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  • 1. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Measurement of event-plane correlations in root s(NN)=2.76 TeV lead-lead collisions with the ATLAS detector2014In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 90, no 2, 024905- p.Article in journal (Refereed)
    Abstract [en]

    A measurement of event-plane correlations involving two or three event planes of different order is presented as a function of centrality for 7 mu b(-1) Pb + Pb collision data at v root s(NN) = 2.76 TeV, recorded by the ATLAS experiment at the Large Hadron Collider. Fourteen correlators are measured using a standard event-plane method and a scalar-product method, and the latter method is found to give a systematically larger correlation signal. Several different trends in the centrality dependence of these correlators are observed. These trends are not reproduced by predictions based on the Glauber model, which includes only the correlations from the collision geometry in the initial state. Calculations that include the final-state collective dynamics are able to describe qualitatively, and in some cases also quantitatively, the centrality dependence of the measured correlators. These observations suggest that both the fluctuations in the initial geometry and the nonlinear mixing between different harmonics in the final state are important for creating these correlations in momentum space.

  • 2. Abeywickrama, Sandu
    et al.
    Furdek, Marija
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wong, Elaine
    Protecting core networks with dual-homing: A study on enhanced network availability, resource efficiency, and energy-savings2016In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 381, 327-335 p.Article in journal (Refereed)
    Abstract [en]

    Core network survivability affects the reliability performance of telecommunication networks and remains one of the most important network design considerations. This paper critically examines the benefits arising from utilizing dual-homing in the optical access networks to provide resource-efficient protection against link and node failures in the optical core segment. Four novel, heuristic-based RWA algorithms that provide dedicated path protection in networks with dual-homing are proposed and studied. These algorithms protect against different failure scenarios (i.e. single link or node failures) and are implemented with different optimization objectives (i.e., minimization of wavelength usage and path length). Results obtained through simulations and comparison with baseline architectures indicate that exploiting dual-homed architecture in the access segment can bring significant improvements in terms of core network resource usage, connection availability, and power consumption.

  • 3. Abrahamsson, S.
    et al.
    Blom, Hans
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Agostinho, A.
    Jans, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Jost, A.
    Müller, M.
    Nilsson, Linnea
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Bernhem, K.
    Lambert, T. J.
    Heintzmann, R.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Multifocus structured illumination microscopy for fast volumetric super-resolution imaging2017In: Biomedical Optics Express, ISSN 2156-7085, E-ISSN 2156-7085, Vol. 8, no 9, 4135-4140 p., #294866Article in journal (Refereed)
    Abstract [en]

    We here report for the first time the synergistic implementation of structured illumination microscopy (SIM) and multifocus microscopy (MFM). This imaging modality is designed to alleviate the problem of insufficient volumetric acquisition speed in superresolution biological imaging. SIM is a wide-field super-resolution technique that allows imaging with visible light beyond the classical diffraction limit. Employing multifocus diffractive optics we obtain simultaneous wide-field 3D imaging capability in the SIM acquisition sequence, improving volumetric acquisition speed by an order of magnitude. Imaging performance is demonstrated on biological specimens.

  • 4.
    Abramson, Nils
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics.
    Article may have left false impression that light-in-flight method is new2008In: Laser Focus World, ISSN 1043-8092, Vol. 44, no 4, 10-10 p.Article in journal (Other academic)
  • 5.
    Abramson, Nils
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics.
    FEMTOSECOND IMAGING Motion picture of short pulses2011In: Nature Photonics, ISSN 1749-4885, Vol. 5, no 7, 389-390 p.Article in journal (Refereed)
  • 6.
    Abramson, Nils H.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics.
    Optical resolution and the duality of light2008In: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 47, no 19, D1-D5 p.Article in journal (Refereed)
    Abstract [en]

    For 15 years, lensless microscopes have been constructed based on the use of holography, a digital CCD detector, and a computer for image reconstruction by use of, e.g., Fourier transformation. Thus, no lens is involved and therefore the conventional resolution limit of half the wavelength no longer applies. Instead of being limited by the wavelength, the resolution is in this case limited by how exact one can measure the phases of the light. It is remarkable that the interference-limited resolution is approximately 0.01X, whereas the diffraction-limited resolution is only of the order of 0.5X. It is my hope that by combining these two techniques it will be possible to increase the magnification in optical systems by at least an order of magnitude. The calculations at so indicate that information does not necessarily decrease with distance.

  • 7.
    Adamsson, Carl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Dryout and Power Distribution Effects in Boiling Water Reactors2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Film flow measurements at several axial positions in round pipes with variousaxial power distributions are presented for conditions corresponding to normaloperation of a BWR. It is confirmed that the film flow rate approaches zero atthe onset of dryout. Selected phenomenological models of annular two-phaseflow are shown to reasonably reproduce the measurements. It is concluded thatmodels are in better agreement with measurements if terms corresponding topossible boiling induced entrainment are excluded.

    A method to perform film flow analysis in subchannels as a post-processto a standard two-field subchannel code is suggested. It is shown that thisapproach may yield accurate prediction of dryout power in rod bundles to alow computational cost and that the influence of the power distribution is wellpredicted by the model.

  • 8.
    Adamsson, Carl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Measurements of Film Flow Rate in Heated Tubes with Various Axial Power Distributions2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Measurements of film mass flow rate for annular, diabatic steam-water flow in tubes are presented. The measurements were carried out with four axial power distributions and at several axial positions at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m2s. The results show that the influence of the axial power distribution on the dryout power corresponds to a consistent tendency in the film flow rate and that the film tends to zero when dryout is approached. Furthermore it is demonstrated that two selected phenomenological models of annular flow well predict the present data. A model for additional entrainment due to boiling is shown to degrade the predictions.

