| 1. |
- Parlato, L., et al.
(författare)
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Investigation of dark counts in innovative materials for superconducting nanowire single-photon detector applications
- 2017
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510609594 ; 10229, s. Article no 102290I-
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Konferensbidrag (refereegranskat)abstract
- The phenomenon of dark counts in nanostripes of different superconductor systems such as high-temperature superconducting YBa 2 Cu 3 O 7-x and superconductor/ferromagnet hybrids consisting of either NbN/NiCu or YBa 2 Cu 3 O 7-x /L 0.7 Sr 0.3 MnO 3 bilayers have been investigated. For NbN/NiCu the rate of dark-count transients have been reduced with respect to pure NbN nanostripes and the events were dominated by a single vortex entry from the edge of the stripe. In the case of nanostripes based on YBa 2 Cu 3 O 7-x , we have found that thermal activation of vortices was also, apparently, responsible for triggering dark-count signals.
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| 2. |
- Abrahamsson, Christoffer, et al.
(författare)
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Scatter correction of transmission NIR spectra by photon migration data - Quantitative analysis of solids
- 2005
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 6009, s. 60090-60090
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Konferensbidrag (refereegranskat)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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| 3. |
- Achilles, Silvio, et al.
(författare)
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GPU-Accelerated Coupled Ptychographic Tomography
- 2022
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Ingår i: Developments in X-Ray Tomography XIV. - : SPIE. - 0277-786X .- 1996-756X. - 9781510654686 ; 12242
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Konferensbidrag (refereegranskat)abstract
- Scanning coherent X-ray microscopy (ptychography) has gained considerable interest during the last decade since the performance of this indirect imaging technique does not necessarily rely on the quality of the X-ray optics and, in principle, can achieve highest spatial resolution in X-ray imaging. The method can be easily extended to 3D by adding standard tomographic reconstruction schemes. However, the tomographic reconstruction is often applied in a subsequent step using a sequence of aligned ptychographic 2D projections. In this contribution, we outline current developments of a GPU-accelerated framework for direct 3D ptychography, coupling 2D ptychography and tomography. The program utilizes a custom GPU-accelerated framework for ptychography that offers three distinct ptychographic reconstruction algorithms. The tomographic reconstruction runs simultaneously and uses numerical routines of the ASTRA Toolbox. This parallel-computing approach results in a high performance increase considerably reducing the reconstruction time of 3D ptychographic datasets.
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| 4. |
- Adler, Alexandre, et al.
(författare)
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Modelling ground pickup for microwave telescopes
- 2022
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 12190
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Tidskriftsartikel (refereegranskat)abstract
- Microwave telescopes require an ever-increasing control of experimental systematics in their quest to measure the Cosmic Microwave Background (CMB) to exquisite levels of precision. One important systematic for ground and balloon-borne experiments is ground pickup, where beam sidelobes detect the thermal emission of the much warmer ground while the main beam is scanning the sky. This generates scan-synchronous noise in experiment timestreams, which is difficult to filter out without also deleting some of the signal from the sky. Therefore, efficient modelling of pickup can help guide the design of experiments and of analysis pipelines. In this work, we present an extension to the BEAMCONV algorithm that enables us to generate time-ordered data (TOD) from beam-convolved sky and ground maps simultaneously. We simulate ground pickup for both a ground-based experiment and a telescope attached to a stratospheric balloon. Ground templates for the balloon experiment are obtained by re-projecting satellite maps of the Earth's microwave emission.
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| 5. |
- Afanasiev, Sergey V., et al.
(författare)
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Experimental apparatus to study crystal channeling in an external SPS beamline
- 2007
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6634
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Tidskriftsartikel (refereegranskat)abstract
- For the new generation of high intensity hadronic machines as, for instance, LHC, halo collimation is a necessary issue for the accelerator to operate at the highest possible luminosity and to prevent the damage of superconductor magnets.1 We propose an experiment aimed to systematic study of the channeling phenomenology and of the newly observed "volume reflection" effect. This experiment will be performed for an external SPS beamline and will make use of a primary proton beam with 400 GeV/c momentum and very small (∼ 3 μrad) divergence. The advantage of a proposed experiment is precise tracking of particles that interacted with a crystal, so that to determine the single-pass efficiency for all the processes involved. For this purpose, a telescope equipped with high-resolution silicon microstrip detectors will be used. New generation silicon crystals and an extra-precise goniometer are mandatory issues. Main goal of the experiment is to get the precise information on channeling of relativistic particles and, ultimately, on the feasibility of such technique for halo collimation at LHC. In this contribution we review the status of the setting-up of experimental apparatus and its future development in sight of the planned run in September 2006.
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| 6. |
- Alexander, Naomi E., et al.
(författare)
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IMAGINE project : A low cost, high performance, monolithic passive mm-wave imager front-end
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819492852
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Konferensbidrag (refereegranskat)abstract
- The FP7 Research for SME project IMAGINE - a low cost, high performance monolithic passive mm-wave imager front-end is described in this paper. The main innovation areas for the project are: i) the development of a 94 GHz radiometer chipset and matching circuits suitable for monolithic integration. The chipset consists of a W-band low noise amplifier, fabricated using the commercially available OMMIC D007IH GaAs mHEMT process, and a zero bias resonant interband tunneling diode, fabricated using a patented epi-layer structure that is lattice matched to the same D007IH process; ii) the development of a 94 GHz antenna adapted for low cost manufacturing methods with performance suitable for real-time imaging; iii) the development of a low cost liquid crystal polymer PCB build-up technology with performance suitable for the integration and assembly of a 94 GHz radiometer module; iv) the assembly of technology demonstrator modules. The results achieved in these areas are presented.
