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  • 201. Collin, A
    et al.
    Lundh, Emil
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Suominen, K A
    Center-of-mass rotation and vortices in an attractive Bose gas2005Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 71, nr 2, s. 023613-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rotational properties of an attractively interacting Bose gas are studied using analytical and numerical methods. We study perturbatively the ground-state phase space for weak interactions, and find that in an anharmonic trap the rotational ground states are vortex or center-of-mass rotational states; the crossover line separating these two phases is calculated. We further show that the Gross-Pitaevskii equation is a valid description of such a gas in the rotating frame and calculate numerically the phase-space structure using this equation. It is found that the transition between vortex and center-of-mass rotation is gradual; furthermore, the perturbative approach is valid only in an exceedingly small portion of phase space. We also present an intuitive picture of the physics involved in terms of correlated successive measurements for the center-of-mass state.

  • 202. Coucheron, David A.
    et al.
    Fokine, Michael
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Patil, Nilesh
    Breiby, Dag Werner
    Buset, Ole Tore
    Healy, Noel
    Peacock, Anna C.
    Hawkins, Thomas
    Jones, Max
    Ballato, John
    Gibson, Ursula J.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres2016Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, artikel-id 13265Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core.

  • 203.
    Couto, Rafael C.
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Univ Fed Goias, Brazil.
    Guarise, Marco
    Nicolaou, Alessandro
    Jaouen, Nicolas
    Chiuzbaian, Gheorghe S.
    Luening, Jan
    Ekholm, Victor
    Rubensson, Jan-Erik
    Sathe, Conny
    Hennies, Franz
    Kimberg, Victor
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Guimaraes, Freddy F.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Gel'mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Journel, Loic
    Simon, Marc
    Anomalously strong two-electron one-photon X-ray decay transitions in CO caused by avoided crossing2016Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, artikel-id 20947Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The unique opportunity to study and control electron-nuclear quantum dynamics in coupled potentials offered by the resonant inelastic X-ray scattering (RIXS) technique is utilized to unravel an anomalously strong two-electron one-photon transition from core-excited to Rydberg final states in the CO molecule. High-resolution RIXS measurements of CO in the energy region of 12-14 eV are presented and analyzed by means of quantum simulations using the wave packet propagation formalism and ab initio calculations of potential energy curves and transition dipole moments. The very good overall agreement between the experimental results and the theoretical predictions allows an in-depth interpretation of the salient spectral features in terms of Coulomb mixing of "dark" with "bright" final states leading to an effective two-electron one-photon transition. The present work illustrates that the improved spectral resolution of RIXS spectra achievable today may call for more advanced theories than what has been used in the past.

  • 204. Cui, Yanxia
    et al.
    Fung, Kin Hung
    Xu, Jun
    Yi, Jin
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Fang, Nicholas X.
    Exciting multiple plasmonic resonances by a double-layered metallic nanostructure2011Ingår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 28, nr 11, s. 2827-2832Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By placing a metallic layer of a periodic nanostrip array above a metallic layer of a periodic nanogroove array with a separation of 120nm, we obtain a triple-band thin film absorber with all its resonant wavelengths displaying absorptivity greater than 90%. Through a systematic study of the current compound structure, we find these three absorption peaks mainly depend on some simple resonances, i.e., the modes supported by the nanostrip array in the top layer, the nanogroove array in the bottom layer, and the horizontal cavity between the two layers. In addition, we show that this kind of absorber is quite robust and fairly insusceptible to the parallel shift between the two different layers. This study should contribute to the design of thin film absorbers/ emitters.

  • 205. Céolin, Denis
    et al.
    Liu, Ji-Cai
    Vaz da Cruz, Vinicius
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi. KTH.
    Ågren, Hans
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Journel, Loïc
    Guillemin, Renaud
    Marchenko, Tatiana
    Kushawaha, Rajesh K.
    Piancastelli, Maria-Novella
    Püttner, Ralph
    Simon, Marc
    Gel'mukhanov, Faris
    Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effectManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Observing and controlling molecular motion, and in particular rotation,is a fundamental topic in physics and chemistry. In order toinitiate ultrafast rotation, one needs a way to transfer a large angularmomentum to the molecule. As a showcase, this was performedby hard x-ray C1s ionization of carbon monoxide, accompanied byspinning-up the molecule via the recoil “kick” of the emitted fast photoelectron.To visualize this molecular motion, we use the dynamicalrotational Doppler effect and an X-ray “pump-probe” device offeredby nature itself: the recoil-induced ultrafast rotation is probed by subsequentAuger electron emission. The time information in our experimentorigins from the natural delay between the C1s photoionizationinitiating the rotation and the ejection of the Auger electron. From amore general point of view, time-resolved measurements can be performedin two ways: either to vary the "delay" time as in conventionaltime-resolved pump-probe spectroscopy and to use the dynamicsgiven by the system, or to keep constant "delay" time and to manipulatethe dynamics. Since in our experiment we cannot change the delaytime given by the core-hole lifetime $\tau$, we use the second optionand control the rotational speed by changing the kinetic energy of thephotoelectron. The recoil-induced rotational dynamics controlled insuch a way is observed as a photon-energy dependent asymmetryof the Auger lineshape, in full agreement with theory. This asymmetryis explained by a significant change of the molecular orientationduring the core-hole lifetime, which is comparable with the rotationalperiod.

  • 206.
    Daemi, Bita
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    How to measure the Transverse Chromatic Aberration of the human eye in off-axis angels2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Peripheral vision plays an important role for visually impaired people with central field loss. Furthermore, recent studies show that defocus in the image on the peripheral retina might influence the development of myopia. Apart from the refractive errors and astigmatism, off-axis aberrations such as coma and transverse chromatic aberration (TCA) also influence the image quality on the peripheral retina. Theory shows that the amount of TCA is quite large in peripheral vision especially in large off-axis angles. The aim of this study is to develop a method to measure the amount of TCA in the peripheral field of view of the human eye.

    The method which was used for this study was subjective and the amount of TCA was measured in the left eye of the three volunteer adult subjects. The method was based on measuring the TCA as a chromatic difference of position outside of the eye. The measurements were done in the nasal retina of the eye in seven angles from 0 deg eccentricity (fovea) to 60 deg eccentricity. To compare the experimental results with theoretical values two schematic eye models were implemented in ZEMAX optical design software; a reduced eye model and a wide angle eye model.