  • 9.
    Adamsson, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Eperimental Investigation of the Liquid Film for Annular Flow in a Tube with Various Axial Power Distributions2005In: NURETH 11, Avignon, France, October 2–6, 2005, 2005Conference paper (Refereed)
    Abstract [en]

    This paper was published when the measurements with non-uniform powerdistribution were still ongoing. Therefore only the measurements with uniformand top-peaked power profiles were included. The paper compares the measured data with deposition and entrainmentmodels by Hewitt & Govan (1990) and Okawa et al. (2003). These models are also discussed in Sections 4.2.1 and 4.2.2. The issue of a correct boundarycondition at the onset of annular flow was avoided by starting the integrationof the film flow model from the most upstream measurement point. In this way the net mass exchange rate (deposition less entrainment) could be studied without any initial bias from the boundary condition.The entrainment correlation proposed by Okawa et al. (2003) included a heat flux dependent term to account for boiling entrainment (Section 4.2.2). Paper 2 concludes that the model agrees better with measurements if this term is omitted. The result suggests that boiling entrainment may not be an important effect at the investigated conditions.

  • 10.
    Adamsson, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Film flow measurements for high-pressure diabatic annular flow in tubes with various axial power distributions2006In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 236, no 23, 2485-2493 p.Article in journal (Refereed)
    Abstract [en]

    Measurements of film flow rates in diabatic annular flow in tubes with various axial power distributions were carried out in the high-pressure two-phase flow loop at the Royal Institute of Technology (KTH), Sweden. The measurements were performed at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m(2)s. Four different axial power distributions were used and the film mass flow was measured at 7 axial locations for each set of boundary conditions. The results show that the outlet peaked distribution gives less film than the inlet peaked one. This result is consistent with well known trends from measurements of dryout power. The measurements also show that the film flow at the onset of dryout is very small at investigated conditions in agreement with earlier studies. Finally it is shown that the present data is well predicted by two selected phenomenological models of annular flow.

  • 11.
    Adamsson, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Influence of Axial Power Distribution on Dryout: Film-Flow Models and Experiments2010In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 240, no 6, 1495-1505 p.Article in journal (Refereed)
    Abstract [en]

    The influence of axial power distributions on dryout occurrence in nuclear fuel assemblies has been studied extensively for several decades. Even though it is well known that axial power shapes which may significantly vary in nuclear reactors during their operation significantly change the dryout power level, this particular influence is rather difficult to capture with current correlations. In this paper it is shown that this influence can be captured using a phenomenological liquid film model coupled to a standard sub-channel code. The model has been applied to various geometries, including a round pipe, as well as 5 x 5 and 8 x 8 fuel rod assemblies, and highly accurate predictions have been obtained.

  • 12.
    Adamsson, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Henryk, Anglart
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Measurements of the Liquid Film Flow Rate in High Pressure Annular Flow with Various Axial Power Distributions2005In: HEAT 2005, Gdansk, Poland, June 26–30, 2005, 2005Conference paper (Refereed)
    Abstract [en]

    This paper presents film flow measurement technique and the results with uniform power distribution. Based on these measurements it is possible to estimate the critical film thickness. The measured film thickness was plotted versus steam quality and slightlyextrapolated up to the measured critical steam quality. The conclusions werein line with Hewitt et al. (1965), i.e. that the critical film thickness is insignificantly small. This does not contradict e.g. Ueda & Isayama (1981) since the conditions were not the same, but for the flow conditions and heat fluxes that are typical for BWR operation it was concluded that the critical film thickness is, for practical purposes, zero.

  • 13.
    Adamsson, Carl
    et al.
    Westinghouse Electric Sweden.
    Le Corre, J. M.
    Westinghouse Electric Sweden.
    Modeling and Validation of a Mechanistic Tool (MEFISTO) for the Prediction of Critical Power in BWR Fuel Assemblies2011In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 241, no 8, 2843-2858 p.Article in journal (Refereed)
    Abstract [en]

    Westinghouse is currently developing the MEFISTO code with the main goal to achieve fast, robust, practical and reliable prediction of steady-state dryout Critical Power in Boiling Water Reactor (BWR) fuel bundle based on a mechanistic approach. A computationally efficient simulation scheme was used to achieve this goal, where the code resolves all relevant field (drop, steam and multi-film) mass balance equations, within the annular flow region, at the sub-channel level while relying on a fast and robust two-phase (liquid/steam) sub-channel solution to provide the cross-flow information. The MEFISTO code can hence provide highly detailed solution of the multi-film flow in BWR fuel bundle while enhancing flexibility and reducing the computer time by an order of magnitude as compared to a standard three-field sub-channel analysis approach. Models for the numerical computation of the one-dimensional field flowrate distributions in an open channel (e.g. a sub-channel), including the numerical treatment of field cross-flows, part-length rods, spacers grids and post-dryout conditions are presented in this paper. The MEFISTO code is then applied to dryout prediction in BWR fuel bundle using VIPRE-W as a fast and robust two-phase sub-channel driver code. The dryout power is numerically predicted by iterating on the bundle power so that the minimum film flowrate in the bundle reaches the dryout criteria. Predicted dryout powers (including trends with flow, pressure, inlet subcooling and power distribution) and predicted dryout locations (both axial and radial) are compared to experimental results, using the entire Westinghouse SVEA-96 Optima3 dryout database, and are shown to yield excellent results.

  • 14. Agate, B.
    et al.
    Rafailov, E. U.
    Sibbett, W.
    Saltiel, S. M.
    Koynov, K.
    Tiihonen, Mikael
    KTH, Superseded Departments, Physics.
    Wang, Shunhua
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Battle, P.
    Fry, T.
    Roberts, T.
    Noonan, E.
    Portable ultrafast blue light sources designed with frequency doubling in KTP and KNbO32004In: IEEE Journal of Selected Topics in Quantum Electronics, ISSN 1077-260X, E-ISSN 1558-4542, Vol. 10, no 6, 1268-1276 p.Article in journal (Refereed)
    Abstract [en]

    We demonstrate an effective means of achieving compact, truly portable, and entirely self-contained ultrafast blue light sources. Using a variety of nonlinear media to achieve simple second-harmonic generation of a femtosecond Cr:LiSAF laser, we investigate the relative merits of aperiodically poled bulk and waveguide nonlinear crystals in comparison to periodically poled structures. Such a compact and convenient source of ultrashort laser pulses in the blue spectral region could be of great interest for on-site applications spanning a host of disciplines, such as biomedical imaging, optical micromanipulation, and high-resolution spectroscopy.