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| 7. |
- Alfredson, J.
(författare)
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Individual differences in visual behaviour in simulated flight
- 2002
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4662, s. 494-502
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 8. |
- Andersen, Torben, et al.
(författare)
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A new concept for large deformable mirrors for extremely large telescopes
- 2006
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Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 6272:1, s. 324-331
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Konferensbidrag (refereegranskat)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.
(författare)
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A parallel integrated model of the Euro50
- 2004
-
Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5497:1, s. 251-265
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Konferensbidrag (refereegranskat)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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| 10. |
- Andersen, Torben, et al.
(författare)
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An Integrated Model of the European Extremely Large Telescope
- 2008
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Ingår i: MODELLING, SYSTEMS ENGINEERING, AND PROJECT MANAGEMENT FOR ASTRONOMY III. - : SPIE. - 1996-756X .- 0277-786X. ; 7017, s. 216-227
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Konferensbidrag (refereegranskat)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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| 11. |
- Andersen, Torben, et al.
(författare)
-
An integrated simulation model of the Euro50
- 2002
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 4757, s. 84-92
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Konferensbidrag (refereegranskat)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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| 12. |
- Andersen, Torben, et al.
(författare)
-
Euro50
- 2003
-
Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5382:1, s. 169-182
-
Konferensbidrag (refereegranskat)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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| 13. |
- Andersen, Torben, et al.
(författare)
-
Integrated modeling of the Euro50
- 2003
-
Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5382:1, s. 366-378
-
Konferensbidrag (refereegranskat)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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| 14. |
- Andersen, Torben, et al.
(författare)
-
Status of the Euro50 project
- 2004
-
Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5489:1, s. 407-416
-
Konferensbidrag (refereegranskat)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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| 15. |
- Andersson-Engels, Stefan, et al.
(författare)
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Integrated system for interstitial photodynamic therapy
- 2003
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5142, s. 42-49
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Konferensbidrag (refereegranskat)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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| 16. |
- Andersson-Engels, Stefan, et al.
(författare)
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Integrated system for interstitial photodynamic therapy
- 2002
-
Ingår i: Advanced Optical Devices, Technologies, and Medical Applications. - : SPIE. - 0277-786X .- 1996-756X. ; 5123, s. 293-302
-
Konferensbidrag (refereegranskat)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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| 17. |
- Andersson, I., et al.
(författare)
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Increasing spatial resolution by using an image sequence
- 2001
-
Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4380, s. 542-551
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 18. |
- Andersson, Mikael, et al.
(författare)
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Modelling and Design of Admission Control Mechanisms for Web Servers using Non-linear Control Theory
- 2003
-
Ingår i: 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
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Konferensbidrag (refereegranskat)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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| 19. |
- Andreani, P., et al.
(författare)
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The European ALMA Regional Centre: a model of user support
- 2014
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819496171 ; 9149, s. Art. no. 91490Y-
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Konferensbidrag (refereegranskat)abstract
- The ALMA Regional Centres (ARCs) form the interface between the ALMA observatory and the user community from the proposal preparation stage to the delivery of data and their subsequent analysis. The ARCs provide critical services to both the ALMA operations in Chile and to the user community. These services were split by the ALMA project into core and additional services. The core services are financed by the ALMA operations budget and are critical to the successful operation of ALMA. They are contractual obligations and must be delivered to the ALMA project. The additional services are not funded by the ALMA project and are not contractual obligations, but are critical to achieve ALMA full scientific potential. A distributed network of ARC nodes (with ESO being the central ARC) has been set up throughout Europe at the following seven locations: Bologna, Bonn-Cologne, Grenoble, Leiden, Manchester, Ondrejov, Onsala. These ARC nodes are working together with the central node at ESO and provide both core and additional services to the ALMA user community. This paper presents the European ARC, and how it operates in Europe to support the ALMA community. This model, although complex in nature, is turning into a very successful one, providing a service to the scientific community that has been so far highly appreciated. The ARC could become a reference support model in an age where very large collaborations are required to build large facilities, and support is needed for geographically and culturally diverse communities.
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| 20. |
- Andrekson, Peter, 1960, et al.
(författare)
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Nonlinearity-based all-optical sampling of ultrahigh-bandwidth optical signals
- 2004
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5596, s. 319-331
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Konferensbidrag (refereegranskat)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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| 21. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Bi-metal coated aperture SNOM probes
- 2011
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819486608 ; 8070
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Konferensbidrag (refereegranskat)abstract
- Aperture probes of scanning near-field optical microscopes (SNOM) offer resolution which is limited by a sum of the aperture diameter at the tip of a tapered waveguide probe and twice the skin depth in metal used for coating. An increase of resolution requires a decrease of the aperture diameter. However, due to low energy throughput of such probes aperture diameters usually are larger than 50 nm. A groove structure at fiber core-metal coating interface for photon-to-plasmon conversion enhances the energy throughput 5-fold for Al coated probes and 30-fold for Au coated probes due to lower losses in the metal. However, gold coated probes have lower resolution, first due to light coupling from the core to plasmons at the outside of the metal coating, and second due to the skin depth being larger than for Al. Here we report on the impact of a metal bilayer of constant thickness for coating aperture SNOM probes. The purpose of the bilayer of two metals of which the outer one is aluminum and the inner is a noble metal is to assure low losses, hence larger transmission. Using body-of-revolution finite-difference time-domain simulations we analyze properties of probes without corrugations to measure the impact of using a metal bilayer and choose an optimum bi-metal configuration. Additionally we investigate how this type of metalization works in the case of grooved probes.
