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Search: L773:1996 756X OR L773:0277 786X OR L773:9781510637924 > (2000-2004)

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1.
  • Alfredson, J. (author)
  • Individual differences in visual behaviour in simulated flight
  • 2002
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4662, s. 494-502
  • Conference paper (other academic/artistic)abstract
    • Flying an aircraft is highly visually demanding. It is very important to map pilot visual behaviour, both for the purpose of evaluating the cockpit interface and to effectively integrate it with future adaptive interfaces and decision support systems. Pilots' visual behaviour was studied in two experiments. In the first experiment commercial aviation pilots were flying a commercial aviation scenario and eye point of gaze, and eye blinks were collected. In the second experiment military pilots were flying an air-to-air combat scenario and the visual behaviour was video recorded. In both of the experiments the results show individual differences in the pilots' visual behaviour. In the second experiment two different categories of eye blinks were found that might help explain the individual differences in visual behaviour. One category can be related to the systematic eye blinks found to occur when the eye point of gaze was changed between head-up/head-down and head-down/head-up. The other category could be related to other reasons, such as, mental workload or visual demands.
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2.
  • Andersen, Torben, et al. (author)
  • A parallel integrated model of the Euro50
  • 2004
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5497:1, s. 251-265
  • Conference paper (peer-reviewed)abstract
    • The Euro50 is an astronomical extremely large telescope for optical and infrared wavelength with a 50 m primary mirror. The telescope will have an elaborate control system ("live optics") to correct for atmospheric and telescope aberrations. To study and predict 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 is taken into account on the basis of wind tunnel measurements and computer fluid dynamics calculations. Atmospheric aberrations are included using a seven-layer atmosphere model. The integrated model is written in Matlab and is run on a cluster computer to achieve acceptable execution times. Dedicated ordinary differential equation solvers have been written and a special toolkit for communication between Matlab processes on different nodes of the cluster computer has been set up. Preliminary results from the complete integrated model, including adaptive optics, are shown
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3.
  • Andersen, Torben, et al. (author)
  • An integrated simulation model of the Euro50
  • 2002
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 4757, s. 84-92
  • Conference paper (peer-reviewed)abstract
    • The Euro50 is a proposed optical telescope with an equivalent aperture of 50 m. It will have a segmented primary mirror and full adaptive optics. To study the interaction of the telescope structure, the control system and the optics, an integrated simulation model has been formulated. The mechanical model is a modal version of an Ansys finite element model. The optics model is based on ray tracing and physical optics. The segments model takes the alignment servos and the segment dynamics into account. Wind variation over the primary mirror is included. Segment control system modeling is in progress. First results clearly demonstrate that a good enclosure is needed to protect the telescope well against wind. The results also suggest that the segment alignment system must have a bandwidth well above the lowest eigenfrequencies of the telescope.
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4.
  • Andersen, Torben, et al. (author)
  • Euro50
  • 2003
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5382:1, s. 169-182
  • Conference paper (peer-reviewed)abstract
    • The Euro50 is a telescope for optical and infrared wavelengths. It has an aspherical primary mirror with a size of 50 meters and 618 segments. The optical configuration is of Gregorian type and the secondary mirror is deformable for adaptive optics. Observations can take place in prime focus, Gregorian foci, and Nasmyth foci using additional relay mirrors. The telescope provides seeing limited observations, partial adaptive optics with ground layer correction, single conjugate adaptive optics and dual-conjugate adaptive optics. For prime focus observations, a clam-shell corrector with a doublet lens is used. The primary mirror segments can be polished using the precessions polishing technique. "Live Optics" denotes the joint segment alignment system, secondary mirror control system, adaptive optics and main axes servos. An overview is given of the live optics architecture, including feedback from wavefront sensors for natural and laser guide stars, and from primary mirror segment edge sensors. A straw man concept of the laser guide star system using sum-frequency YAG lasers is presented together with a solution to the laser guide star perspective elongation problem. The structural design involves a large steel structure and a tripod of carbon fiber reinforced polymer to support the secondary mirror. Integrated models have been set up to simulate telescope performance. Results show that an enclosure is needed to protect the telescope against wind during observations. The enclosure is very large box-shaped steel structure
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5.
  • Andersen, Torben, et al. (author)
  • Integrated modeling of the Euro50
  • 2003
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5382:1, s. 366-378
  • Conference paper (peer-reviewed)abstract
    • The Euro50 is a proposed 50 m optical and infrared telescope. It will have thousands of control loops to keep the optics aligned under influence of wind, gravity and thermal loads. Cross-disciplinary integrated modeling is used to study the overall performance of the Euro50. A sub-model of the mechanical structure originates from finite element modeling. The optical performance is determined using ray tracing, both non-linear and linearized. The primary mirror segment alignment control system is modeled with the 618 segments taken as rigid bodies. Adaptive optics is included using a layered model of the atmosphere and sub-models of the wavefront sensor, reconstructor and controller. The deformable mirror is, so far, described by a simple influence function and a second order dynamical transfer function but more detailed work is in progress. The model has been implemented using Matlab/Simulink on individual computers but it will shortly be implemented on a Beowulf cluster within a trusted network. Communication routines between Matlab on the cluster processors have been written and are being benchmarked. Representative results from the simulations are shown
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6.
  • Andersen, Torben, et al. (author)
  • Status of the Euro50 project
  • 2004
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5489:1, s. 407-416
  • Conference paper (peer-reviewed)abstract
    • The Euro50 is an extremely large telescope for optical and infrared wavelength with a 50 m primary mirror. It has a segmented, aspherical primary mirror and an aspherical, deformable secondary in a Gregorian layout. A tentative conceptual design exists and has been documented in a study report. Recent activities have concentrated on the science case for extremely large telescopes in the 50 m class and on identification of potential technical "show stoppers". The science case investigation has identified four fields of particular interest. The studies of critical technical issues have concentrated on atmospheric dispersion effects for high-resolution adaptive optics for extremely large telescopes, and on the influence of wind and other disturbances on wavefront control. Wind load on the telescope, the primary mirror and the enclosure has been studied using wind tunnel measurements and computational fluid dynamics. The impact of wind on the total system has been investigated using an integrated model that includes the telescope structure, the primary mirror segment alignment system, the secondary mirror alignment system, and single conjugate adaptive optics using the deformable secondary mirror. The first, tentative results show that wind disturbances may be significant and that the task of correcting for wind residuals may be at least as large for the adaptive optics system as that of correcting for atmospheric aberrations. The results suggest that use of extremely large telescopes for observations of earth-like planets around nearby stars may imply a considerable challenge
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7.