  • 15. Aggerstam, Thomas
    et al.
    Lovqvist, Anita
    Stevens, Renaud
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Jonsson, Stefan
    Marcks von Würtemberg, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Dubois, Mardjan
    Ghisoni, Marco
    Selectively oxidized vertical-cavity surface-emitting lasers for high-speed data communication2001In: Proc. SPIE 4286, SPIE's Optoelectronics 2001, Photonics West, San Jose, US, Bellingham, WA, ETATS-UNIS: Society of Photo-Optical Instrumentation Engineers , 2001, Vol. 4286, 96- p.Conference paper (Refereed)
    Abstract [en]

    MITEL Semiconductor is developing the next generation low cost, high performance transceivers for data communication. The increasing quantity of data being transferred over the Internet demands very high capacity interconnects. A low cost, high-performance alternative is the use of parallel fiber interconnects where the light is, for example, coupled into a 12-channel fiber-ribbon. Parallel interconnects require good uniformity in order to reduce escalating costs and complexity. In this paper we report on the static and the modulation properties of 850nm multimode oxide VCSELs for use in such Gb/s transceiver system. Static power-current-voltage characteristics with good uniformity were obtained for different structures, with threshold currents down to sub-mA. A maximum small signal 3-dB bandwidth of 10 GHz and a modulation current efficiency up to 8.4 GHz/√[mA] were measured. Single channel results are presented for VCSELs operated at data rates from 2.5-10Gb/s.

  • 16. Ahlfeldt, H.
    et al.
    Holm, J.
    Lindgren, S.
    Backlin, L.
    Vieider, C.
    Klinga, T.
    Kerzar, B.
    Nilsson, M.
    Svensson, M.
    Nilsson, S.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    20 GHz bandwidth of lasers flip-chip-mounted on microstructured carriers with integrated electrical waveguides1998In: Optical Communication, 1998. 24th European Conference on, 1998, Vol. 1, 205-206 p.Conference paper (Refereed)
    Abstract [en]

    A flip-chip-mounting scheme for high-speed lasers has been realised. The mounting scheme involves a microstructured silicon carrier with integrated membrane transmission lines and self-aligning solder bumps

  • 17.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Iridium catalyzed hydrogenation of CO2 under basic conditions-Mechanistic insight from theory2010In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, Vol. 324, no 1-2, 3-8 p.Article in journal (Refereed)
    Abstract [en]

    The iridium(III) catalyzed hydrogenation of carbon dioxide under basic conditions was studied with density functional theory. It was found that the insertion of CO2 into an Ir-H bond proceeds via a two-step mechanism. The rate-limiting step was calculated to be the regeneration of the iridium(III) trihydride intermediate, and the overall barrier for the reaction was calculated to 26.1 kcal mol(-1). The formation of the iridium trihydride proceeds via formation of a cationic Ir(H)(2)(H-2) complex at which the base abstracts a proton from the dihydrogen ligand. (C) 2010 Elsevier B.V. All rights reserved.

  • 18.
    Ahmed, J
    et al.
    KTH.
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Spadaro, S
    Enhancing restoration performance using service relocation in PCE-based resilient optical clouds2014In: Conference on Optical Fiber Communication, Technical Digest Series, 2014Conference paper (Refereed)
    Abstract [en]

    This paper investigates the benefits of dynamic restoration with service relocation in resilient optical clouds. Results from the proposed optimization model show that service availability can be significantly improved by allowing a few service relocations.

  • 19.
    Ako, Thomas
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Design of invisibility cloaks with an open tunnel2010In: Optics Express, ISSN 1094-4087, Vol. 18, no 26, 27060-27066 p.Article in journal (Refereed)
    Abstract [en]

    In this paper we apply the methodology of transformation optics for design of a novel invisibility cloak which can possess an open tunnel. Such a cloak facilitates the insertion (retrieval) of matter into (from) the cloak's interior without significantly affecting the cloak's performance, overcoming the matter exchange bottleneck inherent to most previously proposed cloak designs. We achieve this by applying a transformation which expands a point at the origin in electromagnetic space to a finite area in physical space in a highly anisotropic manner. The invisibility performance of the proposed cloak is verified by using full-wave finite-element simulations. (C) 2010 Optical Society of America

  • 20. Akram, N. M.
    et al.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Experimental evaluation of carrier transport, gain, T0 and chirp of 1.55 mu;m MQW structures with different barrier compositions2005In: Optical Communication, 2005. ECOC 2005. 31st European Conference on, 2005, Vol. 2, 297-298 p.Conference paper (Refereed)
    Abstract [en]

    Direct carrier transport measurements were performed for different InGaAsP/InGaAlAs MQW test structures. Shallow InGaAlAs barrier QW showed faster carrier transport. Semi-insulating regrown FP lasers with InGaAlAs barrier QW showed improved high temperature operation, modal gain, differential modal gain and chirp.

  • 21.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chacinski, Marek
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Experimental characterization of high-speed 1.55 mu m buried heterostructure InGaAsP/InGaAlAs quantum-well lasers2009In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, Vol. 26, no 2, 318-327 p.Article in journal (Refereed)
    Abstract [en]

    Detailed experimental characterization is performed for 1550 nm semi-insulating regrown buried heterostructure Fabry-Perot (FP) lasers having 20 InGaAsP/InGaAlAs strain-balanced quantum wells (QWs) in the active region. Light-current-voltage performance, electrical impedance, small-signal response below and above threshold, amplified spontaneous emission spectrum below threshold and relative intensity noise spectrum are measured. Different laser parameters such as external differential quantum efficiency eta(d), background optical loss alpha(i), K-factor, D-factor, characteristic temperature T-0, differential gain dg/dn, gain-compression factor epsilon, carrier density versus current, differential carrier lifetime tau(d), optical gain spectrum below threshold, and chirp parameter alpha are extracted from these measurements. The FP lasers exhibited a high T-0 (78-86.5 degrees C) and very high-resonance frequency (23.7 GHz). The results indicate that appropriately designed lasers having a large number of InGaAsP well/InGaAlAs barrier QWs with shallow valence-band discontinuity can be useful for un-cooled high-speed direct-modulated laser applications.