    The results showed the expected increase of TCA with off-axis angle. The measurements for two subjects were in good agreement with the eye models. The magnitudes for TCA varied between subjects, one reason for this can be related to the different shapes of the eye in different subjects. The third subject had different values for TCA. This difference led us to investigate the reliability and the repeatability of the method in more detail.

  • 207.
    Daemi, Bita
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Advanced image analysis verifies geometry performance of micro-milling systems2017Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 56, nr 10, s. 2912-2921Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Accurate dimensional measurement of micro-milled items is a challenge and machine specifications do not include operational parameters in the workshop. Therefore, a verification test that shows the machine's overall geometrical performance over its working area would help machine users in the assessment and adjustment of their equipment. In this study, we present an optical technique capable of finding micro-milled features at submicron uncertainty over working areas > 10 cm(2). The technique relies on an ultra-precision measurement microscope combined with advanced image analysis to get the center of gravity of milled cross-shaped features at subpixel levels. Special algorithms had to be developed to handle the disturbing influence of burr and milling marks. The results show repeatability, reproducibility, and axis straightness for three micro-milling facilities and also discovered an unknown 2 mu m amplitude undulation in one of them.

  • 208.
    Dahlberg, Carl F. O.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Mitchell-Thomas, R. C.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Reducing the Dispersion of Periodic Structures with Twist and Polar Glide Symmetries2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikel-id 10136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, a number of guiding structures are proposed which take advantage of higher symmetries to vastly reduce the dispersion. These higher symmetries are obtained by executing additional geometrical operations to introduce more than one period into the unit cell of a periodic structure. The specific symmetry operations employed here are a combination of p-fold twist and polar glide. Our dispersion analysis shows that a mode in a structure possessing higher symmetries is less dispersive than in a conventional structure. It is also demonstrated that, similar to the previously studied Cartesian glide-symmetric structures, polar glide-symmetric structures also exhibit a frequency independent response. Promising applications of these structures are leaky-wave antennas which utilize the low frequency dependence.

  • 209.
    Dahlgren, Hanna
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Multi-spectral analysis of fine scale aurora2010Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The Aurora Borealis is the visible manifestation of the complex plasma interaction between the solar wind and the Earth's magnetosphere and ionosphere. Ground based and in situ measurements demonstrate a prevalence of dynamic fine structure within auroral displays, with spatial scales down to tens of metres and time variations occurring on a fraction of a second.The fine-scale morphology is related to structuring of auroral currents and electric fields and detailed spatial, spectral and temporal observations of the aurora are crucial in understanding the electrodynamic processes taking place in the ionosphere and in its coupling to the magnetosphere.

    In this thesis, the low-light optical instrument ASK (Auroral Structure and Kinetics) is used to image small-scale structures in the aurora at very high spatial and temporal resolution. ASK is a multi-spectral instrument, imaging the aurora in three selected emissions simultaneously. This provides information on the energy of the precipitating electrons. The SIF (Spectrographic Imaging Facility) instrument has been used in conjunction with ASK, to give a more complete picture of the spectral characteristics of the aurora, and to determine the degree of contaminating emissions present in the same spectral interval as the emission lines observed by ASK.

    Data from ASK and SIF are used to study the relation between the morphology and dynamics of small-scale structures in the aurora and the energy of the precipitating electrons. By comparing electron density profiles provided by EISCAT (European Incoherent SCATter) radar measurements with modeling results, information on the characteristic energy and the energy flux of the precipitating electrons can be obtained. One of the ASK channels is imaging a metastable O+ emission, which has a lifetime of about 5 s. By tracing the afterglow in this channel optically a direct measure of the E x B drift is obtained from which the local ionospheric electric field can be calculated. ASK data has also been used to analyse the properties of a distorted auroral arc, in which auroral structuring was found to take place simultaneously at different spatial scales. The smallest features, 'ruffs', are undulations found to develop on the edge of an auroral curl, fold or shear. Detailed optical studies of black aurora, including both the type which is associated with plasma shear motions and no or weak shear motions were conducted from ASK data, to investigate the spectral properties and fine scale morphology of the black structures and to shed light on the processes behind this phenomenon.

  • 210.
    Dai, Daoxin
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    He, S L
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Calculation of the spectral response of an arrayed-waveguide gating demultiplexer with a wide-angle beam propagation method in a cylindrical coordinate system2004Ingår i: Optical and quantum electronics, ISSN 0306-8919, E-ISSN 1572-817X, Vol. 36, nr 11, s. 967-979Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The spectral response of an arrayed-waveguide grating (AWG) demultiplexer is calculated by simulating the field propagation in the output section of an AWG with a wide-angle beam propagation method (BPM) in a cylindrical coordinate system. As in a practical design of an AWG demultiplexer, each output waveguide consists of two straight sections connected by a bending section. The spectral response obtained by the present algorithm is more accurate than those obtained with two popular approximate methods, namely, the conventional overlapped integral method and the standard BPM for radially straight and infinitely long output waveguides. With the present algorithm, the dependence of the spectral response on the parameters of the output section is analyzed. The channel crosstalk and the 3 dB passband width of the spectral response depend mainly on the length of the first straight section, the end separation and the angular separation of the output waveguides. The bending section results in an asymmetrical spectral response with remarkable sidelobes which can be reduced by increasing the bending radius.

  • 211.
    Dai, Jin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO.
    Near-Field Radiative Heat Transfer between Plasmonic Nanostructures2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Radiative heat transfer (RHT) due to coupled electromagnetic near field scan significantly exceed that dictated by Planck’s law. Understanding such phenomenon is not only of fundamental scientific interest, but also relevant to a broad range of applications especially connected to nanotechnologies.This dissertation elaborates, through a scattering approach based on the rigorous coupled wave analysis method, how plasmonic nanostructures can tame the near-field RHT between two bodies. The transmission-factor spectra are corroborated by photonic band diagrams computed using a finite element method. The main work begins by showing that the phenomenon of spoofsurface plasmon polariton (SSPP) guided on grooved metal surfaces can play a similar role as surface phonon polariton in enhancing the RHT between two closely placed plates. Since dispersions of SSPPs especially their resonance frequencies can be engineered through geometrical surface profiling,one has great freedom in tailoring spectral properties of near-field RHT. Further enhancement of RHT can be achieved through techniques like filling of dielectrics in grooves or deploying supercells. A thorough study of RHT betweentwo 1D or 2D grooved metal plates confirms super-Planckian RHT at near-field limit, with 2D grooved metal plates exhibiting a superior frequency selectivity. We also present RHT with a more exotic type of plasmonic nanostructures consisting of profile-patterned hyperbolic metamaterial arrays, and show that with such plasmonic nanostructures one can achieve an ultrabroadband super-Planckian RHT.