  • Andersson-Engels, Stefan, et al. (author)
  • Integrated system for interstitial photodynamic therapy
  • 2003
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5142, s. 42-49
  • Conference paper (peer-reviewed)abstract
    • A novel photodynamic therapy system based on interstitial illumination using multiple fibres is under development. The aim with this system is to enable treatment of large tumour volumes and also to utilise real-time measurements to allow on-line dosimetry. Important dosimetric parameters to measure are light fluence rate, sensitizer fluorescence intensity and local blood oxygenation. A construction which allows all functions to be readily performed with a single system is presented. We believe that interstitial PDT utilising this technique may be attractive in many clinical situations.
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8.
  • Andersson-Engels, Stefan, et al. (author)
  • Integrated system for interstitial photodynamic therapy
  • 2002
  • In: Advanced Optical Devices, Technologies, and Medical Applications. - : SPIE. - 0277-786X .- 1996-756X. ; 5123, s. 293-302
  • Conference paper (peer-reviewed)abstract
    • To develop PDT beyond treatment of thin superficial tumours, to also be an efficient treatment alternative for deeply located and/or thick tumours, a system based on interstitial illumination using multiple fibres has been developed. Conditions that could benefit from such a treatment modality are for instance malignant brain tumours and tumours in the oral cavity. In interstitial PDT one needs to use multiple fibres for light delivery in order to allow treatments of tumours larger than a few millimetres in diameter. Our system consists of a laser light source, a beam-splitting system dividing the light into three or six output fibres and a custom-made dosimetry programme. The concept is then to use these fibres not only for delivering the treatment light but also to measure parameters of interest for the treatment outcome. The fluence rate of the light emitted by each fibre is measured at the positions of the other fibre tips. From these results the light dose at all positions could be recalculated. Changes in optical properties as well as bleaching and concentration of the photosensitizer during the treatment could be monitored and compensated for in the dosimetry. Tumours have been treated both in experimental studies and in patients with thick superficial Basal Cell Carcinomas. Almost all treated skin lesions responded with complete response.
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9.
  • Andersson, I., et al. (author)
  • Increasing spatial resolution by using an image sequence
  • 2001
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4380, s. 542-551
  • Conference paper (other academic/artistic)abstract
    • In this paper we present two methods for increasing the spatial resolution of images using image sequences where all frames contain the same static scene with unknown shifts. Because of the subpixel shifts, aliased frequencies appear in a slightly different way in all images, making it possibly to reconstruct frequencies above the Nyqvist frequency, thus improving the resolution. To this end, we estimate parameters in the affine transform relating the images to each other from the sequence. To show the applicability of the algorithms, many experiments have been carried out mainly using image sequences captured by a TV-camera and not only using synthetic image sequences. The results from one TV-camera sequence are presented in this report. Measurements of PSF and MTF have been carried out and the results show that we can increase the spatial resolution by almost a factor of two. This technique can be used for target identification/recognition as well as for visualization. The second method (interpolation) is possible to implement in real time.
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10.
  • Andersson, Mikael, et al. (author)
  • Modelling and Design of Admission Control Mechanisms for Web Servers using Non-linear Control Theory
  • 2003
  • In: Performance and control of next-generation communication networks : [ITCom's Conference on Performance and Control of Next-Generation Communication Networks] ; 9 - 10 September 2003, Orlando, Florida, USA (SPIE proceedings series ; vol. 5244). - : SPIE. - 1996-756X .- 0277-786X. - 0819451274 ; 5244:1, s. 53-64
  • Conference paper (peer-reviewed)abstract
    • Web sites are exposed to high rates of incoming requests. Since web sites are sensitive to overload, admission control mechanisms are often implemented. The purpose of such a mechanism is to prevent requests from entering the web server during high loads. This paper presents how admission control mechanisms can be designed and implemented with a combination of queueing theory and control theory. Since web servers behave non-linear and stochastic, queueing theory can be used for web server modelling. However, there are no mathematical tools in queueing theory to use when designing admission control mechanisms. Instead, control theory contains the needed mathematical tools. By analysing queueing systems with control theoretic methods, good admission control mechanisms can be designed for web server systems. In this paper we model an Apache web server as a GI/G/1-system. Then, we use control theory to design a PI-controller, commonly used in automatic control, for the web server. In the paper we describe the design of the controller and also how itcan be implemented in a real system. The controller has been implemented and tested together with the Apache web server. The server was placed in a laboratory network together with a traffic generator which was used to represent client requests. Measurements in the laboratory setup show how robust the implemented controller is, and how it correspond to the results from the theoretical analysis.
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11.
  • Andrekson, Peter, 1960, et al. (author)
  • Nonlinearity-based all-optical sampling of ultrahigh-bandwidth optical signals
  • 2004
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5596, s. 319-331
  • Conference paper (peer-reviewed)abstract
    • We demonstrate an all-optical waveform sampling system with simultaneous sub-mW optical signal sensitivity (20 dB SNR) and sub-picosecond temporal resolution over more than 60 nm optical bandwidth. The optical sampling was implemented by four-wave mixing in a 10 m highly nonlinear fiber using a sampling pulse source with a sampling pulse peak power of only 16 W. The sampling performance was evaluated in terms of sensitivity, temporal resolution and optical bandwidth with respect to fiber length, sampling pulse source wavelength offset from the zero-dispersion wavelength of the highly nonlinear fiber, sampling pulse peak power and walk-off due to chromatic dispersion. We also present a summary of the available methods to achieve polarization-independent optical sampling.
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12.