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| 22. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Magnetic probe for material characterization at optical frequencies
- 2011
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819486608 ; 8070
-
Konferensbidrag (refereegranskat)abstract
- Rapid development of novel, functional metamaterials made of purely dielectric, plasmonic, or composite structures which exhibit tunable optical frequency magnetic responses creates a need for new measurement techniques. We propose a method of actively measuring magnetic responses, i.e. magnetic dispersion, of such metamaterials within a wide range of optical frequencies with a single probe by exciting individual elementary cells within a larger matrix. The probe is made of a tapered optical fiber with a radially corrugated metal coating. It concentrates azimuthally polarized light in the near-field below the apex into a subwavelength size focus of the longitudinal magnetic field component. An incident azimuthally polarized beam propagates in the core until it reaches the metal stripes of constant angular width running parallel to the axis. For a broad frequency range light-to-plasmon coupling is assured as the lattice constant changes with the radius due to constant angular width. Bound plasmonic modes in slits between the metal stripes propagate toward the apex where circular currents in stripes and displacement currents in slits generate a strong longitudinal magnetic field. The energy density of the longitudinal magnetic component in the vicinity of the axis is much stronger than that of all the other components combined, what allows for pure magnetic excitation of magnetic resonances rather than by the electric field. The scattered signal is then measured in the far-field and analyzed.
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| 23. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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On the optical properties of plasmonic glasses
- 2014
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628415568 ; 9441, s. Art. no. 94411G-
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Konferensbidrag (refereegranskat)abstract
- We report on the optical properties of plasmonic glasses which are metal-dielectric composites composed of metallic inclusions in a host dielectric medium. The investigated structures are of quasi-random nature, described by the pair correlation function, featuring a minimum center-to-center distance between metallic inclusions and long range randomness. Plasmonic glasses exhibiting short-range order only may be fabricated using bottom-up, self-assembly methods and have been utilized in a number of applications such as plasmonic sensing or plasmon-enhanced solar harvesting, and may be also employed for certain non-linear applications. It is therefore important to quantify their properties. Using theoretical methods we investigate optical of 1D, 2D, and 3D structures composed of amorphous distributions of metallic spheres. It is shown, that the response of the constituent element, i.e. The single sphere localized surface plasmon resonance, is modified by the scattered fields of the other spheres in such a way that its peak position, peak amplitude, and full-width at half-maximum exhibit damped oscillations. The oscillation amplitude is set by the particle density and for the peak position may vary by up to 0.3 eV in the optical regime. Using a modified coupled dipole approach we calculate the effective (average) polarizability of plasmonic glasses and discuss their spectra as a function of the dimensionality, angle of incidence and polarization, and the minimum center-to-center distance. The analytical model is complemented and validated by T-Matrix calculations of the optical cross-sections of amorphous arrays of metallic spheres obtained using a modification of the Random Sequential Adsorption algorithm for lines, surfaces, and volumes.
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| 24. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Optical activity of catalytic elements of hetero-metallic nanostructures
- 2015
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628416237 ; 9502
-
Konferensbidrag (refereegranskat)abstract
- Interaction of light with metals in the form of surface plasmons is used in a wide range of applications in which the scattering decay channel is important. The absorption channel is usually thought of as unwanted and detrimental to the efficiency of the device. This is true in many applications, however, recent studies have shown that maximization of the decay channel of surface plasmons has potentially significant uses. One of these is the creation of electron-hole pairs or hot electrons which can be used for e.g. catalysis. Here, we study the optical properties of hetero-metallic nanostructures that enhance light interaction with the catalytic elements of the nanostructures. A hybridized LSPR that matches the spectral characteristic of the light source is excited. This LSPR through coupling between the plasmonic elements maximizes light absorption in the catalytic part of the nanostructure. Numerically calculated visible light absorption in the catalytic nanoparticles is enhanced 12-fold for large catalytic disks and by more 30 for small nanoparticles on the order of 5 nm. In experiments we measure a sizable increase in the absorption cross section when small palladium nanoparticles are coupled to a large silver resonator. These observations suggest that heterometallic nanostructures can enhance catalytic reaction rates.
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| 25. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Sensing (un)binding events via surface plasmons: Effects of resonator geometry
- 2016
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510601291 ; 9884
-
Konferensbidrag (refereegranskat)abstract
- The resonance conditions of localized surface plasmon resonances (LSPRs) can be perturbed in any number ways making plasmon nanoresonators viable tools in detection of e.g. phase changes, pH, gasses, and single molecules. Precise measurement via LSPR of molecular concentrations hinge on the ability to confidently count the number of molecules attached to a metal resonator and ideally to track binding and unbinding events in real-time. These two requirements make it necessary to rigorously quantify relations between the number of bound molecules and response of plasmonic sensors. This endeavor is hindered on the one hand by a spatially varying response of a given plasmonic nanosensor. On the other hand movement of molecules is determined by stochastic effects (Brownian motion) as well as deterministic flow, if present, in microfluidic channels. The combination of molecular dynamics and the electromagnetic response of the LSPR yield an uncertainty which is little understood and whose effect is often disregarded in quantitative sensing experiments. Using a combination of electromagnetic finite-difference time-domain (FDTD) calculations of the plasmon resonance peak shift of various metal nanosensors (disk, cone, rod, dimer) and stochastic diffusion-reaction simulations of biomolecular interactions on a sensor surface we clarify the interplay between position dependent binding probability and inhomogeneous sensitivity distribution. We show, how the statistical characteristics of the total signal upon molecular binding are determined. The proposed methodology is, in general, applicable to any sensor and any transduction mechanism, although the specifics of implementation will vary depending on circumstances. In this work we focus on elucidating how the interplay between electromagnetic and stochastic effects impacts the feasibility of employing particular shapes of plasmonic sensors for real-time monitoring of individual binding reactions or sensing low concentrations - which characteristics make a given sensor optimal for a given task. We also address the issue of how particular illumination conditions affect the level of uncertainty of the measured signal upon molecular binding.