  • 212.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jaksic, Zoran
    Exact analytical solution for fields in a lossy cylindrical structure with hyperbolic tangent gradient index metamaterials2016Ingår i: Optical and quantum electronics, ISSN 0306-8919, E-ISSN 1572-817X, Vol. 48, nr 3, artikel-id 209Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The advent of metamaterials with tailorable frequency dispersion ensured the emergence of transformation optics with proposed applications that include cloaking devices, superconcentrators, superabsorbers, beam shapers and benders, field and polarization rotators, etc. A crucial property of interest for transformation optics is the possibility to custom design the spatial dependence of optical properties, i.e. to attain a gradient of effective refractive index. The cylindrical geometry has been one of the prototypal proposed forms and actually the first theoretical and experimental cloaking devices had radial symmetry. In this contribution we present an exact analytical approach to the solution of Helmholtz' equations applied to radial propagation of electromagnetic waves through a cylinder containing negative and positive refractive index parts. A hyperbolic tangent gradient of refractive index is assumed. Our approach is inspired by the correspondence between transformation optics and quantum mechanics. A remarkably simple exact analytical solution is derived that takes into account realistic losses in negative-positive refractive index material composites.

  • 213.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Doncov, N.
    Univ Nis, Nish, Serbia.
    Jaksic, Z.
    Univ Belgrade, Belgrade, Serbia.
    Lossy gradient index transmission optics with arbitrary periodic permittivity and permeability and constant impedance throughout the structure2012Ingår i: Journal of Optics, ISSN 2040-8978, E-ISSN 2040-8986, Vol. 14, nr 6, s. 065102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A remarkably simple exact analytical solution is obtained for the electromagnetic field distribution across infinite metamaterial-containing composites with any arbitrary periodic variation of complex effective permittivity and permeability for the case of constant impedance across the structure. Arbitrary temporal dispersion and losses are allowed and the model is generally applicable to different inhomogeneous and anisotropic media simultaneously containing positive and negative refractive index constituents, as long as the effective medium approximation remains valid. The analytical solution is validated by a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms, where a close agreement between the analytic and numerical results is obtained.

  • 214. Daniel, Salman
    et al.
    Saastamoinen, Kimmo
    Saastamoinen, Toni
    Rahomaki, Jussi
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Friberg, Ari T.
    Visser, Taco D.
    Dynamic control of optical transmission through a nano-slit using surface plasmons2015Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, nr 17, s. 22512-22519Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate how the optical transmission by a directly illuminated, sub-wavelength slit in a metal film can be dynamically controlled by varying the incident beam's phase relative to that of a stream of surface plasmon polaritions which are generated at a nearby grating. The transmission can be smoothly altered from its maximum value to practically zero. The results from a simple model and from rigorous numerical simulations are in excellent agreement with our experimental results. Our method may be applied in all-optical switching.

  • 215. Daurer, Benedikt J.
    et al.
    Okamoto, Kenta
    Bielecki, Johan
    Maia, Filipe R. N. C.
    Muhlig, Kerstin
    Seibert, M. Marvin
    Hantke, Max F.
    Nettelblad, Carl
    Benner, W. Henry
    Svenda, Martin
    Timneanu, Nicusor
    Ekeberg, Tomas
    Loh, N. Duane
    Pietrini, Alberto
    Zani, Alessandro
    Rath, Asawari D.
    Westphal, Daniel
    Kirian, Richard A.
    Awel, Salah
    Wiedorn, Max O.
    van der Schot, Gijs
    Carlsson, Gunilla H.
    Hasse, Dirk
    Sellberg, Jonas A.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Barty, Anton
    Andreasson, Jakob
    Boutet, Sebastian
    Williams, Garth
    Koglin, Jason
    Andersson, Inger
    Hajdu, Janos
    Larsson, Daniel S. D.
    Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses2017Ingår i: IUCrJ, ISSN 0972-6918, E-ISSN 2052-2525, Vol. 4, s. 251-262Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of similar to 40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from similar to 35 to similar to 300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 * 10(12) photons per mu m(2) per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.

  • 216.
    Davison, Richard A.
    et al.
    Harvard Univ, Dept Phys, Cambridge, MA 02138 USA.;Univ Cambridge, Dept Appl Math & Theoret Phys, Cambridge CB3 0WA, England..
    Gentle, Simon A.
    Univ Utrecht, Inst Theoret Phys, NL-3508 TD Utrecht, Netherlands.;Leiden Univ, Inst Lorentz Theoret Phys, NL-2333 CA Leiden, Netherlands..
    Goutéraux, Blaise
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Slow Relaxation and Diffusion in Holographic Quantum Critical Phases2019Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, nr 14, artikel-id 141601Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dissipative dynamics of strongly interacting systems are often characterized by the timescale set by the inverse temperature tau(p) similar to h/(k(B)T). We show that near a class of strongly interacting quantum critical points that arise in the infrared limit of translationally invariant holographic theories, there is a collective excitation (a quasinormal mode of the dual black hole spacetime) whose lifetime tau(eq) is parametrically longer than tau(p): tau(eq) >> T-1. The lifetime is enhanced due to its dependence on a dangerously irrelevant coupling that breaks the particle-hole symmetry and the invariance under Lorentz boosts of the quantum critical point. The thermal diffusivity (in units of the butterfly velocity) is anomalously large near the quantum critical point and is governed by tau(eq) rather than tau(p). We conjecture that there exists a long-lived, propagating collective mode with velocity v(s), and in this case the relation D = v(s)(2)tau(eq) holds exactly in the limit T tau(eq) >> 1. While scale invariance is broken, a generalized scaling theory still holds provided that the dependence of observables on the dangerously irrelevant coupling is incorporated. Our work further underlines the connection between dangerously irrelevant deformations and slow equilibration.

  • 217. De Angelis, M.
    et al.
    De Nicola, S.
    Finizio, A.
    Pierattini, G.
    Ferraro, P.
    Grilli, Simonetta
    Paturzo, M.
    Evaluation of the internal field in lithium niobate ferroelectric domains by an interferometric method2004Ingår i: Applied physics letters, ISSN 0003-6951, Vol. 85, nr 4, s. 2785-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the evaluation of internal electric field of a ferroelectric engineered-domain in a LiNbO3 wafer crystal by detecting optical path length variation with a noninvasive interferometric inspection method. The lithium niobate wafer has been patterned and subjected to electric field poling to obtain two antiparallel ferroelectric domains separated by a single domain wall. The crystal has been mounted into one arm of a Mach-Zehnder-type interferometer to study the phase map and evaluate the effects of domain reversion by a digital holographic technique. Evaluation of the internal field and consequent variation of the electro-optical properties of the different domains is analyzed.