  • Ardeberg, Arne, et al. (author)
  • Clusters as probes of distance, evolution, and chemistry of galaxies
  • 2003
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5382:1, s. 47-56
  • Conference paper (peer-reviewed)abstract
    • Stellar clusters are highly useful as tools for determination of distances, ages and abundances of heavy elements of galaxies, also at larger distances. Their utility for these purposes has, so far, been severely limited, mainly due to image crowding. The introduction of Extremely Large Telescopes (ELTs) with full adaptive optics (AO) and near diffraction limited performance should imply a drastic improvement concerning the usefulness of clusters and the limiting distances of high quality data. We have made a study of stellar clusters as probes of distance, evolution and chemistry of galaxies at distances from one to twenty Mpc. From data on the Stromgren uvby system, partly from direct measurements taken from the literature, we have synthesized test clusters, one open and one globular, as well as galactic backgrounds. The clusters have been embedded in the backgrounds and located at distances between one and twenty Mpc. Here, vby data have been measured, reduced and analyzed. Color-magnitude diagrams (CMDs), metallicity diagrams (MDs) and luminosity functions (LFs) have been constructed. They have been evaluated absolutely and compared to the corresponding template data. We conclude that with a 50 m AO ELT, for open as well as globular clusters, MDs are of high quality for clusters out to and beyond 5 Mpc and useful out to 10 Mpc. CMDs are of very high quality well beyond 5 Mpc. They are of high scientific value out to and beyond 10 Mpc and valuable for clusters even out to 20 Mpc. LFs are highly informative well beyond 10 Mpc and still rather valuable at 20 Mpc. With sufficient measurement data available, LFs are useful for clusters in galaxies even beyond 20 Mpc
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13.
  • Ardeberg, Arne, et al. (author)
  • Diffraction-limited light collection: Promises and challenges of a 50 m ELT
  • 2004
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5489:PART 1, s. 23-34
  • Conference paper (peer-reviewed)abstract
    • Programmes driving ELT design are discussed. The nature and evolution of circum-stellar shells and planetary discs are attractive, while the small angular sizes place basic properties, asymmetry and warps, beyond VLT capability. An ELT is neeed to reveal the conversion processes shell - disc - planets, planetary systems, Earth-like planets, habitability and life signatures. Formation and evolution of massive stars are dicussed as are stellar rotation and shape, surface spatial and temporal resolution and evolution. Stellar clusters are discussed as probes of galactic evolution, resolving CMDs for Virgo and Fornax cluster galaxies. High-resolution studies of AGNs are discussed as are supernovae with bearing on early star formation, galactic activity and cosmology. Finally, the requirements defined from the prime science drivers are confronted with technical realities.
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14.
  • Ardeberg, Arne, et al. (author)
  • Evolution of distant galaxies from cluster photometry: a program for a 50-m ELT
  • 2004
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5489:1, s. 72-83
  • Conference paper (peer-reviewed)abstract
    • The formation, shaping and evolution of galaxies are processes of high interest but poorly known. This is true also for our closest galactic neighbours. Of key importance is a representative sample of all major types of galaxies with solid evolutionary parameters. Stellar clusters are excellent probes of galactic evolution, albeit so far useful at smaller distances only, mainly due to the limiting effects of image crowding. With extremely large telescopes (ELTs) with full adaptive optics (AO) and near diffraction limited performance, the effects of image crowding will be drastically reduced. Thus, the excellence of clusters of stars as evolutionary probes can be extended out to cosmological distances. We have studied this extension. With data on the Str
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15.
  • Ardeberg, Arne, et al. (author)
  • Science drivers of a 50-m AO telescope
  • 2003
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5382:1, s. 37-46
  • Conference paper (peer-reviewed)abstract
    • Some leading science programs undertaken with Very Large Telescopes and challenges driving the progress of the Extremely Large Telescopes are discussed together with the corresponding requirements. They concern expolanets, Earth-like planets, habitable zones, formation of stars and galaxies, first stars and cosmology. A description is attempted
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16.
  • Billger, Monica, 1961, et al. (author)
  • Perception of Colour and Space in Virtual Reality: a comparison between a real room and virtual reality models
  • 2004
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5292, s. 90-98
  • Conference paper (peer-reviewed)abstract
    • Virtual Reality has great potential to become a usable design tool for the planning of light and colour in buildings. The technical development has provided us with better computer graphics and faster rendering techniques. However, the reliability and usability is delimited by lack of knowledge about how humans perceive spatial colour phenomena. The setting up of parameters for material properties in light calculation software is done arbitrarily. We present a comparison between a real room and a digital model evaluated on a desktop PC and in an Immersive Projection Technology (IPT) type system. Data were collected from video recorded interviews and questionnaires. The participants assessed the appearance of light, colours and space. They also evaluated their involvement in solving this task, and their presence in each environment. Our results highlight the benefits and disadvantages of the real and virtual models. The participants had difficulties in estimating the size of both the desktop room and the room in the ITP system. The comparison of real and virtual rooms revealed unsatisfying differences in shadowing and colour appearance. We defined the magnitude of perceived colour reflections in the real room, and elaborated with some of the parameters in Lightscape/3dsmax6.
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17.
  • Dam, J. S, et al. (author)
  • Fiber optic system for in vivo real-time determination of tissue optical properties from steady-state diffuse reflectance measurements
  • 2000
  • In: PHOTON MIGRATION, DIFFUSE SPECTROSCOPY AND OPTICAL COHERENCE TOMOGRAPHY: IMAGING AND FUNCTIONAL ASSESSMENT. - : SPIE. - 0277-786X .- 1996-756X. - 0819438162 ; 1:31, s. 103-109
  • Conference paper (peer-reviewed)abstract
    • We present a versatile and compact fiber optic probe for real-time determination of the absorption and the reduced scattering coefficients from spatially resolved continuous wave diffuse reflectance measurements. The probe collects the diffuse reflectance at six distances in the range 0.6 - 7.8 mm at four arbitrary wavelengths, which were 660, 785, 805, and 974 nm in these experiments. The maximum sampling rate for one cycle of measurements including all four wavelengths is about 100 Hz. The absorption and the reduced scattering coefficients are extracted real-time from the probe measurements using multivariate calibration methods based on multiple polynomial regression and Newton-Raphson algorithms. The system was calibrated on a 6x7 matrix of Intralipid/ink phantoms with optical properties within typical biological ranges, e.g. at 785 nm, the ranges of the absorption and the reduced scattering coefficients, were 0 - 0.3 /cm and 6 - 16 /cm, respectively. Cross-validation tests shoved that the mean prediction error, relative to the ranges of absorption and the reduced scattering coefficients were 2.8 \% and 1.3 \%, respectively.
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18.