  • 22.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chacinski, Marek
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    High-Speed Performance of 1.55 µm Buried Hetero-Structure Lasers with 20 InGaAsP/InGaAlAs Quantum-Wells2006In: 2006 European Conference on Optical Communications Proceedings, ECOC 2006, IEEE , 2006, 1-2 p.Conference paper (Refereed)
    Abstract [en]

    1550 nm re-grown FP lasers having 20 InGaAsP/InGaAlAs strain-balanced QWs exhibit low threshold current density, high T0 (78.0 #x000B0;C) and high resonance frequency (24 GHz) indicating that a large number of shallow barrier QWs are attractive for un-cooled high-speed direct-modulation applications.

  • 23.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Silfvenius, Christofer
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Design optimization of InGaAsP-InGaAlAs 1.55 mu;m strain-compensated MQW lasers for direct modulation applications2004In: Indium Phosphide and Related Materials, 2004. 16th IPRM. 2004 International Conference on, IEEE , 2004, 418-421 p.Conference paper (Refereed)
    Abstract [en]

    A comprehensive simulation study of InGaAsP (well)/InGaAlAs(barrier) 1.55 mu;m strain-compensated MQW lasers is presented. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and strain of the barriers and p-doping in the active region. Some preliminary results are also presented for the manufactured lasers using these QWs indicating a good material platform.

  • 24. Alessi, D
    et al.
    Martz, Dale
    Colorado State Univ, Engn Res Ctr Extreme Ultraviolet Sci & Technol.
    Wang, Y
    Berrill, M
    Luther, B M
    Rocca, J J
    Gain-saturated 10.9 nm tabletop laser operating at 1 Hz repetition rate2010In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 35, no 3, 414-6 p.Article in journal (Refereed)
    Abstract [en]

    We report the demonstration of a gain-saturated 10.9 nm tabletop soft x-ray laser operating at 1 Hz repetition rate. Lasing occurs by collisional electron impact excitation in the 4dS01-->4pP11 transition of nickel-like Te in a line-focus plasma heated by a chirped-pulse-amplification Ti:sapphire laser. With an average power of 1muW and pulse energy up to approximately 2microJ, this laser extends the ability to conduct tabletop laser experiments to a shorter wavelength.

  • 25. Alessi, D.
    et al.
    Wang, Y.
    Luther, B. M.
    Yin, L.
    Martz, D. H.
    epartment of Electrical and Computer Engineering, Colorado State University, Fort Collins, Colorado.
    Woolston, M. R.
    Liu, Y.
    Berrill, M.
    Rocca, J. J.
    Efficient Excitation of Gain-Saturated Sub-9-nm-Wavelength Tabletop Soft-X-Ray Lasers and Lasing Down to 7.36 nm2011In: PHYSICAL REVIEW X, ISSN 2160-3308, Vol. 1, no 2Article in journal (Refereed)
    Abstract [en]

    We have demonstrated the efficient generation of sub-9-nm-wavelength picosecond laser pulses of microjoule energy at 1-Hz repetition rate with a tabletop laser. Gain-saturated lasing was obtained at λ=8.85  nm in nickel-like lanthanum ions excited by collisional electron-impact excitation in a precreated plasma column heated by a picosecond optical laser pulse of 4-J energy. Furthermore, isoelectronic scaling along the lanthanide series resulted in lasing at wavelengths as short as λ=7.36  nm. Simulations show that the collisionally broadened atomic transitions in these dense plasmas can support the amplification of subpicosecond soft-x-ray laser pulses.

  • 26.
    Almlöf, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Quantum error correction2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Quantum error correction is the art of protecting quantum states from the detrimental influence from the environment. To master this art, one must understand how the system interacts with the environment and gives rise to a full set of quantum phenomena, many of which have no correspondence in classical information theory. Such phenomena include decoherence, an effect that in general destroys superpositions of pure states as a consequence of entanglement with the environment. But decoherence can also be understood as “information leakage”, i.e., when knowledge of an encoded code block is transferred to the environment. In this event, the block’s information or entanglement content is typically lost.

    In a typical scenario, however, not all types of destructive events are likely to occur, but only those allowed by the information carrier, the type of interaction with the environment, and how the environment “picks up” information of the error events. These characteristics can be incorporated into a code, i.e., a channel-adapted quantum error-correcting code.

    Often, it is assumed that the environment’s ability to distinguish between error events is small, and I will denote such environments “memory-less”. But this assumption is not always valid, since the ability to distinguish error events is related to the temperature of the environment, and in the particular case of information coded onto photons, kBTR «ℏω typically holds, and one must then assume that the environment has a “memory”. In the thesis I describe a short quantum error-correction code adapted for photons interacting with a “cold” reservoir, i.e., a reservoir which continuously probes what error occurred in the coded state.

    I also study other types of environments, and show how to distill meaningful figures of merit from codes adapted for these channels, as it turns out that resource-based figures reflecting both information and entanglement can be calculated exactly for a well-studied class of channels: the Pauli channels. Starting from these resource-based figures, I establish the notion of efficiency and quality and show that there will be a trade-off between efficiency and quality for short codes. Finally I show how to incorporate, into these calculations, the choices one has to make when handling quantum states that have been detected as incorrect, but where no prospect of correcting them exists, i.e., so-called detection errors.

  • 27.
    Almlöf, Jonas
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Quantum Electronics and Quantum Optics, QEO.
    Björk, Gunnar G. E.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Quantum Electronics and Quantum Optics, QEO.
    A short and efficient error correcting code for polarization coded photonic qubits in a dissipative channel2011In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 284, no 1, 550-554 p.Article in journal (Refereed)
    Abstract [en]

    We propose a short and efficient non-degenerate quantum error correcting code that is adapted for qubits encoded on two orthogonal, single-photon states (e.g., horizontally and vertically polarized) subject to a dissipative channel. The proposed code draws its strength from the fact that it is adapted to the physical characteristics of the information-carrying basis states under the action of the channel. The code combines different energy manifolds and consists of only 3 spatio-temporal modes and on average 2 photons per code word.

