstract
- We present a simple way of adjusting the output performance of end-pumped passively Q-switched lasers. The method is based on changing the size of the pump mode within the active medium, and the approach is demonstrated both in theory and in practice. We show that it is possible to modify the repetition rate from 7 kHz to 1 MHz and the pulse length from 6 to 30 ns for the laser used in the experiments.
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