| 11. |
- Björström, Cecilia M., et al.
(författare)
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Influence of solvents and substrates on the morphology and the performance of low-bandgap polyfluorene:PCBM photovoltaic devices
- 2006
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - Cardiff : SPIE - International Society for Optical Engineering. - 0277-786X .- 1996-756X. ; 6192, s. 61921X-
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Tidskriftsartikel (refereegranskat)abstract
- Spin-coated thin films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (APFO-3) blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are used as the active material in polymer photovoltaic cells. Such blends are known for their tendency to phase separate during film formation. Tuning the morphology of the blend in a controlled way is one possible road towards higher efficiency. We studied the effect of adding chlorobenzene to chloroform-based blend solutions before spin-coating on the conversion efficiency of APFO-3:PCBM photodiodes, and related that to the lateral and vertical morphology of thin films of the blend. The lateral morphology is imaged by atomic force microscopy (AFM) and the vertical compositional profile is obtained by dynamic secondary ion mass spectrometry (SIMS). The profiles reveal compositional variations consisting of multilayers of alternating polymer-rich and PCBM-rich domains in the blend film spin-coated from chloroform. The vertical compositional variations are caused by surface-directed spinodal waves and are frozen in during the rapid evaporation of a highly volatile solvent. With addition of the low-vapour pressure solvent chlorobenzene, a more homogeneous vertical composition is found. The conversion efficiency for solar cells of this blend was found to be optimal for chloroform:chlorobenzene mixtures with a volume-ratio of 80:1. We have also investigated the role of the substrate on the morphology. We found that blend films spin-coated from chloroform solutions on PEDOT:PSS-coated ITO show a similar compositional structure as the films on silicon, and that changing the substrate from silicon to gold only affects the vertical phase separation in a region close to the substrate interface
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| 12. |
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| 13. |
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| 14. |
- Chen, Daru, et al.
(författare)
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Some switchable dual-wavelength fibre lasers based on fibre Bragg grating feedback
- 2006
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6351, s. U864-U872
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Tidskriftsartikel (refereegranskat)abstract
- Two methods to achieve dual-wavelength switching in a fibre laser are proposed and two corresponding switchable dual-wavelength fibre lasers based on fibre Bragg grating (FBG) feedback are demonstrated in this paper. In one proposed fibre laser, both Raman and Erbium-doped fibre (EDF) pumps are employed and the dual-wavelength switching is achieved by controlling the power of the Raman pump. In the other proposed fibre laser, an injection technique is used and the dual-wavelength switching is realized by controlling the power of the injection laser. The detailed behavior of the dual-wavelength switching in the two fibre lasers is experimentally studied and the principle is explained physically.
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| 15. |
- Chen, Jiajia, et al.
(författare)
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A Novel Joint Scheduling Algorithm for Multiple Services in 10G EPON
- 2008
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 7137
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, we propose and evaluate a novel joint scheduling algorithm for multiple services which can support differentiated services and bandwidth allocation with global priority of different traffic such as Triple-play: voice, video and Internet services. Simulation results show that for the higher priority traffic better delay and jitter performance can be achieved compared with the lower priority traffic.
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| 16. |
- Dravins, Dainis, et al.
(författare)
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Toward a diffraction-limited square-kilometer optical telescope: Digital revival of intensity interferometry - art. no. 698609
- 2008
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Ingår i: Extremely Large Telescopes: Which Wavelengths? Retirement Symposium for Arne Ardeberg. - : SPIE. - 0277-786X .- 1996-756X. ; 6986, s. 98609-98609
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Konferensbidrag (refereegranskat)abstract
- Much of the progress in astronomy follows imaging with improved resolution. In observing stars, current capabilities are only marginal in beginning to image the disks of a few, although many stars will appear as surface objects for baselines of hundreds of meters. Since atmospheric turbulence makes ground-based phase interferometry challenging for such long baselines, kilometric space telescope clusters have been proposed for imaging stellar surface details. The realization of such projects remains uncertain, but comparable imaging could be realized by ground-based intensity interferometry. While insensitive to atmospheric turbulence and imperfections in telescope optics, the method requires large flux collectors, such as being set up as arrays of atmospheric Cherenkov telescopes for studying energetic gamma rays. High-speed detectors and digital signal handling enable very many baselines to be synthesized between pairs of telescopes, while stars may be tracked across the sky by electronic time delays. First observations with digitally combined optical instruments have now been made with pairs of 12-meter telescopes of the VERITAS array in Arizona. Observing at short wavelengths adds no problems, and similar techniques on an extremely large telescope could achieve diffraction-limited imaging down to the atmospheric cutoff, achieving a spatial resolution significantly superior by that feasible by adaptive optics operating in the red or near-infrared.
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| 17. |
- Eastham, D. A., et al.