  • 28.
    Almlöf, Jonas
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Björk, Gunnar G. E.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Fidelity as a figure of merit in quantum error correction2013In: Quantum information & computation, ISSN 1533-7146, Vol. 13, no 1-2, 0009-0020 p.Article in journal (Refereed)
    Abstract [en]

    We discuss the fidelity as a figure of merit in quantum error correction schemes. We show that when identifiable but uncorrectable errors occur as a result of the action of the channel, a common strategy that improves the fidelity actually decreases the transmitted mutual information. The conclusion is that while the fidelity is simple to calculate and therefore often used, it is perhaps not always a recommendable figure of merit for quantum error correction. The reason is that while it roughly speaking encourages optimisation of the "mean probability of success", it gives no incentive for a protocol to indicate exactly where the errors lurk. For small error probabilities, the latter information is more important for the integrity of the information than optimising the mean probability of success.

  • 29. Alonso, M. A.
    et al.
    Setala, T.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Optimal pulses for arbitrary dispersive media2011In: Journal of the European Optical Society - Rapid Publications, ISSN 1990-2573, Vol. 6, 11035- p.Article in journal (Refereed)
    Abstract [en]

    A variational procedure is given for finding the pulses for which the initial temporal rms width and the rate of increase of this width are jointly minimized for propagation in non-absorbing media with arbitrary dispersive properties. We show that, while in linearly dispersive media the optimal pulses are Gaussian, in other situations such as a hollow metallic waveguide or for purely cubic dispersion departures from Gaussian behavior become evident. An interpretation of the results in terms of suitable phase-space representations is also given.

  • 30. Alsmeyer, H
    et al.
    Albrecht, G
    Meyer, L
    Hafner, W
    Journeau, C
    Fischer, M
    Hellman, S
    Eddi, M
    Allelein, H J
    Burger, M
    Sehgal, Balraj
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Koch, M K
    Alkan, Z
    Petrov, J B
    Gaune-Escard, M
    Altstadt, E
    Bandini, G
    Ex-vessel core melt stabilization research (ECOSTAR)2005In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 235, no 2-4, 271-284 p.Article in journal (Refereed)
    Abstract [en]

    The project on ex-vessel core melt stabilization research (ECOSTAR) started in January 2000 to be concluded by end of 2003. The project is performed by 14 partner institutions from five European countries and involves a large number of experiments with low- and high-temperature simulant melts and real corium at different scales. Model development and scaling analysis allows application of the research results to existing and to future LWRs in the area of reactor design and accident mitigation. The project is oriented toward the analysis and mitigation of severe accident sequences that could occur in the ex-vessel phase of a postulated core melt accident. The issues are: (1) the release of melt form the pressure vessel, (2) the transfer and spreading of the melt on the basement, (3) the analysis of the physical-chemical processes that are important for corium behavior especially during concrete erosion with onset of solidification, and (4) stabilization of the melt by cooling through direct water contact. The results achieved so far resolve a number of important issues: the amount of melt that could be transferred at RPV failure from the RPV into the containment can be substantially reduced by lowering the residual pressure in the primary circuit. It is found that melt dispersion also strongly depends on the location of the RPV failure, and that lateral failure results in substantially less melt dispersion. During melt release, the impinging melt jet could erode parts of the upper basement surface. Jet experiments and a derived heat transfer relation allow estimation of its contribution to concrete erosion. Spreading of the corium melt on the available basement surface is an important process, which defines the initial conditions for concrete attack or for the efficiency of cooling in case of water contact, respectively. Validation of the spreading codes based on a large-scale benchmark experiment is underway and will allow determination of the initial conditions, for which a corium melt can be assumed to spread homogeneously over the available surface. Experiments with UO(2)-based corium melts highlight the role of phase segregation during onset of melt solidification and during concrete erosion. To cool the spread corium melt, the efficacy of top flooding and bottom flooding is investigated in small-scale and in large-scale experiments, supported by model developments. Project assessment is continuing to apply the results to present and future reactors.

  • 31.
    Alvarez Ruiz, Jesus
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Melero-Garcia, Emilio
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kivimäki, Antti
    Coreno, M.
    Erman, Peter
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Richter, R.
    Synchrotron radiation induced fluorescence spectroscopy of SF62005In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 38, 387- p.Article in journal (Refereed)
    Abstract [en]

    The fluorescence of gaseous SF6 was investigated after excitation with 25-80eV synchrotron radiation photons. The total UV-Vis-near IR fluorescence yield was recorded and interpreted in terms of inner valence excitations/ionizations and double excitations in SF6. Dispersed fluorescence measurements in the 400-1000 nm spectral range reveal excited S, S+, F and F+ fragments as solely responsible for the emission. The fluorescence intensity of some of the observed atomic transitions was monitored as a function of the excitation energy. Single, double and triple excitations as well as direct ionizations and shake-ups are proposed as the triggering processes responsible for the creation of the emitting fragments.

  • 32. Amaya, Andrew J.
    et al.
    Pathak, Harshad
    Modak, Viraj P.
    Laksmono, Hartawan
    Loh, N. Duane
    Sellberg, Jonas A.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Sierra, Raymond G.
    McQueen, Trevor A.
    Hayes, Matt J.
    Williams, Garth J.
    Messerschmidt, Marc
    Boutet, Sebastien
    Bogan, Michael J.
    Nilsson, Anders
    Stan, Claudiu A.
    Wyslouzil, Barbara E.
    How Cubic Can Ice Be?2017In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 8, no 14, 3216-3222 p.Article in journal (Refereed)
    Abstract [en]

    Using an X-ray laser, we investigated the crystal structure of ice formed by homogeneous ice nucleation in deeply supercooled water nanodrops (r approximate to 10 nm) at similar to 225 K The nanodrops were formed by condensation of vapor in a supersonic nozzle, and the ice was probed within 100 mu s of freezing using femtosecond wide-angle X-ray scattering at the Linac Coherent Light Source free-electron X-ray laser. The X-ray diffraction spectra indicate that this ice has a metastable, predominantly cubic structure; the shape of the first ice diffraction peak suggests stacking-disordered ice with a cubicity value, chi, in the range of 0.78 +/- 0.05. The cubicity value determined here is higher than those determined in experiments with micron-sized drops but comparable to those found in molecular dynamics simulations. The high cubicity is most likely caused by the extremely low freezing temperatures and by the rapid freezing, which occurs on a similar to 1 mu s time scale in single nanodroplets.