  • 218. de la Hoz, P.
    et al.
    Björk, Gunnar G.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Klimov, A. B.
    Leuchs, G.
    Sanchez-Soto, L. L.
    Unpolarized states and hidden polarization2014Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, nr 4, s. 043826-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We capitalize on a multipolar expansion of the polarization density matrix, in which multipoles appear as successive moments of the Stokes variables. When all the multipoles up to a given order K vanish, we can properly say that the state is Kth-order unpolarized, as it lacks of polarization information to that order. First-order unpolarized states coincide with the corresponding classical ones, whereas unpolarized to any order tally with the quantum notion of fully invariant states. In between these two extreme cases, there is a rich variety of situations that are explored here. The existence of hidden polarization emerges in a natural way in this context.

  • 219.
    De Luca, Eleonora
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Visser, Dennis
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Anand, Srinivasan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Swillo, Marcin
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Gallium indium phosphide nanostructures with suppressed photoluminescence for applications in nonlinear optics2018Ingår i: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Nanostructured GaInP shows remarkable second-order nonlinear properties. By measuring the second harmonic generation before and after stimulating intrinsic photobleaching, we observed suppressed photoluminescence and unchanged nonlinear properties, making it suitable for low-noise applications. 

  • 220. de Oliveira, R.
    et al.
    Sjödin, N.
    Fokine, Michael
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Margulis, Walter
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    de Matos, C.
    Norin, L.
    Fabrication and Optical Characterization of Silica Optical Fibers Containing Gold Nanoparticles2015Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, nr 1, s. 370-375Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Gold nanoparticles have been used since antiquity for the production of red-colored glasses. More recently, it was determined that this color is caused by plasmon resonance, which additionally increases the material's nonlinear optical response, allowing for the improvement of numerous optical devices. Interest in silica fibers containing gold nanoparticles has increased recently, aiming at the integration of nonlinear devices with conventional optical fibers. However, fabrication is challenging due to the high temperatures required for silica processing and fibers with gold nanoparticles were solely demonstrated using sol-gel techniques. We show a new fabrication technique based on standard preform/fiber fabrication methods, where nanoparticles are nucleated by heat in a furnace or by laser exposure with unprecedented control over particle size, concentration, and distribution. Plasmon absorption peaks exceeding 800 dB m(-1) at 514-536 nm wavelengths were observed, indicating higher achievable nanoparticle concentrations than previously reported. The measured resonant nonlinear refractive index, (6.75 ± 0.55) × 10(-15) m(2) W(-1), represents an improvement of >50×.

  • 221.
    Degerman Engfeldt, Johnny
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Georen, Peter
    Lagergren, Carina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, N Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Methodology for measuring current distribution effects in electrochromic smart windows2011Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, nr 29, s. 5639-5646Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrochromic (EC) devices for use as smart windows have a large energy-saving potential when used in the construction and transport industries. When upscaling EC devices to window size, a well-known challenge is to design the EC device with a rapid and uniform switching between colored (charged) and bleached (discharged) states. A well-defined current distribution model, validated with experimental data, is a suitable tool for optimizing the electrical system design for rapid and uniform switching. This paper introduces a methodology, based on camera vision, for experimentally validating EC current distribution models. The key is the methodology's capability to both measure and simulate current distribution effects as transmittance distribution. This paper also includes simple models for coloring (charging) and bleaching (discharging), taking into account secondary current distribution with charge transfer resistance and ohmic effects. Some window-size model predictions are included to show the potential for using a validated EC current distribution model as a design tool.

  • 222.
    Degerman Engfeldt, Johnny
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Georen, Peter
    Lagergren, Carina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, N Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Predicting Performance of Large Area Electrochromic Smart WindowsArtikel i tidskrift (Övrigt vetenskapligt)
  • 223. Del Monte, E.
    et al.
    Barbiellini, G.
    Fuschino, F.
    Giuliani, A.
    Longo, F.
    Marisaldi, M.
    Moretti, Elena
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Trifoglio, M.
    Argan, A.
    Bulgarelli, A.
    Caraveo, P.
    Cattaneo, P. W.
    Chen, A.
    Costa, E.
    Di Cocco, G.
    Donnarumma, I.
    Evangelista, Y.
    Feroci, M.
    Galli, M.
    Gianotti, F.
    Labanti, C.
    Lapshov, I.
    Lazzarotto, F.
    Lipari, P.
    Mereghetti, S.
    Morselli, A.
    Pacciani, L.
    Pellizzoni, A.
    Perotti, F.
    Picozza, P.
    Pilia, M.
    Prest, M.
    Pucella, G.
    Rapisarda, M.
    Rappoldi, A.
    Soffitta, P.
    Tavani, M.
    Trois, A.
    Vallazza, E.
    Vercellone, S.
    Vittorini, V.
    Pittori, C.
    Salotti, L.
    The observation of GRBs with AGILE and the interesting cases of GRB 090618 and GRB 100724B2011Ingår i: AIP Conf. Proc., 2011, s. 209-212Konferensbidrag (Refereegranskat)
    Abstract [en]

    The AGILE satellite, in orbit since 2007, is localizing about 0.5 GRBs per month with the hard X-ray Imager superagile (18-60 keV) and is detecting around 1 GRB per week with the non-imaging Minicalorimeter (0.35 - 100 MeV). Up to now the AGILE Gamma Ray Imaging Detector firmly detected four GRBs in the energy band between 20 MeV and few GeV. In this presentation we review the status of the GRBs observation with AGILE, we discuss the upper limits in the gamma-ray band of the non-detected events and we show some interesting bursts, especially GRB 090618 (bright in soft and hard-X rays, optical and radio but lacking GeV emission) and GRB 100724B (with a bright GeV emission simultaneous to hard-X rays without delayed onset).

  • 224. Demchenko, P.
    et al.
    Gomon, D.
    Anoshkin, Ilya V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Lioubtchenko, Dmitri
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Khodzitsky, M.
    Study of optical pumping influence on carbon nanotubes permittivity in THz frequency range2018Ingår i: Journal of Physics: Conference Series, Institute of Physics Publishing , 2018, nr 5Konferensbidrag (Refereegranskat)
    Abstract [en]

    Equivalent complex permittivity of carbon nanotubes (CNT) was measured with/without light illumination at the frequency range of 0.2-1 THz. It was shown that we can tune the dispersion of the CNT complex conductivity during varying of optical pumping (wavelength of 980 nm). These results mean that CNT is perspective candidate for development of THz tunable attenuators and phase shifters. 