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| 26. |
- Ardeberg, Arne, et al.
(författare)
-
Clusters as probes of distance, evolution, and chemistry of galaxies
- 2003
-
Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5382:1, s. 47-56
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Konferensbidrag (refereegranskat)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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| 27. |
- Ardeberg, Arne, et al.
(författare)
-
Diffraction-limited light collection: Promises and challenges of a 50 m ELT
- 2004
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5489:PART 1, s. 23-34
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Konferensbidrag (refereegranskat)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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| 28. |
- Ardeberg, Arne, et al.
(författare)
-
ELTs, adaptive optics and wavelengths - art. no. 698608
- 2008
-
Ingår i: Extremely Large Telescopes: Which Wavelengths? Retirement Symposium for Arne Ardeberg. - : SPIE. - 1996-756X .- 0277-786X. ; 6986, s. 98608-98608
-
Konferensbidrag (refereegranskat)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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| 29. |
- Ardeberg, Ame, et al.
(författare)
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ELTs, AO wavelengths and science output
- 2008
-
Ingår i: GROUND-BASED AND AIRBORNE TELESCOPES II, PTS 1-3. - 0277-786X .- 1996-756X. ; 7012, s. 121-121
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Konferensbidrag (refereegranskat)abstract
- A study is presented of the impact on science data from extremely large telescopes of a transformation of wavelength base for optimization of actuator architecture from 2 200 to 1250 nm. From the optical path difference (OPD) data for Euro50, we transform to E-ELT OPDs. We compute the corresponding power spectrum, in which we simulate a higher actuator density via high-pass filtering to convert from K to J band actuator-pitch optimization. From the modified power spectrum we derive the correspondingly modified OPDs, PSFs and Strehl ratios. A massive improvement is demonstrated resulting from converting from AO@K to AO@J. This result is followed up by model-based E-ELT imaging in a field in a galactic disc at a distance of 4 Mpc. The improvements in image quality, background and limiting magnitude are very large as are the increases in photometric precision derived from the field imaging. Further, the great science benefit and large opportunities provided by partial AO is demonstrated. In conclusion, while admittedly challenging, pushing AO optimization to wavelengths as short as possible is of prime concern for the science output of ELTs.
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| 30. |
- Ardeberg, Arne, et al.
(författare)
-
Evolution of distant galaxies from cluster photometry: a program for a 50-m ELT
- 2004
-
Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5489:1, s. 72-83
-
Konferensbidrag (refereegranskat)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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| 31. |
- Ardeberg, Arne, et al.
(författare)
-
From Euro50 towards a European ELT
- 2006
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6267 II, s. 26725-26725
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Konferensbidrag (refereegranskat)abstract
- With Euro50 as a convenient telescope laboratory, the Euro50 team has continued development aiming at a European extremely large telescope (ELT). Here, we give a progress report. The needs of science and instrumentation are briefly discussed as is the importance of photometric stability and precision. Results are reported from work on integrated modelling. Details are given concerning point-spread functions (PSFs) obtained with and without adaptive optics (AO). Our results are rather encouraging concerning AO photometry and compensation of edge sensor noise as well as regarding seeing-limited ELT operation. The current status of our development of large deformable mirrors is shown. Low-cost actuators and deflection sensors have been developed as have hierarchic control algorithms. Fabrication of large thin mirror blanks as well as polishing and handling of thin mirrors has been studied experimentally. Regarding adaptive optics, we discuss differential refraction and the limitations imposed by dispersive optical path differences (OPDs) and dispersive anisoplanatism. We report on progress in laser guide star (LGS) performance and a real-time online experiment in multi-conjugate AO (MCAO). We discuss ELTs, high-resolution spectroscopy and pupil slicing with and without use of AO. Finally, we present some recent studies of ELT enclosure options.
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| 32. |
- Ardeberg, Arne, et al.
(författare)
-
Science drivers of a 50-m AO telescope
- 2003
-
Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5382:1, s. 37-46
-
Konferensbidrag (refereegranskat)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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| 33. |
- Arran, C., et al.
(författare)
-
Potential to measure quantum effects in recent all-optical radiation reaction experiments
- 2019
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11039
-
Konferensbidrag (refereegranskat)abstract
- The construction of 10 PW class laser facilities with unprecedented intensities has emphasized the need for a thorough understanding of the radiation reaction process. We describe simulations for a recent all-optical colliding pulse experiment, where a GeV scale electron bunch produced by a laser wakefield accelerator interacted with a counter-propagating laser pulse. In the rest frame of the electron bunch, the electric field of the laser pulse is increased by several orders of magnitude, approaching the Schwinger field and leading to substantial variation from the classical Landau-Lifshitz model. Our simulations show how the final electron and photon spectra may allow us to differentiate between stochastic and semi-classical models of radiation reaction, even when there is significant shot-to-shot variation in the experimental parameters. In particular, constraints are placed on the maximum energy spread and shot-to-shot variation permissible if a stochastic model is to be proven with confidence.