  • 33. Andersson, J. Y.
    et al.
    Hoglund, L.
    Noharet, B.
    Wang, Q.
    Ericsson, P.
    Wissmar, Stanley
    Asplund, C.
    Malm, H.
    Martijn, H.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Gustafsson, Oscar
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hellström, S.
    Radamson, Henry
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Holtz, P. O.
    Quantum structure based infrared detector research and development within Acreo's centre of excellence IMAGIC2010In: Infrared physics & technology, ISSN 1350-4495, Vol. 53, no 4, 227-230 p.Article in journal (Refereed)
    Abstract [en]

    Acreo has a long tradition of working with quantum structure based infrared (IR) detectors and arrays. This includes QWIP (quantum well infrared photodetector), QDIP (quantum dot infrared photodetector), and InAs/GaInSb based photon detectors of different structure and composition. It also covers R&D on uncooled microbolometers. The integrated thermistor material of such detectors is advantageously based on quantum structures that are optimised for high temperature coefficient and low noise. Especially the SiGe material system is preferred due to the compatibility with silicon technology. The R&D work on IR detectors is a prominent part of Acreo's centre of excellence "IMAGIC" on imaging detectors and systems for non-visible wavelengths. IMAGIC is a collaboration between Acreo, several industry partners and universities like the Royal Institute of Technology (KTH) and Linkoping University. (C) 2010 Elsevier B.V. All rights reserved.

  • 34.
    Andersson, Ulf
    et al.
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC. KTH, School of Computer Science and Communication (CSC).
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Zhang, Ziyang
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Parallel Power Computation for Photonic Crystal Devices2006In: Methods and Applications of Analysis, ISSN 1073-2772, E-ISSN 1945-0001, Vol. 13, no 2, 149-156 p.Article in journal (Refereed)
    Abstract [en]

    Three-dimensional finite-different time-domain (3D FDTD) simulation of photonic crystal devices often demands large amount of computational resources. In many cases it is unlikely to carry out the task on a serial computer. We have therefore parallelized a 3D FDTD code using MPI. Initially we used a one-dimensional topology so that the computational domain was divided into slices perpendicular to the direction of the power flow. Even though the speed-up of this implementation left considerable room for improvement, we were nevertheless able to solve largescale and long-running problems. Two such cases were studied: the power transmission in a two-dimensional photonic crystal waveguide in a multilayered structure, and the power coupling from a wire waveguide to a photonic crystal slab. In the first case, a power dip due to TE/TM modes conversion is observed and in the second case, the structure is optimized to improve the coupling. We have also recently completed a full three-dimensional topology parallelization of the FDTD code.

  • 35.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Modeling of spacer influence on post-dryout heat transfer in heated channels2006In: International Conference on Nuclear Engineering, Proceedings, ICONE Volume 2006, 2006, 7p, 2006Conference paper (Refereed)
    Abstract [en]

    Post-dryout heat transfer plays an important role in safe and economical operations of Light Water Reactors (LWR). This type of heat transfer is avoided under normal operational conditions of nuclear reactors; however, it may occur in transient or accidential situations. To estimate the risk of clad damages due to increase of temperature associated with the occurrence of post-dryout, it is necessary to properly model heat transfer processes under such conditions. The influence of various parameters on heat transfer downstream of spacer has been investigated. It is concluded that heat transfer enhancement due to spacers is largely under-predicted for flows with relatively low quality. For such flows the effect of droplets impinging heated walls is significant and must properly be taken into account. The phenomenological model presented in this paper shows a superior accuracy over correlations and presents a potential to capture the phenomenon of rewetting that occurs downstream of spacers.

  • 36.
    Angulo Barrios, C.
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT. KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Messmer, L. R.
    Holmgren, M.
    Lovqvist, A.
    Carlsson, C.
    Larsson, A.
    Halonen, J.
    Ghisoni, M.
    Stevens, Renaud
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    GaAs/AlGaAs buried-heterostructure laser diodes with semi-insulating GaInP:Fe regrowth2001In: Lasers and Electro-Optics, 2001. CLEO/Pacific Rim 2001. The 4th Pacific Rim Conference on, 2001, Vol. 2Conference paper (Refereed)
    Abstract [en]

    GaAs/AlGaAs buried-heterostructure in-plane lasers and vertical-cavity surface-emitting lasers using GaInP:Fe as the burying layer have been fabricated and investigated. Regrowth of GaInP:Fe around etched laser mesas was achieved by hydride vapor phase epitaxy. The lasers exhibit good performance under CW operation and show promising high-speed characteristics.

  • 37.
    Ao, Xianyu
    et al.
    KTH.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Two-stage design method for realization of photonic bandgap structures with desired symmetries by interference lithography2004In: Optics Express, ISSN 1094-4087, Vol. 12, no 6, 978-983 p.Article in journal (Refereed)
    Abstract [en]

    Interference lithography for the fabrication of photonic crystals is considered. A two-stage design method for realization of photonic bandgap structures with desired symmetries is developed. An optimal photonic crystal with a large bandgap is searched by adjusting some parameters while keeping some basic symmetry of the unit cell unchanged. A nonlinear programming method is then used to find the optimal electric field vectors of the laser beams and realize the desired interference pattern. The present method is useful for a rational and systematical design of new photonic bandgap structures.

  • 38. Arvidsson, G.
    et al.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Anordning i form av koherent ljuskälla baserad på frekvenskonvertering av ljuset från lasrar: [Controllable laser light source uses two laser sources to enable frequency mixing such that three or four new wavelengths may be generated]1990Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The present invention concerns a coherent light source based on frequency conversion of the radiation from two lasers (20, 21) by frequency mixing in optical waveguides (10; 90), which are provided in a substrate (1). The wavelengths for the two lasers (20, 21) should be such, that the phase matching condition for the optically nonlinear frequency conversion is fulfilled in the waveguide structure (10; 90). The frequency conversion is accomplished in the form of frequency mixing, frequency doubling or down conversion in frequency by parametric oscillation so that in total three or four new wavelengths can be generated. By using integrated optics technique the output radiation can be controlled in various ways, for example be switched to different output waveguides, varied in intensity or colour balance.

