| 1. |
- Sondhauss, Peter, et al.
(author)
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Picosecond x-ray studies of coherent folded acoustic phonons in a periodic semiconductor heterostructure
- 2006
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 6118, s. 1180-1180
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Conference paper (peer-reviewed)abstract
- Zone folded coherent acoustic phonons were generated in a multilayered GaSb/InAs epitaxial heterostructure via rapid heating by femtosecond laser pulses. These phonons were probed by means of ultrafast x-ray diffraction. Phonons both from the fundamental acoustic branch and the first back-folded branch were detected. This represents the first clear evidence for phonon branch folding based directly on the atomic motion to which x-ray diffraction is sensitive. From a comparison of the measured phonon-modulated x-ray reflectivity with simulations, evidence was found for a reduction of the laser penetration depth. This reduction can be explained by the self-modulation of the absorption index due to photogenerated free carriers.
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| 2. |
- Batista, P.D., et al.
(author)
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Acousto-electric single-photon detector
- 2007
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6583, s. 658304-
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Journal article (peer-reviewed)abstract
- We propose a novel concept for a semiconductor-based single-photon detector for quantum information processing, which is capable of discriminating the number of photons in a light pulse. The detector exploits the charge transport by a surface acoustic wave (SAW) in order to combine a large photon absorption area (thus providing high photon collection efficiency) with a microscopic charge detection area, where the photo generated charge is detected with resolution at the single electron level using single electron transistors (SETs). We present preliminary results on acoustic transport measured in a prototype for the detector as well as on the fabrication of radio-frequency single-electron transistors (RFSETs) for charge detection. The photon detector is a particular example of acousto-electric nanocircuits that are expected to be able to control both the spatial and the spin degrees of freedom of single electrons. If realized, these circuits will contribute substantially to a scalable quantum information technology.
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| 3. |
- Güsten, R., et al.
(author)
-
APEX - The Atacama Pathfinder Experiment
- 2006
-
In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6267 I
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Conference paper (peer-reviewed)abstract
- APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world's outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.
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| 4. |
- Björström, Cecilia M., et al.
(author)
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Influence of solvents and substrates on the morphology and the performance of low-bandgap polyfluorene:PCBM photovoltaic devices
- 2006
-
In: 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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Journal article (peer-reviewed)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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| 5. |
- Eastham, D. A., et al.
(author)
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Construction of a new type of low-energy, scanning electron microscope with atomic resolution
- 2009
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In: Proceedings of SPIE - The International Society for Optical Engineering. - Monterey : SPIE. - 0277-786X .- 1996-756X. - 9780819476548 ; 7378, s. 73781S-73781S
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Conference paper (peer-reviewed)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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| 6. |
- Kuzmin, Leonid, 1946
(author)
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A Parallel/Series Array of Cold-Electron Bolometers with SIN Tunnel Junctions for Cosmology Experiments
- 2008
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819472304 ; 7020:3, s. 1-9
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Conference paper (peer-reviewed)abstract
- A novel concept of the parallel/series array of Cold-Electron Bolometers (CEB) with Superconductor-Insulator-Normal (SIN) Tunnel Junctions has been proposed for matching with JFET readout. The current-biased CEBs are connected in series for DC and in parallel for HF signal. A signal is concentrated to the absorber through the capacitance of tunnel junctions and additional capacitance for coupling of superconducting islands. Due to dividing power between CEBs in the array and increasing responsivity, the noise matching could be effectively optimized and the photon Noise Equivalent Power could be easily achieved at 300 mK with a room temperature JFET readout.
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| 7. |
- Abrahamsson, Christoffer, et al.