  • Eklundh, Lars (author)
  • Estimating leaf area index in coniferous and deciduous forests in Sweden using landsat optical sensor data
  • 2003
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 4879, s. 379-390
  • Conference paper (peer-reviewed)abstract
    • This paper reports on research to estimate leaf area index (LAI) in Swedish forests with satellite sensor data. The study is part of a research programme that aims at generating input data for process-oriented forest carbon models. Field-work was carried out in two areas in Sweden about 530 km apart, in the nemoral and boreo-nemoral forest regions. Various ways of estimating LAI in the field were tested, including litter-traps, allometric equations, and light transmission measurements. The capability of Landsat TM and ETM+ for LAI-mapping was investigated with the Nilson and Kuusk forest reflectance model. Results point to channel 3 and the mid-IR channels as particularly important for LAI estimation in coniferous stands, however, modelled reflectances were strongly influenced by background reflectances (particularly at low densities) and leaf optical properties. Top-of-canopy reflectances were derived from Landsat TM and ETM+, and their relationships with field-estimated LAI analysed. Among several vegetation indices .tested, the Moisture Stress Index (TM5 / TM4) was one of the best indices for LAI in coniferous stands. In deciduous stands relationships based on the Simple Ratio were superior, however, the explanatory power in deciduous stands was lower than in coniferous stands.
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19.
  • Eklundh, Lars, et al. (author)
  • Extracting information about vegetation seasons in Africa from pathfinder AVHRR NDVI imagery using temporal filtering and least-squares fits to asymmetric Gaussian functions
  • 2003
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 4885, s. 215-225
  • Conference paper (peer-reviewed)abstract
    • Time-series of NASA/NOAA Pathfinder AVHRR Land (PAL) data have been analysed to extract parameters describing the seasonality of vegetation in Africa. Two methods have been developed to fit smooth curves to the time-series. The first method is based on an adaptive Savitzky-Golay filtering technique, and the second on non-linear least-squares fits of asymmetric Gaussian model functions. Both processing methods involve a preliminary definition of the number and timing of growing seasons using a least-squares fit of sinusoidal functions and a second order polynomial. The fit to the sinusoidal functions is used to determine the type of seasonal pattern (uni-modal or bi-modal) and to obtain starting values for the non-linear Gaussian function fits to the data. The processing incorporates qualitative information on cloudiness from the CLAVR dataset. The resulting smooth curves are used for defining parameters describing the growing seasons. The method has been applied to PAL NDVI data, and resulting imagery have been generated that show parameters such as beginnings and ends of seasons, seasonal integrated NDVI, seasonal amplitudes etc. The results indicate that the two methods complement each other and that they may be suitable in different areas depending on the behaviour of the NDVI signal.
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20.
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21.
  • Eriksson, Fredrik, et al. (author)
  • Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion assisted sputter deposition
  • 2001
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4506, s. 84-92
  • Conference paper (other academic/artistic)abstract
    • Cr/Sc multilayers have been grown on Si substrates using DC magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. They were designed for normal reflection of the first and second order with multilayer periods of 1.692 nm and 3.381 nm, and layer thickness ratios of 0.471 and 0.237, respectively. At-wavelength soft x-ray reflectivity measurements were carried out using a reflectometer with a compact soft x-ray laser-plasma source. The multilayers were irradiated during growth with Ar ions, varying both in energy (9-113 eV) and flux, in order to stimulate the ad-atom mobility and improve the interface flatness. It was found that to obtain a maximum soft x-ray reflectivity with a low flux (Cr=0.76, Sc=2.5) of Ar ions a rather high energy of 53 eV was required. Such energy also caused intermixing of the layers. By the use of a solenoid surrounding the substrate, the arriving ion-to-metal flux ratio could be increased 10 times and the ion energy could be decreased. A high flux (Cr=7.1, Sc=23.1) of low energy (9 eV) Ar ions founded the most favourable growth condition in order to limit the intermixing with a subsistent surface flatness.
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22.
  • Fazio, Valentina, et al. (author)
  • New insights in static and dynamic properties of soluble monolayers
  • 2003
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5223, s. 38-49
  • Journal article (peer-reviewed)abstract
    • Abstract In this paper we discuss selected equilibrium and dynamic properties of adsorp-tion layers of soluble surfactants. The surface state has been investigated by nonlinearoptical techniques based on second order χ(2)effects which exhibit a high surface specificityand suppress bulk contributions. The surface tension isotherm σ(c) of the homologousseries of n-alkyldimethylphosphine (n =8 − 12) can be described by Frumkin’s equation ofstate which yields the surface interaction parameter, surface coverage and the correspondingarea per molecule A. The comparison of the surface tension σ at a given area per moleculeA reveals a strong alternation within the homologous series. Odd C2n±1 layers show alower surface tension than the adjacent even members C2n of the homologous series. Thiseffect is also present at low surface coverage (A =1.4nm2) and cannot be attributed to adifferences in the chain-packing within a crystalline state. Infrared-Visible Sum-FrequencyGeneration Spectroscopy (SFGS) has been used to monitor the orientation and chain orderwithin the aliphatic tail. SFGS spectra have been recorded for different chain lengths andat different areas per molecule. The analysis of the spectra yields an order parameterG which is proportional to the number of gauche defects within the aliphatic tail. Theodd-even effect in the surface tension turned out to be accompanied by an odd-even effectin the order parameter G. The data suggest that an ordered structure has a bigger impacton the surface tension than an unordered structure. The odd-even effect is also observedin the orientation of the terminating methyl group as retrieved by polarization dependentSFGS measurements. The data shed some light in the relation between molecular andmacroscopic properties. Furthermore surface dilatational viscoelastic properties of afluorinated amphiphile have been measured by a novel version of the oscillating bubble.The oscillating bubble method generates a non-equilibrium state by a harmonic compressionand expansion of the surface layer formed at the tip of a capillary. The surface state ismonitored by Surface Second Harmonic Generation (SHG). This technique is highly surfacespecific and discriminates between monolayer and subsurface coverage. Our set-up allowsto measure the monolayer coverage under dynamic conditions and to relate this to surfacedilatational viscosity and elasticity. For a purely elastic surface layer the prediction of theLucassen van den Temple model (LvdT) are fulfilled.
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23.
  • Flicker, Ralf, et al. (author)
  • Efficient simulation of adaptive optics technologies for the Euro50 telescope
  • 2003
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5382:1, s. 599-606
  • Conference paper (peer-reviewed)abstract
    • An efficient adaptive optics (AO) simulation code was developed, which enables first-order simulations of extremely high-order systems. The Monte-Carlo-type code employs a sparse conjugate gradient algorithm for wavefront reconstruction, and a separation of spatial frequencies into two domains to economize on the number crunching. High-order multi-conjugate adaptive optics (MCAO) systems are thereby readily simulated on a single standard PC. The code is presently being applied to MCAO design studies for the Euro50 extremely large telescope (ELT), addressing a number of issues not previously subjected to realistic simulation due to the excessive computational load. We report in this paper on the latest results obtained from simulating two specific aspects of the Euro50 AO system: turbulence prediction and laser guide star (LGS) beacon synthesis. The two studies presented here are representative examples of a number of technology studies being enabled by the new fast simulation codes
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24.