  • 39. Arvidsson, G.
    et al.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Webjörn, J.
    Vågledare samt förfarande för framställning av sådan: [Quasi-phase-matched optical waveguides and method of making same]1988Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A waveguide (and a method for fabrication of a waveguide) for electromagnetic waves, arranged in an optically non-linear crystal substrate (1), such as LiNbO3, LiTaO3 or KTiOPO4, whereby a periodically domain-inverted structure, with periodically reversed ferroelectric polarity, is provided in a channel waveguide (6), having a higher refractive index than other parts of the substrate. The regions of reversed ferroelectric polarity are achieved by means of a heat treatment yielding a domain-inversion governed by a periodic perturbation in the crystal surface, obtained by use of a periodic mask structure on the crystal surface. The periodic structure is arranged in such a way that it constitutes a quasi-phase-matching structure. Thereby the waveguide is capable of converting light or radiation of a certain wavelength (certain wavelengths) to light or radiation of another predetermined wavelength (other predetermined wavelengths) with high efficiency.

  • 40. Assanto, Gaetano
    et al.
    Gallo, Katia
    Optoelectronics Reserach Centre, University of Southampton.
    Spatial simultons in two-dimensional purely nonlinear lattices2008Conference paper (Refereed)
  • 41. Assanto, Gaetano
    et al.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Pasquazi, Alessia
    Stivala, Salvatore
    Spatial Solitons in 2D Lattices of a Nonlinear Nature2008In: Optics and photonics news (Print), ISSN 1047-6938, E-ISSN 1541-3721, Vol. 19, no 6, 29-32 p.Article in journal (Refereed)
    Abstract [en]

    Researchers have observed two-color optical solitons in a 2D parametric photonic lattices (PPLs) with hexagonal symmetry in lithium niobate. PPLs behave as uniform and homogenous dielectrics under weak excitation whereas, at high powers, they allow for the simultaneous quasi-phase-matching of several susceptibility processes. It has been observed that 2D PPLs support novel simulation space dynamics through twin-beam second-harmonic generation. In the symmetric configuration, solitons can form in an enhanced spectral range for confinement, while in the asymmetric cases, they can be steered by varying the input power and wave-length. Quadratic spatial solitons in planar nonlinear lattices unveils new opportunities for physics and also enable applications of self-trapped light beams, including the engineering of solitons states for analog signal processing and all-optical switching/routing in aperiodic lattices and quasi-crystals.

  • 42. Attwood, D T
    et al.
    Hertz, Hans
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Midorikawa, K
    Obara, M
    Introduction to the issue on short wavelength and EUV lasers2004In: IEEE Journal of Selected Topics in Quantum Electronics, ISSN 1077-260X, E-ISSN 1558-4542, Vol. 10, no 6, 1241-1243 p.Article in journal (Other academic)
  • 43. Audren, A.
    et al.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Possnert, G.
    Damage recovery in ZnO by post-implantation annealing2010In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, Vol. 268, no 11-12, 1842-1846 p.Article in journal (Other academic)
    Abstract [en]

    ZnO bulk samples were implanted with 200 key-Co ions at room temperature with two fluences, 1 x 10(16) and 8 x 10(16) cm(-2), and then annealed in air for 30 min at different temperatures up to 900 degrees C. After the implantation and each annealing step, the samples were analyzed by Rutherford backscattering spectrometry (RBS) in random and channeling directions to follow the evolution of the disorder profile. The RBS spectra reveal that disorder is created during implantation in proportion to the Co fluence. The thermal treatments induce a disorder recovery, which is however, not complete after annealing at 900 degrees C, where about 15% of the damage remains. To study the Co profile evolution during annealing, the samples were, in addition to RBS, characterized by secondary ion mass spectrometry (SIMS). The results show that Co diffusion starts at 800 degrees C, but also that a very different behavior is seen for Co concentrations below and above the solubility limit. (C) 2010 Elsevier B.V. All rights reserved.

  • 44.
    Avramidis, Stefanos
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Simulation and parameter estimation of spectrophotometric instruments 2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The paper and the graphics industries use two instruments with different optical geometry (d/0 and 45/0) to measure the quality of paper prints. The instruments have been reported to yield incompatible measurements and even rank samples differently in some cases, causing communication problems between these sectors of industry.A preliminary investigation concluded that the inter-instrument difference could be significantly influenced by external factors (background, calibration, heterogeneity of the medium). A simple methodology for eliminating these external factors and thereby minimizing the instrument differences has been derived. The measurements showed that, when the external factors are eliminated, and there is no fluorescence or gloss influence, the inter-instrument difference becomes small, depends on the instrument geometry, and varies systematically with the scattering, absorption, and transmittance properties of the sample.A detailed description of the impact of the geometry on the results has been presented regarding a large sample range. Simulations with the radiative transfer model DORT2002 showed that the instruments measurements follow the physical radiative transfer model except in cases of samples with extreme properties. The conclusion is that the physical explanation of the geometrical inter-instrument differences is based on the different degree of light permeation from the two geometries, which eventually results in a different degree of influence from near-surface bulk scattering. It was also shown that the d/0 instrument fulfils the assumptions of a diffuse field of reflected light from the medium only for samples that resemble the perfect diffuser but it yields an anisotropic field of reflected light when there is significant absorption or transmittance. In the latter case, the 45/0 proves to be less anisotropic than the d/0.In the process, the computational performance of the DORT2002 has been significantly improved. After the modification of the DORT2002 in order to include the 45/0 geometry, the Gauss-Newton optimization algorithm for the solution of the inverse problem was qualified as the most appropriate one, after testing different optimization methods for performance, stability and accuracy. Finally, a new homotopic initial-value algorithm for routine tasks (spectral calculations) was introduced, which resulted in a further three-fold speedup of the whole algorithm.The paper and the graphics industries use two instruments with different optical geometry (d/0 and 45/0) to measure the quality of paper prints. The instruments have been reported to yield incompatible measurements and even rank samples differently in some cases, causing communication problems between these sectors of industry.A preliminary investigation concluded that the inter-instrument difference could be significantly influenced by external factors (background, calibration, heterogeneity of the medium). A simple methodology for eliminating these external factors and thereby minimizing the instrument differences has been derived. The measurements showed that, when the external factors are eliminated, and there is no fluorescence or gloss influence, the inter-instrument difference becomes small, depends on the instrument geometry, and varies systematically with the scattering, absorption, and transmittance properties of the sample.A detailed description of the impact of the geometry on the results has been presented regarding a large sample range. Simulations with the radiative transfer model DORT2002 showed that the instruments measurements follow the physical radiative transfer model except in cases of samples with extreme properties. The conclusion is that the physical explanation of the geometrical inter-instrument differences is based on the different degree of light permeation from the two geometries, which eventually results in a different degree of influence from near-surface bulk scattering. It was also shown that the d/0 instrument fulfils the assumptions of a diffuse field of reflected light from the medium only for samples that resemble the perfect diffuser but it yields an anisotropic field of reflected light when there is significant absorption or transmittance. In the latter case, the 45/0 proves to be less anisotropic than the d/0.In the process, the computational performance of the DORT2002 has been significantly improved. After the modification of the DORT2002 in order to include the 45/0 geometry, the Gauss-Newton optimization algorithm for the solution of the inverse problem was qualified as the most appropriate one, after testing different optimization methods for performance, stability and accuracy. Finally, a new homotopic initial-value algorithm for routine tasks (spectral calculations) was introduced, which resulted in a further three-fold speedup of the whole algorithm.