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| 34. |
- Auriacombe, Olivier, 1989, et al.
(författare)
-
Oil, water, and ice detection on road surfaces with a millimeter-wave radiometer
- 2020
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11533
-
Konferensbidrag (refereegranskat)abstract
- Passive radiometers are well-known instruments used in the characterization of soil, sea surfaces and remote sensing of the earth atmosphere with satellites or airplanes. The instrument described in this article is a dual-polarised superheterodyne radiometer operating around 93 GHz. It is placed on a structure to measure road surface conditions (ice, water or oil) in a laboratory-controlled environment. This radiometer measures the reflected and emitted radiations from the road surface (asphalt and concrete) and the background temperature, in two orthogonal polarizations (H and V). The difference in the dielectric properties of the ice, oil and water from dry road surface allows to distinguish them efficiently. This kind of technique can be used for road surface recognition in all weather conditions and does not require presence of daylight or other sources of illumination. In this paper, calibration procedures and radiometric characterisations of the radiometer are studied in order to select the best and simpler method to operate the radiometer. It was found that calibrating the radiometer with only one blackbody target or using a table of gain and system noise temperature is sufficiently accurate over a long time to be able to distinguish dry from ice or water covered surfaces. The laboratory results are showing a high difference in the brightness temperature between road surface covered with ice, water or oil and the dry road surface. No ambiguities between those conditions exist but potential limitations could rise, for example if the road surface roughness changes during a measurement. Those promising results validate the potential of using radiometer for road safety and the automotive industry. The presented laboratory measurements are the first step towards the implementation of the instrument into a moving vehicle for alerting drivers ahead of unforeseen dangers. Downloading of the abstract is permitted for personal use only.
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| 35. |
- Aurumskjöld, Marie-Louise, et al.
(författare)
-
An investigation of the iterative reconstruction method iDose(4) on a Philips CT Brilliance 64 using a Catphan 600 phantom
- 2012
-
Ingår i: Medical Imaging 2012: Physics of Medical Imaging. - : SPIE. - 0277-786X .- 1996-756X. ; 8313
-
Konferensbidrag (refereegranskat)abstract
- The number of CT examinations giving a relatively high patient exposure is increasing. It is therefore important to optimize the imaging conditions at these investigations. Many steps have been taken to reduce the radiation doses in CT examinations. Currently much work is related to iterative image reconstruction methods as alternative to the filtered back projection method. The aim of this work was to evaluate quality parameters in images from a CT (Philips Brilliance 64) equipped with the iterative reconstruction method iDose(4) using a Catphan 600 phantom with and without body simulating ring. CT scans using abdomen protocol were taken with various tube currents and tube voltage and keeping collimation and pitch unchanged for all scans. All collected data were reconstructed with different levels of iDose(4) (Level 2, 4, 6) and traditional filtered back projection. Image quality parameters were evaluated using AutoQA Lite (TM) (Version 2.3 2007 Iris QA, LLC). Results from the study shows that the iterative reconstruction method decreases the noise with 15-45% compared with filtered back projection depending on which level of iDose(4) is used. The percentage reduction in noise level is the same with and without body simulating ring. Low contrast was improved with iDose(4) and spatial resolution is only marginally affected by the method of reconstruction. However by reducing the image noise, the detectability can be improved. Our conclusion is that there is great potential to reduce the noise and thereby improve the image quality by using iterative reconstruction methods. This can also be used to lower radiation dose and maintain image quality or improve image quality.
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| 36. |
- Aurumskjöld, Marie-Louise, et al.
(författare)
-
Model based iterative reconstruction IMR gives possibility to evaluate thinner slice thicknesses than conventional iterative reconstruction iDose(4) - a phantom study
- 2015
-
Ingår i: Medical Imaging 2015: Physics of Medical Imaging. - : SPIE. - 1996-756X .- 0277-786X. ; 9412, s. 94124-94124
-
Konferensbidrag (refereegranskat)abstract
- Computed tomography (CT) is one of the most important modalities in a radiological department, which produces images with high diagnostic confidence, but in some cases contributes to a high radiation dose to the patient. The radiation dose can be reduced by the use of advanced image reconstruction algorithms. This study was done on a Philips Brilliance iCT with iterative reconstruction iDose(4) and model-based iterative reconstruction IMR. The purpose was to investigate the effect on the image quality with thin slice images reconstructed with IMR, compared to standard slice thickness reconstructed with iDose(4). Objective measurements of noise and contrast-to-noise ratio were performed using an image quality phantom, an anthropomorphic phantom and clinical cases. Subjective evaluations of low-contrast resolution were performed by observers using an image quality phantom. IMR gives strong noise reduction and enhanced low-contrast and thereby enable selection of thinner slice thickness. Objective evaluation of image noise shows that thin slices reconstructed with IMR provides lower noise than thicker slice images reconstructed with iDose(4). With IMR the slice thickness is of less importance for the noise. With thinner slices the partial volume artefacts becomes less pronounced. In conclusion, we have shown that IMR enables reduction of the slice thickness and at the same time maintain or even reduce the noise level compared to iDose(4) reconstruction with standard slice thickness. This will subsequently result in an improvement of image quality for images reconstructed with IMR.