  • Forssell, G., et al. (author)
  • Measurements of polarization properties of camouflaged objects and of the denial of surfaces covered with cenospheres
  • 2003
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5075, s. 246-258
  • Conference paper (other academic/artistic)abstract
    • Camouflaged objects in a background, which are not possible to observe with conventional IR measurements without polarization, can be seen in polarization measurements.. In this paper will be shown that polarization measurements increase the possibility to detect covered objects.The denial of polarization measurements of a covered object has earlier been achieved by construction of a surface covered with cenospheres. The emissivity as a function of angle of incidence has also been investigated on this newly developed surface, which can be designed to have emission properties decided in advance. The results indicate that it is possible to use the surface materiel as a means to adapt an object to a certain optical signature. It has also been shown that the surface almost completely depolarises the emitted radiation, which makes it more difficult to observe with a polarization measurement. These properties make the surface suitable as a reference surface for polarization measurements. A more systematic development of these surfaces and investigation are reported here.
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25.
  • Fridolin, Ivo, et al. (author)
  • Measurement of solutes in dialysate using UV absorption
  • 2001
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4263, s. 40-47
  • Conference paper (other academic/artistic)abstract
    • The aim of this work was to describe a new method for optical monitoring of solutes in a spent dialysate. The method utilizes UV light absorption employing a commercially available spectrophotometer. Measurements were performed both on collected dialysate samples and on-line. The concentration of several removed solutes and electrolytes in the serum and in the dialysate was determined simultaneously using standard laboratory techniques. During on-line monitoring the spectrophotometer was connected to the fluid outlet of the dialysis machine. On-line measurements during a single hemodialysis session demonstrated a possibility to monitor deviations in the dialysator performance (e.g. dialysator in bypass). The experimental results indicated a good correlation between UV absorption and several removed solutes (urea, creatinine) in the spent dialysate. The correlation coefficient for urea and creatinine concentrations in the dialysate was very high for every individual treatment. The UV absorbance correlates well to the concentrations of several solutes thought to be uremic toxins. The results indicate that the technique can be used as a continuous, on-line method for monitoring deviations in the dialysator performance and may estimate the removal of the overall toxins. In the future, the new method will be used to evaluate parameters describing delivery of the prescribed treatment dose such as KT/V and Urea Reduction Rate (URR).
  •  
26.
  • Funke, Bernd, et al. (author)
  • New non-LTE retrieval method for atmospheric parameters from MIPAS/ENVISAT emission spectra at 5.3 μm
  • 2002
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4539, s. 396-405
  • Journal article (peer-reviewed)abstract
    • Atmospheric emissions at 5.3 μm will be measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), a high-resolution limb sounder on board the European polar platform ENVISAT, scheduled to be launched in 2001. Measured spectra at 5.3 μm contain information on important atmospheric quantities such as NO volume mixing ratio, thermospheric temperature, and chemical NO production rates. However, the scientific analysis of this spectral region has to deal with complex non-local thermodynamic equilibrium (non-LTE) effects. A conventional non-LTE retrieval approach using ab initio vibrational temperatures cannot be applied due to rotational and spin-orbit non-LTE of NO in the thermosphere, and the dependence of NO state populations on the NO abundance itself caused by chemical excitations. An innovative non-LTE retrieval method enabling the treatment of vibrational, rotational, and spin non-LTE as well as a dependence of the non-LTE state distribution on the retrieval target quantities has thus been developed for the MIPAS data analysis. The ability of the developed non-LTE inversion tool to retrieve NO abundance profiles, thermospheric temperature profiles, and NO mean production rates by NO2 photolysis in the stratosphere and N+O2 combination in the thermosphere is demonstrated by means of a feasibility study.
  •  
27.
  • Garbe, C.S., et al. (author)
  • Estimation of complex motion from thermographic image sequences
  • 2003
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5073, s. 303-317
  • Conference paper (other academic/artistic)abstract
    • In this contribution a novel technique for computing complex motion involving heat transport processes will be presented. The proposed technique is a local gradient based approach, combining transport models with motion analysis. It allows for the simultaneous estimation of both motion and parameter of an underlying transport model. Since the analysis is based on thermal image sequences, estimates are computed to a high temporal and spatial resolution, limited only by the resolution and frame rate of the employed IR camera. This novel technique was utilized on exchange processes at the atmosphere/ocean boundary, where significant parameters of heat transfer could be measured and a transport model verified. Using the presented algorithms, surface flows as well as convergences and divergences on air-water interfaces can be measured accurately. Apart from applications in oceanography and botany, relevant benefits of the proposed technique to NDT will be presented. It is possible to compensate for motion to reach accuracies much better than 1/10th of a pixel. Through the direct estimation of locally resolved diffusivities in materials, insights can be gained about defects present. By estimating not only isotropic diffusion but also the whole matrix of anisotropic diffusion, the technique is highly relevant to measurements of composite materials.
  •  
28.
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29.
  • Jensen, LK, et al. (author)
  • Optical coherence tomography in clinical examination of non-pigmented skin malignancies
  • 2003
  • In: OPTICAL COHERENCE TOMOGRAPHY AND COHERENCE TECHNIQUES. - : SPIE. - 0277-786X .- 1996-756X. - 0819450103 ; 5140, s. 160-160
  • Conference paper (peer-reviewed)abstract
    • Optical coherence tomography (OCT) images of basal cell carcinomas (BCCs) have been acquired using a compact handheld probe with an integrated video camera allowing the OCT images to be correlated to a skin surface image. In general the healthy tissue of the skin has an obvious stratified structure, whereas the cancerous tissue shows a more homogenous structure. Thus it was demonstrated that it is possible to distinguish BCCs from healthy tissue by means of OCT. Furthermore different histological types of BCC were identified. Comparison of OCT images taken prior to and immediately after photodynamic therapy clearly shows the tissue response to the treatment, and indicates local oedema in the treated area.
  •  
30.