  • 225. Deng, Lei
    et al.
    Beltrán, Marta
    Pang, Xiaodan
    RISE ACREO AB.
    Zhang, Xu
    Arlunno, Valeria
    Zhao, Ying
    Caballero, Antonio
    Dogadaev, Anton
    Yu, Xianbin
    Llorente, Roberto
    Liu, Deming
    Tafur Monroy, I
    Fiber Wireless Transmission of 8.3-Gb/s/ch QPSK-OFDM Signals in 75–110-GHz Band2012Ingår i: Photonics Technology Letters, IEEE, Vol. 24, nr 5, s. 383-385Artikel i tidskrift (Refereegranskat)
  • 226. Deng, Lei
    et al.
    Liu, Deming
    Pang, Xiaodan
    RISE ACREO AB.
    Zhang, Xu
    Arlunno, Valeria
    Zhao, Ying
    Caballero, Antonio
    Dogadaev, Anton K
    Yu, Xianbin
    Monroy, Idelfonso Tafur
    Beltran, Marta
    Llorente, Roberto
    42.13 Gbit/S 16qam-OFDM Photonics-Wireless Transmission in 75-110 GHz Band2012Ingår i: Progress In Electromagnetics Research, Vol. 126, s. 449-461Artikel i tidskrift (Refereegranskat)
  • 227. Deng, Lei
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Monroy, Idelfonso Tafur
    Tang, Ming
    Shum, Ping
    Liu, Deming
    Experimental demonstration of nonlinearity and phase noise tolerant 16-QAM OFDM W-band (75–110 GHz) signal over fiber system2014Ingår i: Journal of Lightwave Technology, Vol. 32, nr 8, s. 1442-1448Artikel i tidskrift (Refereegranskat)
  • 228. Deng, Lei
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Zhang, Xu
    Yu, Xianbin
    Liu, Deming
    Monroy, Idelfonso Tafur
    Nonlinearity and Phase Noise Tolerant 75-110 GHz Signal over Fiber System Using Phase Modulation Technique2013Ingår i: National Fiber Optic Engineers Conference, 2013Konferensbidrag (Refereegranskat)
  • 229. Deng, Lei
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Zhao, Ying
    Othman, M Binti
    Jensen, Jesper Bevensee
    Zibar, Darko
    Yu, Xianbin
    Liu, Deming
    Monroy, Idelfonso Tafur
    2x2 MIMO-OFDM Gigabit fiber-wireless access system based on polarization division multiplexed WDM-PON2012Ingår i: Optics express, Vol. 20, nr 4, s. 4369-4375Artikel i tidskrift (Refereegranskat)
  • 230. Deng, Lei
    et al.
    Zhao, Ying
    Pang, Xiaodan
    RISE ACREO AB.
    Tang, Ming
    Shum, Ping
    Liu, Deming
    All-VCSEL Transmitters With Remote Optical Injection for WDM-OFDM-PON2014Ingår i: IEEE Photonics Technology Letters, Vol. 26, nr 5, s. 461-464Artikel i tidskrift (Refereegranskat)
  • 231. Deng, Lei
    et al.
    Zhao, Ying
    Pang, Xiaodan
    RISE ACREO AB.
    Yu, Xianbin
    Jensen, J Bevensee
    Liu, Deming
    Monroy, I Tafur
    Colorless ONU based on all-VCSEL sources with remote optical injection for WDM-PON2011Ingår i: Photonics Conference (PHO), 2011 IEEE, 2011, s. 220-221Konferensbidrag (Refereegranskat)
  • 232. Deng, Lei
    et al.
    Zhao, Ying
    Pang, Xiaodan
    RISE ACREO AB.
    Yu, Xianbin
    Liu, Deming
    Monroy, Idelfonso Tafur
    Intra and inter-PON ONU to ONU virtual private networking using OFDMA in a ring topology2011Ingår i: Microwave Photonics, 2011 International Topical Meeting on & Microwave Photonics Conference, 2011 Asia-Pacific, MWP/APMP, 2011, s. 176-179Konferensbidrag (Refereegranskat)
  • 233.
    Deniel, L.
    et al.
    Univ Paris Sud, Univ Paris Saclay, CNRS, Ctr Nanosci & Nanotechnol, F-91120 Palaiseau, France..
    Gay, M.
    Univ Rennes, CNRS, FOTON, UMR 6082, F-22305 Lannion, France..
    Perez Galacho, D.
    Univ Paris Sud, Univ Paris Saclay, CNRS, Ctr Nanosci & Nanotechnol, F-91120 Palaiseau, France.;Univ Politecn Valencia, ITEAM Res Inst, Camino Vera S-N, E-46022 Valencia, Spain..
    Baudot, C.
    ST Microelect, 850 Rue Jean Monnet, F-38920 Crolles, France..
    Bramerie, L.
    Univ Rennes, CNRS, FOTON, UMR 6082, F-22305 Lannion, France..
    Ozolins, Oskars
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Fotonik.
    Boeuf, F.
    ST Microelect, 850 Rue Jean Monnet, F-38920 Crolles, France..
    Vivien, L.
    Univ Paris Sud, Univ Paris Saclay, CNRS, Ctr Nanosci & Nanotechnol, F-91120 Palaiseau, France..
    Peucheret, C.
    Univ Rennes, CNRS, FOTON, UMR 6082, F-22305 Lannion, France..
    Marris-Morini, D.
    Univ Paris Sud, Univ Paris Saclay, CNRS, Ctr Nanosci & Nanotechnol, F-91120 Palaiseau, France..
    DAC-less PAM-4 generation in the O-band using a silicon Mach-Zehnder modulator2019Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, nr 7, s. 9740-9748Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate 20-Gb/s 4-level pulse amplitude modulation (PAM-4) signal generation using a silicon Mach-Zehnder modulator (MZM) in the O-band. The modulator is driven by two independent binary streams. and the PAM-4 signal is thus generated directly on the chip, avoiding the use of power-hungry digital-to-analog converters (DACs). With optimized amplitude levels of the binary signals applied to the two arms of the MZM, a pre-forward error correction (FEC) bit-error rate (BER) as low as 7.6 x 10(-7) is obtained. In comparison with a commercially available LiNbO3 modulator, the penalty is only 2 dB at the KP4 FEC threshold of 2.2 x 10(-4).