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| 37. |
- Axelsson, Rebecca, et al.
(författare)
-
Simultaneous digital breast tomosynthesis and mechanical imaging in women recalled from screening - A preliminary analysis
- 2022
-
Ingår i: 16th International Workshop on Breast Imaging, IWBI 2022. - : SPIE. - 0277-786X .- 1996-756X. - 9781510655843 ; 12286
-
Konferensbidrag (refereegranskat)abstract
- We have developed a method for simultaneous tomosynthesis and mechanical imaging, called DBTMI. Mechanical imaging measures the stress distribution over the compressed breast surface. Malignant tissue is usually stiffer than benign, which results in higher stress on the compressed breast and enables to distinguish malignant from benign findings. By combining tomosynthesis and mechanical imaging, we could improve cancer detection accuracy by reducing the number of false positive findings. In this study we have analysed clinical DBTMI data, collected from 52 women from an ongoing pilot study at the Skåne University Hospital, Malmö, Sweden. We measured the range of the average stress over the breast surface, the range of average stress over the location of suspected lesions, and the normalized stress over the lesion location. Preliminary results show that the range of stress over the breast surface was 1.23-5.84 kPa, the range over the lesion location 2.10-10.10 kPa, and the normalized stress 1.12-2.44 over the lesion location. Overall, the local stress over malignant lesions was higher than the average stress over the entire breast surface. This is the first step investigating criteria to distinguish between malignant and benign findings based upon clinical DBTMI data.
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| 38. |
- Ayerden, N.P., et al.
(författare)
-
Design, fabrication and characterization of LVOF-based IR microspectrometers
- 2014
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628410785 ; 9130
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the design, fabrication and characterization of a linear variable optical filter (LVOF) that operates in the infrared (IR) spectral range. An LVOF-based microspectrometer is a tapered-cavity Fabry-Perot optical filter placed on top of a linear array of detectors. The filter transforms the optical spectrum into a lateral intensity profile, which is recorded by the detectors. The IR LVOF has been fabricated in an IC-compatible process flow using a resist reflow and is followed by the transfer etching of this resist pattern into the optical resonator layer. This technique provides the possibility to fabricate a small, robust and high-resolution micro-spectrometer in the IR spectral range directly on a detector chip. In these designs, the LVOF uses thin-film layers of sputtered Si and SiO 2 as the high and low refractive index materials respectively. By tuning the deposition conditions and analyzing the optical properties with a commercial ellipsometer, the refractive index for Si and SiO2 thin-films was measured and optimized for the intended spectral range. Two LVOF microspectrometers, one operating in the 1.8-2.8 μm, and the other in the 3.0-4.5 μm wavelength range, have been designed and fabricated on a silicon wafer. The filters consist of a Fabry-Perot structure combined with a band-pass filter to block the out-of-band transmission. Finally, the filters were fully characterized with an FTIR spectrometer and the transmission curve widening was investigated. The measured transmittance curves were in agreement with theory. The characterization shows a spectral resolution of 35-60 nm for the short wavelength range LVOF and 70 nm for the long wavelength range LVOF, which can be further improved using signal processing algorithms.
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| 39. |
- Bakic, Predrag R., et al.
(författare)
-
Evaluation of a flat fielding method for simultaneous DBT and MI acquisition
- 2020
-
Ingår i: 15th International Workshop on Breast Imaging, IWBI 2020. - : SPIE. - 1996-756X .- 0277-786X. - 9781510638310 ; 11513
-
Konferensbidrag (refereegranskat)abstract
- We are developing a prototype system for simultaneous digital breast tomosynthesis (DBT) and mechanical imaging (MI). MI maps the local pressure distribution during clinical exams, to distinguish breast abnormalities from the normal tissue. Both DBT alone, and MI when combined with digital mammography, have demonstrated the ability to reduce false positives; however, the benefit of combining DBT with MI has not been investigated. A practical limitation in simultaneous DBT and MI is the presence of the MI sensor in DBT images. Metallic elements of the sensor generate noticeable artifacts, which may interfere with clinical analysis. Previously, we shown that the sensor artifacts can be reduced by flat fielding, which combines projections of the sensor acquired with and without the breast. In this paper we evaluate the flat fielding by assessing artifact reduction and visibility of breast abnormalities. Images of a physical anthropomorphic breast phantom were acquired using a clinical wide-angle DBT system. Visual evaluation was performed by experienced medical physicists. Image quality descriptors were calculated in images with and without flat fielding. To evaluate the visibility of abnormalities we estimated the full width at half maximum (FWHM) for calcifications modeled in the phantom. Our preliminary results suggest a substantial reduction of artifacts by flat fielding (on average 83%). Few noticeable artifacts remain near the breast edge, in the reconstructed image with the sensor in focus. We observed a 17% reduction in the FWHM. Future work would include a detailed assessment, and method optimization using virtual trials as a design aid.
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| 40. |
- Baron, P., et al.