(author)
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Scatter correction of transmission NIR spectra by photon migration data - Quantitative analysis of solids
- 2005
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 6009, s. 60090-60090
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Conference paper (peer-reviewed)abstract
- The scope of this presentation is a new methodology to correct conventional NIR data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation, measured by conventional NIR spectroscopy. The main advantage of this is that the absorption coefficient is independent of the path length of the light inside the sample, and therefore independent of the scattering effects. The measurements in this work were made using a novel system for time-resolved measurements, based on short light continuum pulses generated in an index-guided crystal fibre and a spectrometer-equipped streak camera. The system enables spectral recordings in the wavelength range 500 - 1200 nm with a spectral resolution of 5 nm and a temporal resolution of 30 ps. The evaluation scheme is based on modeling of light transport by diffusion theory, that provides an independent measure of the scattering properties of the samples, that later is used to correct conventional NIR data. This yields a clear advantage over other pre-processing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. PLS calibration models shows that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to models based on conventional NIR data. The method also makes it possible to predict the concentration of active substance in samples with physical properties different from those of the samples included in the calibration model.
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| 8. |
- Andersen, Torben, et al.
(author)
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A new concept for large deformable mirrors for extremely large telescopes
- 2006
-
In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 6272:1, s. 324-331
-
Conference paper (peer-reviewed)abstract
- For extremely large telescopes, there is strong need for thin deformable mirrors in the 3-4 m class. So far, feasibility of such mirrors has not been demonstrated. Extrapolation from existing techniques suggests that the mirrors could be highly expensive. We give a progress report on a study of an approach for construction of large deformable mirrors with a moderate cost. We have developed low-cost actuators and deflection sensors that can absorb mounting tolerances in the millimeter range, and we have tested prototypes in the laboratory. Studies of control laws for mirrors with thousands of sensors and actuators are in good progress and simulations have been carried out. Manufacturing of thin, glass mirror blanks is being studied and first prototypes have been produced by a slumping technique. Development of polishing procedures for thin mirrors is in progress
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| 9. |
- Andersen, Torben, et al.
(author)
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An Integrated Model of the European Extremely Large Telescope
- 2008
-
In: MODELLING, SYSTEMS ENGINEERING, AND PROJECT MANAGEMENT FOR ASTRONOMY III. - : SPIE. - 1996-756X .- 0277-786X. ; 7017, s. 216-227
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Conference paper (peer-reviewed)abstract
- Integrated models including optics, structures, control systems, and disturbances are important design tools for Extremely Large Telescopes (ELTs). An integrated model has keen formulated for the European ELT and it includes telescope structure, main servos, primary mirror segment control system, wind, optics, wavefront sensor, deformable mirror, and an AO reconstructor and controller. There are three model phases: Initialization, execution of a solver to determine time responses, and post-processing. In near future, the model will be applied for performance studies and design trade-offs for the European ELT.
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| 10. |
- Ardeberg, Arne, et al.
(author)
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ELTs, adaptive optics and wavelengths - art. no. 698608
- 2008
-
In: Extremely Large Telescopes: Which Wavelengths? Retirement Symposium for Arne Ardeberg. - : SPIE. - 1996-756X .- 0277-786X. ; 6986, s. 98608-98608
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Conference paper (peer-reviewed)abstract
- A number of Extremely Large Telescopes for visual-infrared and adjacent wavelengths are in various degrees of progress. All have primary mirrors with equivalent diameters larger than 20 m and are intended for operation with adaptive optics systems. We discuss several ELT observing parameters as functions of wavelength. Stellar energy distributions and atomic line spectra are inspected as are the transmission of the Earth's atmosphere, the emissivity of the sky and telescope and instruments as well as detector sensitivity, resolution and signal-to-noise ratio. The spatial resolution depending on the size of the diffraction limited adaptive optics point spread function is discussed. We have evaluated the ELT efficiency in terms of Johnson V to N band photometry, simulating diffraction-limited ELT images of a stellar field at 4 Mpc and 4 kpc, respectively. We conclude that the information content at shorter wavelengths is of dominant nature and that there is every reason to do the utmost to include shorter wavelengths in the AO regime. We propose to adopt a short-wave length goal of 1 000 nm for first light AO with later updates reaching down to visual wavelengths.
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