(författare)
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Construction of a new type of low-energy, scanning electron microscope with atomic resolution
- 2009
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - Monterey : SPIE. - 0277-786X .- 1996-756X. - 9780819476548 ; 7378, s. 73781S-73781S
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Konferensbidrag (refereegranskat)abstract
- We describe a new type of scanning electron microscope which works by directly imaging the electron field-emission sites on a nanotip. Electrons are extracted from the nanotip through a nanoscale aperture, accelerated in a high electric field and focussed to a spot using a microscale einzel lens. If the whole microscope (accelerating section and lens) and the focal length are both restricted in size to below 10 microns, then computer simulations show that the effects of aberration are extremely small and it is possible to have a system with approximately unit magnification, at electron energies as low as 300 eV. Thus a typical emission site of 1 nm diameter will produce an image of the same size and an atomic emission site with give a resolution of 0.1-0.2 nm (1-2 Å), and because the beam is not allowed to expand beyond 100nm in diameter the depth of field is large and the contribution to the beam spot size from chromatic aberrations is less than 0.02 nm (0.2 Å) for 500 eV electrons. Since it is now entirely possible to make stable atomic sized emitters (nanopyramids) it is expected that this instrument will have atomic resolution. Furthermore the brightness of the beam is determined only by the field-emission and can be up to a million times larger than in a typical (high-energy) electron microscope. The construction of this microscope, based on using a nanotip electron source which is mounted on a nanopositioner so that it can be positioned at the correct point adjacent to the microscope, entrance aperture, is described. In this geometry the scanning is achieved by moving the sample using piezos. Two methods for the construction of the microscope column are reviewed and the results of preliminary tests are described. The advantages of this low energy, bright-beam, electron microscope with atomic resolution are described. It can be used in either scanning mode or diffraction mode. The major advantage over existing microscopes is that because it works at very low energies the elastic backscatteri g is sensitive to the atomic species and so these can be identified directly without any energy discrimination on the detector. Furthermore it is also possible to use the microscope to do low energy electron diffraction which, because the scattering cross-section is large, can be carried out on single molecules. If these are biological samples such as DNA, proteins and viruses then the low energy means that the radiation damage is minimised. Some possibilities for mounting these samples, which can reduce radiation damage, are discussed. Finally we show a system for producing holograms of single protein molecules.
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| 18. |
- Engström, David, 1976, et al.
(författare)
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Steering accuracy of a spatial light modulator-based single beam steerer: guidelines and limitations
- 2008
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Ingår i: SPIE Proceedings. - : SPIE. - 0277-786X .- 1996-756X. - 9780819472588
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Konferensbidrag (refereegranskat)abstract
- The positioning accuracy when a phase-only one dimensional spatial light modulator (SLM) is used for beam steering is limited by the number of pixels and their quantized phase modulation. Optimizing the setting of the SLM pixels individually can lead to the inaccuracy being a significant fraction of the diffraction limited spot size. This anomalous behaviour was simulated numerically, and experiments showed the same phenomena with very good agreement. However, by including an extra degree of freedom in the optimization of the SLM setting, we show that the accuracy can be improved by a factor proportional to the number of pixels in the SLM.
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| 19. |
- Enmark, Anita, et al.
(författare)
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Architecture of the integrated model of the Euro50
- 2006
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Ingår i: Modeling, Systems Engineering, and Project Management for Astronomy II. - : SPIE. - 0277-786X .- 1996-756X. ; 6271, s. 27114-27114
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Konferensbidrag (refereegranskat)abstract
- The Euro50 is a proposed 50m extremely large telescope for optical and infrared wavelengths. To study and predict the performance of the complete telescope system, an integrated model combining the structural model of the telescope, optics models, the control systems and the adaptive optics has been established. Wind and atmospheric disturbances are also included in the model. The model is written in MATLAB and C. It is general and modular and built around dedicated ordinary differential equation solvers. The difference in time constants between subsystems is exploited to speed up calculations. The solvers can handle discontinuities and subsystem mode changes. The high degree of modularity allows different telescope designs to be modelled by rearranging subsystem blocks. Certain subsystems, for instance adaptive optics, can also run in a standalone fashion. Parts of the model are parallelized for execution on a large shared memory machine. The resulting architecture of the integrated model and sample results using the code for different telescope models are presented.
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| 20. |
- Enmark, Anita, et al.
(författare)
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Modeling ELTs at different wavelengths
- 2008
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Ingår i: Extremely Large Telescopes: Which Wavelengths? Retirement Symposium for Arne Ardeberg. - : SPIE. - 0277-786X .- 1996-756X. ; 6986, s. 9860-9860
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Konferensbidrag (refereegranskat)abstract
- The next generation of telescopes, the Extremely Large Telescopes (ELTs), will have a multitude Of control loops to maintain nearly diffraction-limited performance in the presence of atmospheric turbulence and external disturbances, for instance from wind. Integrated simulation models combining structural and optical modeling together with control system modeling are efficient tools for prediction of performance of ELTs. Such models include submodels of structures, adaptive optics, atmosphere, wind load, deformable mirrors and a segmented primary mirror. So far the models applied have been applicable to observations in the K-band. However, there is a desire to also operate the ELTs with adaptive optics at wavelengths in the visible range. We here give estimates of the feasibility of performing such simulations. We set up scaling laws for the design parameters as a function of wavelength of operation and we show that the execution time for an integrated model of an ELT depends dramatically on the operation wavelength. We also discuss the consequences of different choices of model refinement. Finally we present estimates of the execution time for integrated models of ELTs. We show that accurate modeling in the K-band calls for long execution times, even with parallel computers. For wavelengths in the visible range, only the very simplest models are feasible due to execution time limitations, thereby precluding many interesting studies related to noise sensitivity and limiting magnitude for guide stars.
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