(författare)
-
Measurement of stratospheric and mesospheric winds with a submillimeter wave limb sounder: results from JEM/SMILES and simulation study for SMILES-2
- 2015
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628418491 ; 9639, s. Article no. 96390N-
-
Konferensbidrag (refereegranskat)abstract
- Satellite missions for measuring winds in the troposphere and thermosphere will be launched in a near future. There is no plan to observe winds in the altitude range between 30-90 km, though middle atmospheric winds are recognized as an essential parameter in various atmospheric research areas. Sub-millimetre limb sounders have the capability to fill this altitude gap. In this paper, we summarize the wind retrievals obtained from the Japanese Superconducting Submillimeter Wave Limb Emission Sounder (SMILES) which operated from the International Space Station between September 2009 and April 2010. The results illustrate the potential of such instruments to measure winds. They also show the need of improving the wind representation in the models in the Tropics, and globally in the mesosphere. A wind measurement sensitivity study has been conducted for its successor, SMILES-2, which is being studied in Japan. If it is realized, sub-millimeter and terahertz molecular lines suitable to determine line-of-sight winds will be measured. It is shown that with the current instrument definition, line-of-sight winds can be observed from 20 km up to more than 160 km. Winds can be retrieved with a precision better than 5 m s(-1) and a vertical resolution of 2-3 km between 35-90 km. Above 90 km, the precision is better than 10 m s(-1) with a vertical resolution of 3-5 km. Measurements can be performed day and night with a similar sensitivity. Requirements on observation parameters such as the antenna size, the satellite altitude are discussed. An alternative setting for the spectral bands is examined. The new setting is compatible with the general scientific objectives of the mission and the instrument design. It allows to improve the wind measurement sensitivity between 35 to 90 km by a factor 2. It is also shown that retrievals can be performed with a vertical resolution of 1 km and a precision of 5-10 m s(-1) between 50 and 90 km. RAGAM A, 1953, PHYSICAL REVIEW, V92, P1448
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| 41. |
- Barrientos Z, C. M., et al.
(författare)
-
Vertically illuminated TW-UTC photodiodes for terahertz generation
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819491534 ; 8452
-
Konferensbidrag (refereegranskat)abstract
- More efficient and powerful continuous-wave photonic mixers as terahertz sources are motivated by the need of more versatile local oscillators for submillimeter/terahertz receiver systems. Uni-Travelling Carrier (UTC) photodiodes are very prospective candidates for reaching this objective, but so far only have been reported as lumped-elements or as edge-illuminated optical-waveguide travelling-wave (TW) devices. To overcome the associated power limitations of those implementations, we are developing a novel implementation of the UTC photodiodes which combines a traveling-wave photomixer with vertical velocity-matched illumination in a distributed structure. In this implementation called velocity-matched travelling-wave uni-travelling carrier photodiode, it is possible to obtain in-situ velocity matching of the beat-fringes of the two angled laser beams with the submm/THz-wave on the stripline. In this way, minimum frequency roll-off is achieved by tuning the angle between the two laser beams. A first design of these TW-UTC PDs from our Terahertz Photonics Laboratory at University of Chile has been micro-fabricated at the MC2 cleanroom facility at Chalmers Technical University.
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| 42. |
- Barrientos Z, C. M., et al.
(författare)
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Vertically illuminated TW-UTC photodiodes for terahertz generation
- 2010
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819482310 ; 7741
-
Konferensbidrag (refereegranskat)abstract
- More efficient continuous-wave photonic nearinfrared mixers as terahertz sources are investigated with the motivation to develop a universal photonic local oscillator for astronomical submillimeter/terahertz receiver systems. For this, we develop new concepts for vertically illuminated traveling-wave (TW) photomixers, TW Uni-Travelling Carrier (UTC) photodiodes. Device simulation/modeling and optical/terahertz testing is being done in the new terahertz photonics laboratory at the Electrical Engineering Department of the University of Chile, whereas device fabrication is performed at the MC2 cleanroom facility at Chalmers Technical University. We report on first progress in this direction.
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| 43. |
- Batista, P.D., et al.
(författare)
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Acousto-electric single-photon detector
- 2007
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6583, s. 658304-
-
Tidskriftsartikel (refereegranskat)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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| 44. |
- Baveja, P. P., et al.
(författare)
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Impact of photon lifetime on thermal rollover in 850-nm high-speed VCSELs
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276
-
Konferensbidrag (refereegranskat)abstract
- We present an empirical thermal model for VCSELs based on extraction of temperature dependence of macroscopic VCSEL parameters from CW measurements. We apply our model to two, oxide-confined, 850-nm VCSELs, fabricated with a 9-mu m inner-aperture diameter and optimized for high-speed operation. We demonstrate that for both these devices, the power dissipation due to linear heat sources dominates the total self-heating. We further show that reducing photon lifetime down to 2 ps drastically reduces absorption heating and improves device static performance by delaying the onset of thermal rollover. The new thermal model can identify the mechanisms limiting the thermal performance and help in formulating the design strategies to ameliorate them.
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| 45. |
- Bejnö, Anna, et al.