  • 45. Bach, Florian
    et al.
    Mero, Mark
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Physics.
    Zukauskas, Andrius
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Petrov, Valentin
    High repetition rate, femtosecond and picosecond laser induced damage thresholds of Rb:KTiOPO4 at 1.03 mu m2017In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, no 3, 744-750 p.Article in journal (Refereed)
    Abstract [en]

    A laser-induced damage study is performed on blank, uncoated Rb:KTiOPO4 (RKTP) samples at 1.03 mu m with two different pulse durations of similar to 0.3 and similar to 1.0 ps and a repetition rate of 100 kHz. The effect of the sample temperature is also considered.

  • 46. Baek, I. H.
    et al.
    Choi, S. Y.
    Lee, H. W.
    Cho, W. B.
    Petrov, V.
    Agnesi, A.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Yeom, D. -I
    Kim, K.
    Hong, B. H.
    Rotermund, F.
    Passive mode-locking of a Ti: Sapphire laser using low-dimensional carbon nanostructures2011In: Int. Quantum Electron. Conf., IQEC Conf. Lasers Electro-Opt., CLEO Pac. Rim. Incorporating Australas. Conf. Opt., Lasers Spec, 2011, 1154-1155 p.Conference paper (Refereed)
    Abstract [en]

    We report on passive mode-locking of a Ti:sapphire laser employing novel saturable absorbers based on low-dimensional carbon nanostructures such as single-walled carbon nanotubes and monolayer graphene. The mode-locked operation with both saturable absorbers were characterized and compared to pure Kerr-lens mode-locking.

  • 47. Baek, In Hyung
    et al.
    Choi, Sun Young
    Lee, Hwang Woon
    Cho, Won Bae
    Petrov, Valentin
    Agnesi, Antonio
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Yeom, Dong-Il
    Kim, Kihong
    Rotermund, Fabian
    Single-walled carbon nanotube saturable absorber assisted high-power mode-locking of a Ti:sapphire laser2011In: Optics Express, ISSN 1094-4087, Vol. 19, no 8, 7833-7838 p.Article in journal (Refereed)
    Abstract [en]

    We report on passive mode-locking of a Ti:sapphire laser employing a single-walled carbon nanotube saturable absorber (SWCNT-SA) specially designed and fabricated for wavelengths near 800 nm. Mode-locked pulses as short as 62 fs were generated at a repetition rate of 99.4 MHz. We achieved output powers from the SWCNT-SA mode-locked laser as high as 600 mW with a slope efficiency of 26%. The characteristics of SWCNT-SA-assisted mode-locking were compared with those of Kerr-lens mode-locking without SWCNT-SA.

  • 48. Baev, A
    et al.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Gelmukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    de Brito, N
    Bjorneholm, O
    Svensson, S
    Picturing molecular femtosecond processes through an ultra-fast controllable X-ray shutter2003In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 289, no 1, 51-56 p.Article in journal (Refereed)
    Abstract [en]

    We show that frequency detuning in a resonant X-ray scattering experiment acts as an X-ray camera shutter by regulating the duration time of the scattering process. The camera shutter can be used to select processes at different time scales for observation. This is illustrated by a resonant Auger study of the ultra-fast dissociation of the core-excited HF molecule. We present experimental results and first principle simulations of the molecular fraction in the resonant Auger spectra of HF which is a dynamical parameter that well illustrates X-ray shutter controlled dissociation.

  • 49. Baev, Alexander
    et al.
    Prasad, Paras N.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Samoc, Marek
    Wegener, Martin
    Metaphotonics: An emerging field with opportunities and challenges2015In: Physics reports, ISSN 0370-1573, E-ISSN 1873-6270, Vol. 594, 1-60 p.Article, review/survey (Refereed)
    Abstract [en]

    Metaphotonics is an emerging multidisciplinary field that deals with manipulation of electro-magnetic fields in nanoengineered (meta)materials using both electric and magnetic interactions and their cross-coupling. It offers unprecedented control of both linear and nonlinear optical functions for applications ranging from optical switching, to negative- and near-zero refractive index metamaterials, to chiral bioimaging, to cloaking. However, realization of such applications requires physics-guided nanoengineering of appropriate artificial media with electro-magnetic properties at visible and infrared wavelengths that are tailored to surpass those of any naturally-occurring material. Here, we review metaphotonics with a broadened vision and scope, introduce potential applications, describe the role of theoretical physics through multiscale modeling, review the materials development and current status, and outline opportunities in this fertile emerging field.

  • 50.
    Baghban, Mohammad Amin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Second-Harmonic Generation Engineering in Lithium Niobate Nanopillars2015Conference paper (Refereed)
1234567 1 - 50 of 1290
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