  • 234. Denker, B.
    et al.
    Galagan, B.
    Ivleva, L.
    Osiko, V.
    Sverchkov, S.
    Voronina, I.
    Hellström, Jonas E.
    KTH, Tidigare Institutioner, Fysik.
    Karlsson, Gunnar
    KTH, Tidigare Institutioner, Fysik.
    Laurell, Fredrik
    KTH, Tidigare Institutioner, Fysik.
    New crystalline material for 1.5 μm lasers: Yb,Er - Activated GdCa 4O(BO3)32004Ingår i: Advanced Solid-State Photonics: Proceedings volume, Optics Info Base, Optical Society of America, 2004, Vol. 94, s. 430-434Konferensbidrag (Refereegranskat)
    Abstract [en]

    A new crystalline medium for 1.5 μm Yb-Er lasers is proposed: GdCa 4O(BO3)3 (GdCOB). Its melting point allows crystal growth using platinum instead of iridium crucibles. Spectroscopic and laser tests of the new material are described. A maximum CW output power of 80 mW was achieved in a monolithic microchip cavity under laser diode pumping.

  • 235.
    Dev Choudhury, Bikash
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Abedin, Ahmad
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Dev, Apurba
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Sanatinia, Reza
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Anand, Srinivasan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Silicon micro-structure and ZnO nanowire hierarchical assortments for light management2013Ingår i: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 3, nr 8, s. 1039-1048Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present fabrication and optical characterization of Si microstructure-ZnO nanowire (NWs) hierarchical structures for light management. Random and periodic hierarchical structures constituting Si micro pillar or micro pyramid arrays with overgrown ZnO NWs have been fabricated. Inexpensive colloidal lithography in combination with dry and wet chemical etching is used to fabricate Si microstructures, and ZnO NWs are grown by hydrothermal synthesis. The periodic Si micro pyramid-ZnO NWs hierarchical structure shows broadband antireflection with average reflectance as low as 2.5% in the 300-1000 nm wavelength range. A tenfold enhancement in Raman intensity is observed in this structure compared to planar Si sample. These hierarchical structures with enriched optical properties and high surface to volume ratio are promising for photovoltaic (PV) and sensor applications.

  • 236.
    Dev Choudhury, Bikash
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Sahoo, Pankaj Kumar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA. Indian Institute of Technology, India.
    Sanatinia, Reza
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Andler, G.
    Stockholm University.
    Anand, Srinivasan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Swillo, Marcin
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence2015Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, nr 9, s. 2072-2075Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present experimental demonstration and analysis of enhanced surface second harmonic generation (SHG) from hexagonal arrays of silicon pillars. Three sets of Si pillar samples with truncated cone-shaped pillar arrays having periods of 500, 1000, and 2000 nm, and corresponding average diameters of 200, 585 and 1550 nm, respectively, are fabricated by colloidal lithography and plasma dry etching. We have observed strong dependence of SHG intensity on the pillar geometry. Pillar arrays with a 1000 nm period and a 585 nm average diameter give more than a one order of magnitude higher SHG signal compared to the other two samples. We theoretically verified the dependence of SHG intensity on pillar geometry by finite difference time domain simulations in terms of the surface normal E-field component. The enhanced surface SHG light can be useful for nonlinear silicon photonics, surface/interface characterization, and optical biosensing.

  • 237.
    Deyra, Loïc
    et al.
    Institut d’Optique, Univ Paris-Sud.
    Liljestrand, Charlotte
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Didierjean, Julien
    Institut d’Optique, Univ Paris-Sud.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Balembois, François
    Institut d’Optique, Univ Paris-Sud.
    Georges, Patrick
    Institut d’Optique, Univ Paris-Sud.
    High power single-crystal fiber CW 946 nm laser and blue generation based on Rubidium-doped PPKTP2013Ingår i: 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, IEEE conference proceedings, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Blue lasers have numerous applications in spectroscopy, underwater communication and material processing. Direct emission in the blue region can be achieved with laser diodes, with powers up to the watt level [1]. Higher powers require efficient laser operating around 950 nm to be frequency doubled to the blue spectrum, which usually suffer from a lower gain than conventional 1μm lasers. Generally, intracavity frequency doubling set-ups and pulsed operation are used to increase the second harmonic generation efficiency, with output powers up to 4 W in cw[2] and 1.3W in pulsed regime [3]. In the past few years, both lasers materials and non linear crystals have progressed enough to allow the very simple extracavity frequency doubling of continuous wave lasers in periodically poled materials to acceptable powers[4].

  • 238.
    Dhaka, Veer
    et al.
    Aalto University.
    Oksanen, Jani
    Aalto University.
    Jiang, Hua
    Aalto University.
    Haggren, Tuomas
    Aalto University.
    Nykänen, Antti
    Aalto University.
    Sanatinia, Reza
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Kakko, Joona-Pekko
    Aalto University.
    Huhtio, Teppo
    Aalto University.
    Ruokolainen, Janne
    Aalto University.
    Mattila, Marco
    Aalto University.
    Anand, Srinivasan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik (Stängd 20120101), Halvledarmaterial, HMA (Stängd 20120101).
    Kauppinen, Esko I
    Aalto University.
    Lipsanen, Harri
    Aalto University.
    Aluminum-Induced Photoluminescence Red Shifts in Core-Shell GaAs/AlxGa1-xAs Nanowires2013Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, nr 8, s. 3581-3588Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report a new phenomenon related to Al-induced carrier confinement at the interface in core-shell GaAs/AlxGa1-xAs nanowires grown using metal-organic vapor phase epitaxy with Au as catalyst. All AlxGa1-xAs shells strongly passivated the GaAs nanowires, but surprisingly the peak photoluminescence (PL) position and the intensity from the core were found to be a strong function of Al composition in the shell at low temperatures. Large and systematic red shifts of up to similar to 66 nm and broadening in the PL emission from the GaAs core were observed when the Al composition in the shell exceeded 3%. On the contrary, the phenomenon was observed to be considerably weaker at the room temperature. Cross-sectional transmission electron microscopy reveals Al segregation in the shell along six Al-rich radial bands displaying a 3-fold symmetry. Time-resolved PL measurements suggest the presence of indirect electron-hole transitions at the interface at higher Al composition. We discuss all possibilities including a simple shell-core-shell model using simulations where the density of interface traps increases with the Al content, thus creating a strong local electron confinement. The carrier confinement at the interface is most likely related to Al inhomogeneity and/or Al-induced traps. Our results suggest that a low Al composition in the shell is desirable in order to achieve ideal passivation in GaAs nanowires.