  • Jensen, PS, et al. (author)
  • Fourier transform infrared spectroscopy of aqueous solutions using optical subtraction
  • 2002
  • In: OPTICAL DIAGNOSTICS AND SENSING OF BIOLOGICAL FLUIDS AND GLUCOSE AND CHOLESTEROL MONITORING II. - : SPIE. - 1996-756X .- 0277-786X. - 0819443638 ; 4624, s. 150-159
  • Conference paper (peer-reviewed)abstract
    • For the analysis of small concentrations of organics in aqueous solutions, a novel add-on accessory for dual-beam / optical subtraction spectroscopy has been built for a commercial Fourier transform infrared spectrometer. A standard FT-IR instrument requires a sample measurement and a separate reference measurement, whereas the optical subtraction instrument directly measures the difference between sample and reference. This has a number of advantages. The time delay between the two measurements is eliminated, and the effective measurement time is improved by a factor of two. Moreover, the optical subtraction provides a large reduction in dynamic range of the measured signal, which prevents detector saturation, and enables effective use of dynamic range of the analog to digital converter in the FT-IR spectrometer. This results in an increased signal to noise ratio, compared to the standard FT-IR instrument. By changing detector and light source the instrument may be used for both near- and mid.-infrared spectroscopy. The increased sensitivity and stability of the optical subtraction instrument compared to the standard instrument is demonstrated by transmission measurements of aqueous urea solutions in the combination band region 4000 to 5000cm(-1) (2000 to 2500nm).
  •  
31.
  • Johansson, Anders (author)
  • A neural network for photoplethysmographic respiratory rate monitoring
  • 2001
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4434, s. 109-118
  • Conference paper (other academic/artistic)abstract
    • The photoplethysmographic signal (PPG) includes respiratory components seen as frequency modulation of the heart rate (respiratory sinus arrhythmia, RSA), amplitude modulation of the cardiac pulse, and respiratory induced intensity variations (RIIV) in the PPG baseline. The aim of this study was to evaluate the accuracy of these components in determining respiratory rate, and to combine the components in a neural network for improved accuracy. The primary goal is to design a PPG ventilation monitoring system. PPG signals were recorded from 15 healthy subjects. From these signals, the systolic waveform, diastolic waveform, respiratory sinus arrhythmia, pulse amplitude and RIIV were extracted. By using simple algorithms, the rates of false positive and false negative detection of breaths were calculated for each of the five components in a separate analysis. Furthermore, a simple neural network (NN) was tried out in a combined pattern recognition approach. In the separate analysis, the error rates (sum of false positives and false negatives) ranged from 9.7% (pulse amplitude) to 14.5% (systolic waveform). The corresponding value of the NN analysis was 9.5-9.6%.
  •  
32.
  • Johansson, Ann, et al. (author)
  • Compact fiber-optic fluorosensor using high-power continuous-wave violet diode laser
  • 2003
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5141, s. 47-57
  • Conference paper (peer-reviewed)abstract
    • In this work a compact fluorosensor has been built for point-monitoring and imaging applications. The instrument has been applied in fluorescence studies on green vegetation and on malignant tissue. The instrument is based on a violet diode laser, an integrated spectrometer and optical fibers for light delivery and collection of the fluorescence signal. This combination makes the system very compact. The high laser output power allows for coupling of the laser light into a hyperspectral diagnostic imaging instrument, developed and built by Science and Technology International. In point-monitoring mode, the instrument has been tested on superficial skin tumors and when using δ-aminolevulinic acid induced protoporphyrin IX as a tumor sensitizer, good contrast between normal and malignant tissue was achieved, clearly demonstrating its feasibility in cancer diagnostics. In imaging mode, the instrument functioned solely as a light source, coupling the excitation light into the hyperspectral imaging instrument. The set-up was tested by studying chlorophyll fluorescence from vegetation. The fluorescence signal showed a low signal-to-noise ratio mainly because of inefficient light coupling into the imaging instrument.
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33.
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34.
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35.
  • Klasen, L., et al. (author)
  • Evaluation of a method for invariant and automated detection and tracking of objects from video
  • 2001
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4232, s. 455-463
  • Conference paper (other academic/artistic)abstract
    • Video generates a rich set of image information and often the useful information is only a very limited set of the available information. Another well-known fact is that visually reviewing of long video recordings is a time demanding task. In combination with the continuously increasing number of video surveillance systems, this leads to an increasing need for automated analysis of long image sequences. The goal for this work is to develop and evaluate a method for automatic detection and tracking of events recorded onto a surveillance video, such as appearance of persons or vehicles in a surveyed area, to evaluate the usefulness for forensic applications and real time applications. One core problem is the fact that both the background and the objects move, where only the physical motion of moving objects are of interest and needs to be separated from the camera motion. Another core problem in many of the video processing algorithms is parameter estimation despite invariance for accurate modeling of the desired features. Varying scale, color, lightning conditions and occlusion of the object of interest can for example cause invariance. The technical approaches for this work is to separate global and local motion by analyzing the optical flow constraints. To overcome the problem caused by such feature and object invariance, all pixels are considered independently and no feature parameters are needed. If the basic optical flow constraint is satisfied, the motion is classified as global motion. If not, the motion is considered caused by local motion, noise or other phenomena. An object that undergoes local motion can then be detected and tracked as is forms a trace in the temporal domain, while the noise appears on an intermittent basis and will be disregarded. The results from applying this method on several image sequences were compared and the robustness and ability to deal with invariance has been evaluated. The result clearly shows that in realistic situations, where visual reviewing can be quite a difficult task, computer based methods for automatic detection are useful to detected moving objects in long video recordings.
  •  
36.
  • Landré, Jérôme, et al. (author)
  • Content-based multiresolution indexing and retrieval of Paleontology images
  • 2001
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 0277-786X .- 1996-756X. ; 4315, s. 482-489
  • Journal article (peer-reviewed)abstract
    • In this article a research work in the field of content-based image retrieval in large database applied to the Paleontolgy image database of the université de Bourgogne, Dijon, France called "TRANS'TYFIPAL" is proposed. Our indexing method is based on multiresolution decomposition of database images using wavelets. For each kind of paleontology images we try to find a characteristic image representing it. This model image is computed using a classification algorithm on the space of parameters extracted from the wavelet transform of each image. Then a search tree is built to offer users a graphic interface for retrieving images. So that users have to navigate through this tree to find an image similar that of to their request. Our contribution in the field is the building of the model and of the search tree to make user access easier and faster. This paper ends with a conclusion on first coming results and a description of future work to be done to enhance our indexing and retrieval method.
  •  
37.