(författare)
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Artificial intelligence together with mechanical imaging in mammography
- 2020
-
Ingår i: 15th International Workshop on Breast Imaging, IWBI 2020. - : SPIE. - 0277-786X .- 1996-756X. - 9781510638310 ; 11513
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Konferensbidrag (refereegranskat)abstract
- Artificial intelligence (AI) applications are increasingly seeing use in breast imaging, particularly to assist in or automate the reading of mammograms. Another novel technique is mechanical imaging (MI) which estimates the relative stiffness of suspicious breast abnormalities by measuring the distribution of pressure on the compressed breast. This study investigates the feasibility of combining AI and MI information in breast imaging to provide further diagnostic information. Forty-six women recalled from screening were included in the analysis. Mammograms with findings scored on a suspiciousness scale by an AI tool, and corresponding pressure distributions were collected for each woman. The cases were divided into three groups by diagnosis; biopsy-proven cancer, biopsy-proven benign and non-biopsied, very likely benign. For all three groups, the relative increase of pressure at the location of the finding marked most suspicious by the AI software was recorded. A significant correlation between the relative pressure increase at the AI finding and the AI score was established in the group with cancer (p=0.043), but neither group of healthy women showed such a correlation. This study suggests that AI and MI indicate independent markers for breast cancer. The combination of these two methods has the potential to increase the accuracy of mammography screening, but further research is needed.
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| 46. |
- Benckert, Lars, et al.
(författare)
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Measuring 3-D displacement of a surface using the white light speckle technique
- 1986
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 599, s. 207-210
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Tidskriftsartikel (refereegranskat)abstract
- When measuring in plane surface deformation using white light speckle photography, errors will arise if an out of plane displacement is present. Here it is shown that stereoscopic photography resolves this problem and makes the measurement of true in plane displacements possible. A rigid body translation is also introduced to determine unambiguously the direction of the displacement
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| 47. |
- Bengtsson, Tomas, 1983, et al.
(författare)
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Variational Optical Flow Estimation for Images with Spectral and Photometric Sensor Diversity
- 2015
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628415582 ; 9443, s. Art. no. 94431U-
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Konferensbidrag (refereegranskat)abstract
- Motion estimation of objects in image sequences is an essential computer vision task. To this end, optical flow methods compute pixel-level motion, with the purpose of providing low-level input to higher-level algorithms and applications. Robust flow estimation is crucial for the success of applications, which in turn depends on the quality of the captured image data. This work explores the use of sensor diversity in the image data within a framework for variational optical flow. In particular, a custom image sensor setup intended for vehicle applications is tested. Experimental results demonstrate the improved flow estimation performance when IR sensitivity or flash illumination is added to the system.
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| 48. |
- Berbyuk, Viktor, 1953, et al.
(författare)
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Towards early ice detection on wind turbine blades using acoustic waves
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819499899 ; 9063, s. 90630F-1 - 90630F-11-
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Konferensbidrag (refereegranskat)abstract
- The study focuses on the early detection of ice using controlled acoustic waves propagating in the wind turbine blades.An experimental set-up with a cold climate chamber, a composite test object used in turbine blades and equipment for glaze and rime ice production has been developed. Controlled acoustic waves are generated by magnetostrictiveTerfenol-D based actuator. The propagation of three orthogonally polarized acoustic waves was studied by means of 6 accelerometers positioned, 3 each, in 2 holders on the 8 m long composite test object. The results show that for the considered composite test object the formation of ice, the ice mass, icing areas and the temperature have a significant influence on controlled acoustic waves propagation w.r.t. Fourier transform, amplitude attenuation and RMS values as indicators concluding that the proposed acoustic wave technique is a promising approach for ice detection.
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| 49. |
- Berbyuk, Viktor, 1953
(författare)
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Vibration energy harvesting using Galfenol based transducer
- 2013
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 8688, s. 86881F-1 - 86881F-12-
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Konferensbidrag (refereegranskat)abstract
- In this paper the novel design of Galfenol based vibration energy harvester is presented. The device uses Galfenol roddiameter 6.35 mm and length 50mm, polycrystalline, production grade, manufactured by FSZM process by ETREMAProduct Inc. For experimental study of the harvester, the test rig was developed. It was found by experiment that forgiven frequency of external excitation there exist optimal values of bias and pre-stress which maximize generatedvoltage and harvested power. Under optimized operational conditions and external excitations with frequency 50Hz thedesigned transducer generates about 10 V and harvests about 0,45 W power. Within the running conditions, the Galfenol rod power density was estimated to 340mW/cm3. The obtained results show high practical potential of Galfenol based sensors for vibration-to-electrical energy conversion, structural health monitoring, etc.
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| 50. |
- Bickham, S., et al.
(författare)
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Low cutoff G.657-compatible fiber for data center interconnects operating in the 1064 and 1310 nm windows
- 2020
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11286
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Konferensbidrag (refereegranskat)abstract
- Optical interconnects in data centers have traditionally used 850 nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) in combination with multimode fiber, having a reach up to 100 m in length. Longer links typically use standard single-mode fiber in conjunction with either InP-based edge-emitting lasers or silicon photonic transmitters operating in the 1310 nm or 1550 nm window. Single-mode GaAs-based VCSELs operating at 1064 nm offer another path for achieving longer system reach. Potential advantages of these VCSELs include better power efficiency, modulation speeds reaching 50 Gbps and large-scale fabrication volumes. The longer wavelength is also beneficial due to the lower attenuation and chromatic dispersion of optical fibers at that wavelength. However, one practical issue for single-mode transmission is that the G.657 standard for single-mode fiber requires that the 22-meter cable cutoff wavelength be less than 1260 nm, and these fibers are typically few-moded at 1064 nm. The large differences between the group velocities of the LP01 and LP11 modes can lead to degradation of the system performance due to multi-path interference if the higher order modes are present. To resolve this quandary, we have designed and validated the performance of a new optical fiber which is single-moded at wavelengths less than 1064 nm, but also has G.657-compliant mode field diameter and dispersion characteristics that enable it to be used in the 1310 nm window.
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