  • 239. Dogadaev, Anton
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Deng, Lei
    Ruepp, Sarah
    Dittmann, Lars
    Christiansen, Henrik
    Experimental and simulation analysis of the W-band SC-FDMA hybrid optical-wireless transmission2014Ingår i: IEEE Photonics Conference (IPC), San Diego, CA, USA, 2014, s. 77-78Konferensbidrag (Refereegranskat)
  • 240. Dolfi, Michele
    et al.
    Kantian, Adrian
    Bauer, Bela
    Troyer, Matthias
    Minimizing nonadiabaticities in optical-lattice loading2015Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, nr 3, artikel-id 033407Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the quest to reach lower temperatures of ultracold gases in optical-lattice experiments, nonadiabaticities during lattice loading represent one of the limiting factors that prevent the same low temperatures being reached as in experiments without lattices. Simulating the loading of a bosonic quantum gas into a one-dimensional optical lattice with and without a trap, we find that the redistribution of atomic density inside a global confining potential is by far the dominant source of heating. Based on these results we propose adjusting the trapping potential during loading to minimize changes to the density distribution. Our simulations confirm that a very simple linear interpolation of the trapping potential during loading already significantly decreases the heating of a quantum gas, and we discuss how loading protocols minimizing density redistributions can be designed.

  • 241.
    Dong, Hui
    et al.
    Nanyang Techbological University, Singapore.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Gong, Yandong
    Yan, Min
    Nanyang Techbological University, Singapore.
    Zhou, Junqiang
    Wu, Chongqing
    Measurement of polarization mode dispersion vectors in optical fibers using a virtual Mueller matrix method2007Ingår i: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 46, nr 3, s. 035007-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A virtual Mueller matrix method is proposed to measure the first- and second-order polarization mode dispersion (PMD) vectors in optical fibers. This method not only can use a large frequency step to attain low-noise PMD vector data, but also does not require knowledge of the input polarization states. Our measurement method has a simpler setup and is more accurate than the traditional Mueller matrix method.

  • 242.
    Dong, Hui
    et al.
    Nanyang Techbological University, Singapore.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Gong, Yandong
    Yan, Min
    Nanyang Techbological University, Singapore.
    Zhou, Junqiang
    Wu, Chongqing
    Virtual generalized Mueller matrix method for measurement of complex polarization-mode dispersion vector in optical fibers2007Ingår i: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 19, nr 1, s. 27-29Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A virtual generalized Mueller matrix method (VGMMM) is proposed to measure the complex polarization-mode dispersion (PMD) vector in a fiber system with polarization-dependent loss or gain. VGMMM can attain the low-noise high-resolution PMD data using a relatively large frequency step, without the knowledge of input polarization states. VGMMM combines the advantages of both matrix-based methods and differentiation-based methods and overcomes their shortcomings. Experimental results on a fiber system confirm the validity and accuracy of VGMMM.

  • 243.
    Dong, Hui
    et al.
    Nanyang Techbological University, Singapore.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Yan, Min
    Nanyang Techbological University, Singapore.
    Ning, Guoxiang
    Gong, Yandong
    Wu, Chongqing
    Generalized frequency dependence of output Stokes parameters in an optical fiber system with PMD and PDL/PDG2005Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 13, nr 22, s. 8875-8881Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dependence of output optical power, Stokes vector and degree of polarization on optical frequency is presented for an optical fiber system with both polarization mode dispersion and polarization-dependent loss or gain. The newly formulated equations are generalized for input light with arbitrary degree of polarization. The spectral resolved measurements of polarization mode dispersion using partially polarized light agree well with our theory.

  • 244.
    Dong, Hui
    et al.
    Nanyang Techbological University, Singapore.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Yan, Min
    Nanyang Techbological University, Singapore.
    Zhou, Junqiang
    Ning, Guoxiang
    Gong, Yandong
    Wu, Chongqing
    Measurement of Mueller matrix for an optical fiber system with birefringence and polarization-dependent loss or gain2007Ingår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 274, nr 1, s. 116-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In an optical fiber system with both birefringence and polarization-dependent loss or gain (PDL/G), a set of input polarization states and their corresponding outputs are deduced to fulfill some general relationships in Stokes space, by considering the fact that the Mueller matrix of such an optical fiber system meets Lorentz transformation. Then, it can be proven that the minimum number of input polarization states is three for an explicit determination of such a Mueller matrix and no independent input parameter is redundant. Based on the theoretical findings, a general and simple approach is proposed to measure the Mueller matrix. The requirements regarding the choices of three inputs are presented for achieving optimum measurement stability and accuracy. Experimental results on an optical fiber system, formed by two 10-km long single-mode fibers with an optical isolator in between, show excellent agreement with the theory.

  • 245.
    Dong, Hui
    et al.
    Nanyang Techbological University, Singapore.
    Zhou, Junqiang
    Yan, Min
    Nanyang Techbological University, Singapore.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Ma, Lin
    Gong, Yandong
    Wu, Chongqing
    Quasi-monochromatic fiber depolarizer and its application to polarization-dependent loss measurement2006Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, nr 7, s. 876-878Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We theoretically derive the relationship between the degrees of polarization (DOPs) of input and output for an optical component with polarization-dependent loss (PDL) and birefringence. Based on the theoretical result, we propose a novel depolarizer for quasi-monochromatic light that can depolarize a fully polarized light with a 50 MHz linewidth to less than 0.2% in the DOR The depolarized light is then used to measure PDL in a single-mode optical fiber link. To the best of our knowledge, our new PDL measurement method is significantly faster than all known methods. Experimental results show excellent agreement with other methods.

  • 246.
    Dong, Lin
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
    Ye, Fei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Hu, Jun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
    Popov, Sergei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
    Friberg, Ari T.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Fluorescence quenching and photobleaching in Au/Rh6G nanoassemblies: impact of competition between radiative and non-radiative decay2011Ingår i: JOURNAL OF THE EUROPEAN OPTICAL SOCIETY-RAPID PUBLICATIONS, ISSN 1990-2573, Vol. 6, s. 11019-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the study of fluorescence quenching from nanoassemblies formed by Rhodamine 6G and gold nanoparticles (Au NPs) of 2.6 nm radius. The presence of Au NPs induces long-term degradation of the photostability (photobleaching) of Rhodamine 6G used as a gain medium in a Fabry-Perot laser cavity. We found that the degradation gets profound when the Au NPs concentration is significantly increased. Calculation of the radiative rate and direct time-resolved measurement of the fluorescence decay indicates that both the decrease of radiative decay rate and increase of non-radiative decay rate are responsible for the fluorescence quenching and photostability degradation. An energy transfer from the dye molecules to gold nanoparticles is dominating within small distance between them and suppresses the quantum efficiency of Rhodamine 6G drastically. In a long time scale, the photobleaching rate was slowing down, and the laser output intensity reached a stabilized level which depends on the gold nanoparticles concentration.