  • Leahy, M.J., et al. (author)
  • Developments in laser Doppler blood perfusion monitoring
  • 2002
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4876:1, s. 128-139
  • Conference paper (other academic/artistic)abstract
    • This paper reviews the development and use of laser Doppler perfusion monitors and imagers. Despite their great success and almost universal applicability in microcirculation research, they have had great difficulty in converting to widespread clinical application. The enormous interest in microvascular blood perfusion coupled with the 'ease of use' of the technique has led to 2000+ publications citing its use. However, useful results can only be achieved with an understanding of the basic principles of the instrumentation and its application in the various clinical disciplines. The basic technical background is explored and definitions of blood perfusion and laser Doppler perfusion are established. The calibration method is then described together with potential routes to standardisation. A guide to the limitations in application of the technique gives the user a clear indication of what can be achieved in new studies as well as possible inadequacy in some published investigations. Finally some clinical applications have found acceptability and these will be explored.
  •  
38.
  • Linderhed, A., et al. (author)
  • Analysis of optical measurements on real minefields
  • 2002
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4742:I, s. 160-171
  • Conference paper (other academic/artistic)abstract
    • This paper presents preliminary analysis of the data from measurements on a minefield in Croatia done in the international cooperation project Airborne Minefield Area Reduction (ARC). Temperature differences above and around suspected mines and minefield indicators, were recorded with a long wave IR camera in 8-9 µm, over a time of several days, capturing data under different weather conditions. The data are compared to simulations of land mines, minefield indicators and other objects using a themodynamic FEM model, developed at FOI. Different detection methods are presented and applied to the data.
  •  
39.
  • López-Puertas, M., et al. (author)
  • Non-LTE studies for the analysis of MIPAS/ENVISAT data
  • 2002
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4539, s. 381-395
  • Journal article (peer-reviewed)abstract
    • The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a high-resolution limb sounder on board the European polar platform ENVISAT, scheduled for launch late in 2001. Three main characteristics converge in MIPAS which make it a very useful instrument for non-LTE studies: its wide spectral coverage (4.15-14.6 μm or 680-2275 cm-1); high spectral resolution (0.03 cm-1), and high sensitivity; all of this in addition to its global spatial coverage. In this paper we present an overview of the non-LTE studies that have been carried out in preparation for the analysis of MIPAS data, including the evaluation of non-LTE effects in the operational processing, focussed in the stratosphere, and the retrieval of species that normally emit under non-LTE conditions. The current mission plan for measuring the non-LTE upper atmosphere is described, as well as the general purpose non-LTE retrieval scheme developed for analyzing those measurements.
  •  
40.
  • Lu, W., et al. (author)
  • Application of combinatorial material chip method on the improvement of quantum dots emission efficiency
  • 2004
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5277:1, s. 99-108
  • Conference paper (peer-reviewed)abstract
    • The combinatorial material chip method has been used to study the emission efficiency of InAs/GaAs quantum dots. The photoluminescence spectroscopy is performed to obtain the rule of emission efficiency on the proton implantation dose. A pronounced enhancement of room temperature emission efficiency has been obtained by the optimized quantum dots process condition. The increment of emission efficiency up to 80 itmes has been observed. This effect may be resulted from both the proton passivation and carrier capture enhancement effects. The maximum photoluminescence peak shift is about 23 meV resulted from the intermixing of quantum dots. A linear dependence behavior has been observed for both the non-radiative recombination time and carrier relaxation time on the ion-implantation dose. The maximum enhancement of the photoluminescence is observed in the proton implantation dose of 1.0 x 1014 cm-2 followed by rapid thermal annealing at 700°C. These effects will be useful for the QDs' optoelectronic devices.
  •  
41.
  • Marcks von Würtemberg, Rickard, et al. (author)
  • Fabrication and performance of 1.3-μm vertical cavity surface emitting lasers with InGaAs quantum well active regions grown on GaAs substrates
  • 2004
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5443, s. 229-239
  • Journal article (peer-reviewed)abstract
    • We describe the development of long-wavelength InGaAs/GaAs vertical-cavity surface emitting lasers (VCSELs). Using highly strained double-quantum wells (DQWs) in combination with negative gain-cavity detuning we have been able to realise such VCSELs with emission wavelength up to 1300 nm. High-performance device characteristics include mW-range output power, mA-range threshold currents, 10 Gbit/s data transmission and very good temperature stability with continuous-wave operation up to at least 140degreesC. Singlemode emission is realised using an integrated mode filter consisting of a patterned silicon layer on the out-coupling mirror surface, yielding output power and threshold currents for 1270-nm devices of 1.2 - 0.5 mW and 2.3 - 0.6 mA, respectively, over a temperature interval of 10 - 140degreesC. Multimode devices have been found to deliver more than 2 mW at 1290 nm. Preliminary lifetime measurements do not reveal any intrinsic reliability problems related to the highly strained quantum wells.
  •  
42.
  • Miroshnikova, N., et al. (author)
  • Study of the interaction mechanisms between different materials and pulses from CO2- and Nd:YAG-lasers using digital speckle photography
  • 2004
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5506, s. 42-50
  • Journal article (peer-reviewed)abstract
    • Pulsed irradiation from CO2- and Nd:YAG lasers focused on the front side of different plates produces nearly instantaneous surface changes on the rear side of the plate. The responses of the materials depend on physical parameters such as pulse energy and duration, photon energy, the absorption and mechanical characteristics of the target material. The equipment built up for visualization of these phenomena consists of a cw. He-Ne laser, a digital CCD camera and a fast computer. The analysis is done using Digital Speckle Photography (DSP). Using focused and defocused laser speckle patterns, DSP enables measurement of in-plane strain fields, Brownian motion and residual micro-structural changes in the material caused by a laser pulse. Results are obtained at the frame rate of the digital camera and allow the creation of animated real-time or "movie" sequences. Results from CO2- and Nd:YAG pulse interaction on Al2O3 ceramics and steel plates will be presented. The Brownian motion during the relaxation phase is more or less localized to the impacted area for both materials and both wavelengths but the relaxation times differ significantly. Steel also exhibits some residual material changes and doesn't recover completely while Al2O3 returns to its initial state some time after the impact
  •  
43.