  • 247.
    Drukier, Andrzej K.
    et al.
    Stockholm Univ, Dept Phys, Oskar Klein Ctr Cosmoparticle Phys, Alba Nova, S-10691 Stockholm, Sweden..
    Baum, Sebastian
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Dept Phys, Oskar Klein Ctr Cosmoparticle Phys, Alba Nova, S-10691 Stockholm, Sweden ; .
    Freese, Katherine
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Dept Phys, Oskar Klein Ctr Cosmoparticle Phys, Alba Nova, S-10691 Stockholm, Sweden ; Univ Michigan, Leinweber Ctr Theoret Phys, Ann Arbor, MI 48109 USA.
    Gorski, Maciej
    Natl Ctr Nucl Res, PL-05400 Otwock, Swierk, Poland..
    Stengel, Patrick
    Stockholm Univ, Dept Phys, Oskar Klein Ctr Cosmoparticle Phys, Alba Nova, S-10691 Stockholm, Sweden..
    Paleo-detectors: Searching for dark matter with ancient minerals2019Ingår i: PHYSICAL REVIEW D, Vol. 99, nr 4, artikel-id 043014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We explore paleo-detectors as an approach to the direct detection of weakly interacting massive particle (WIMP) dark matter radically different from conventional detectors. Instead of instrumenting a (large) target mass in a laboratory in order to observe WIMP-induced nuclear recoils in real time, the approach is to examine ancient minerals for traces of WIMP-nucleus interactions recorded over timescales as large as 1 Gyr. Here, we discuss the paleo-detector proposal in detail, including background sources and possible target materials. In order to suppress backgrounds induced by radioactive contaminants such as uranium, we propose to use minerals found in marine evaporites or in ultrabasic rocks. We estimate the sensitivity of paleo-detectors to spin-independent and spin-dependent WIMP-nucleus interactions. The sensitivity to low-mass WIMPs with masses m(chi) less than or similar to 10 GeV extends to WIMP-nucleon cross sections many orders of magnitude smaller than current upper limits. For heavier WIMPs with masses m(z) greater than or similar to 30 GeV cross sections a factor of a few to similar to 100 smaller than current upper limits can be probed by paleo-detectors.

  • 248. Drummond, Miguel V.
    et al.
    Nogueira, Rogerio N.
    Monteiro, Paulo P.
    Violas, Manuel A.
    Sterner, Carola
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Kista Photonics Research Center, KPRC.
    Fonjallaz, Pierre-Yves
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Kista Photonics Research Center, KPRC.
    Tunable Optical Dispersion Compensator Based on Power Splitting Between Two Dispersive Media2010Ingår i: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 28, nr 8, s. 1164-1175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we propose and experimentally demonstrate a novel tunable optical dispersion compensator (TODC). Dispersion compensation is achieved by splitting the input signal between two dispersive media and adding the resulting signals thereafter. Tunable compensation is attained by controlling the power splitting ratio of the input signal between both dispersive media. The frequency response of the TODC is theoretically assessed considering signal addition in the optical and electrical domains. The latter case is enabled by using optical single side-band (OSSB) modulation, which allows preserving the phase information of dispersive media output signals after direct detection. This is the only case experimentally tested, since it avoids stability problems related with coherent addition of optical signals. A TODC with a tuning range of -340 to 0 ps/nm was designed and experimentally assessed for a 40 Gb/s nonreturn-to-zero OSSB signal. The tunable power splitter consisted of an automatic polarization controller and a polarization beam splitter, which offered a tuning time lower than 150 mu s. A bit error rate lower than 10(-8) was measured on the entire compensation range with a maximum power penalty of 3.3 dB relatively to an SSB signal in back-to-back.

  • 249. Drummond, Miguel V.
    et al.
    Nogueira, Rogerio N.
    Violas, Manuel
    Monteiro, Paulo P.
    Sterner, Carola
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Kista Photonics Research Center, KPRC.
    Fonjallaz, Pierre-Yves
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Kista Photonics Research Center, KPRC.
    All-optical generation of 40 Gb/s single sideband signals using a fiber Bragg grating2010Ingår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 283, nr 12, s. 2492-2495Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, we demonstrate a reliable all-optical technique for performing optical double sideband (ODSB) to single sideband (OSSB) format conversion of a 40 Gb/s non-return-to-zero signal. It is based on the optimization of a detuned optical filter, which was implemented on a fiber Bragg grating (FBG) with a complex apodization profile. An OSSB signal with negligible distortion was obtained, as the FBG presented a nearly ideal frequency response. Higher tolerance to chromatic dispersion enabled by the OSSB signal in comparison to the ODSB signal was demonstrated on both simulation and experimental results. (C) 2010 Elsevier B.V. All rights reserved.

  • 250.
    Dubrova, Elena
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Modeling gene regulatory systems by random Boolean networks2005Ingår i: Bioengineered and Bioinspired Systems II / [ed] Carmona, RA; LinanCembrano, G, SPIE - International Society for Optical Engineering, 2005, Vol. 5839, s. 56-65Konferensbidrag (Refereegranskat)
    Abstract [en]

    A random Boolean network is a synchronous Boolean automaton with n vertices. The parameters of an RBN can be tuned so that its statistical features match the characteristics of the gene regulatory system. The number of vertices of the RBN represents the number of genes in tile cell. The number of cycles in the RBN's state space, called attractors, corresponds the number of different cell types. Attractor's length corresponds to the cell cycle time. Sensitivity of the attractors to different kind of perturbations, modeled by changing the state of a particular vertex, associated Boolean function, or network edge, reflects the stability of the cell to damage, mutations and virus attacks. In order to evaluate the attractors, their number and length have to be re-computed repeatedly. For large RBN's, searching for attractors in the O(2(n)) state space is an infeasible task. Fortunately, only a subset of vertices of an RBN, called relevant vertices, determines its dynamics. The remaining vertices are redundant. In this paper, we present an algorithm for identifying redundant vertices in RBNs which allows us to reduce the search space for computing at.tractors from O(2(n)) to Theta(2 root n). We also show how RBNs can be used for studying evolution.

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