  • Monemar, Bo, et al. (author)
  • Optical properties of InGaN/GaN and AlGaN/GaN multiple quantum well structures
  • 2003
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5023, s. 63-67
  • Conference paper (other academic/artistic)abstract
    • We report on low temperature photoluminescence (PL) in In xGa1-xN multiple quantum wells (MQWs) with x in the range 0.1 and highly Si doped barriers of In0.01Ga0.99N. One sample with 3 QWs of width 3.5 nm and barriers of width 10.5 nm had the MQW in the depletion region of the outer surface. Two PL peaks were observed, one QW exciton from the QW closest to the GaN buffer, one lower energy peak related to a 2DEG at the interface to the GaN buffer layer. In a second similar sample 5 QWs of width 3 nm and with 6 nm highly Si doped In0.01Ga 0.99N barriers the MQW was placed in the n-side depletion region of a pn-junction. At low temperatures the PL and electroluminescence (EL) spectra are quite different at no, low, or reverse bias, the PL appearing at higher energy. At high forward bias a spectral component at the EL position appears. This proves a strong influence of the depletion field on the optical spectra. Preliminary results are also reported for n-doped Al0.07Ga 0.93N/GaN structures, with near surface MQWs.
  •  
44.
  • Moraru, Dan, et al. (author)
  • Integrated modeling of submillimeter radio telescopes
  • 2002
  • In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 4757, s. 169-173
  • Conference paper (peer-reviewed)abstract
    • Integrated models are inherently complex and often obscure to any but those who write them. Their usefulness can be greatly enhanced through well-structured, object-oriented design. A robust and computationally efficient Simulink/C++ library of optics, control, finite-element, and visualization routines for modeling radio telescope performance under various operating conditions is being developed and is described. The library is being developed in conjunction with an end-to-end model of the Atacama Large Millimeter Array (ALMA) antennas. The model includes the mechanical structure, optics, servos, and potential laser gyros, and can be used to investigate such issues as tracking performance, compliance with error budgets, wind sensitivity, and effectiveness of an internal metrology system. It will also be a good tool for comparison of different antenna designs.
  •  
45.
  • Mukherjee, S.D., et al. (author)
  • Critical parameters for parallel interconnects using VCSEL arrays and fiber image guides
  • 2002
  • In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4942, s. 292-305
  • Conference paper (other academic/artistic)abstract
    • Several thousand glass optical fibers fused together is routinely used as fiber image guides for medical and other image remoting applications. Fiber image guides also offer possibility for flexible optical interconnect links with potentially thousands of bi-directional parallel channels with data rates as high as 10 Gbps per channel, leading to more than Tera bits per second aggregate data transfer rates. A fair number of fiber image guide based link demonstrations using vertical cavity surface emitting lasers have been reported. However, little is known about designable parameters and optimization paradigms for applications to massively parallel optical interconnects. This paper discusses critical optical parameters that characterize a massively parallel link. Experimental characterizations were carried out to explore some of the fundamental interactions between single-mode 850 nm VCSELs and fiber image guides having different numerical apertures, 0.25, 0.55 and 1.00. Preliminary optical simulation results are given. Finally, potential directions for further experimental and analytical explorations, and for applicability into designable link systems are suggested.
  •  
46.
  • Owner-Petersen, Mette, et al. (author)
  • Some consequences of atmospheric dispersion for ELTs
  • 2004
  • In: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5489:1, s. 507-517
  • Conference paper (peer-reviewed)abstract
    • Previously the effect of atmospheric dispersion on telescope performance has attracted only relatively little attention. This may be due to the fact that the dispersion effects have been evaluated in relation to the size of the diffraction limited resolution angle of current telescopes, or to seeing limited telescopes. However, since the resolution angle is inversely proportional to telescope diameter, dispersion and dispersion compensation becomes increasingly important for extremely large telescopes (ELTs). In this paper we present a simple model for the dispersion effects in telescopes with adaptive optics (AO). The model addresses the expected loss in Strehl ratio when the atmospheric wavefront error is measured at a wavelength different from the wavelength of observation. Also, the bandwidth over which the correction will be of a given quality is evaluated. Related to AO performance, the consequence of using laser guide stars (LGSs) for probing the atmosphere may be that the measured wavefront error must be rescaled to the wavelength of observation. This places special demands on the AO control loop. Since linear atmospheric dispersion compensation need not cover a larger bandwidth than the AO compensation, an atmospheric dispersion compensator (ADC) can be designed for narrow band operation. As an example of the benefits to be obtained from this, we briefly present the proposed ADC for the Euro50
  •  
47.
  • Paeglis, R, et al. (author)
  • Eye model with controllable lens scattering
  • 2001
  • In: HYBRID AND NOVEL IMAGING AND NEW OPTICAL INSTRUMENTATION FOR BIOMEDICAL APPLICATIONS. - : SPIE. - 0277-786X .- 1996-756X. - 0819441481 ; 4434, s. 233-238
  • Conference paper (peer-reviewed)abstract
    • A model of human eye for experiments in vision research has been developed using PLZT ceramics. This ``artificial eye{''} allows to simulate light scattering caused by cataract in the eye lens. Light scattering of a composite eye lens of the model depends on the electric field applied to a transparent electrooptic PLZT ceramics plate that is attached directly to the lens. The image degradation in such a model eye at various degrees of scattering is studied observing and recording the contrast of images on the ``retinal plane{''} created by standard test objects with different spatial frequency or by a He-Ne laser source passing a diffractive transparent placed before the eye.
  •  
48.
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49.
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50.
  • Pifferi, A, et al. (author)
  • Multi-distance optical characterization of the female breast by time-resolved diffuse spectroscopy
  • 2003
  • In: PHOTON MIGRATION AND DIFFUSE-LIGHT IMAGING. - : SPIE. - 1996-756X .- 0277-786X. - 0819450081 ; 5138, s. 6-11
  • Conference paper (peer-reviewed)abstract
    • Two systems for time-resolved diffuse spectroscopy were used for the optical characterization of the female breast in 4 volunteers. A first system was a compact laser diode instrument operated at 660 and 785 nm, while the second one was a broadband laboratory set-up based on mode-locked lasers tunable in the 610-1000 nm range. Measurements were obtained both in transmittance and in reflectance geometry at 5 inter-fiber distances ranging from I to 4 cm at different locations on the breast. Distinct spectral features both in absorption and in scattering were observed among the 4 volunteers, and for each subject between reflectance and transmittance measurements. These differences are correlated with the abundance of the glandular tissue and blood absorption. Upon increasing, the inter-fiber distance in reflectance, deeper tissue structures were investigated, generally resulting in higher water contribution.
  •  
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