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  • 251.
    Dubrova, Elena
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Phylogenetic networks with edge-disjoint recombination cycles2005Ingår i: Bioengineered and Bioinspired Systems II / [ed] Carmona, RA; LinanCembrano, G, SPIE - International Society for Optical Engineering, 2005, Vol. 5839, s. 381-388Konferensbidrag (Refereegranskat)
    Abstract [en]

    Phylogenetic analysis is a branch of biology that establishes the evolutionary relationships between living organisms. The goal of phylogenetic analysis is to determine the order and approximate timing of speciation events in the evolution of a given set of species. Phylogenetic networks allow to represent evolutionary histories that include events like recombination and hybridization. In this paper, we introduce a class of phylogenetic networks called extended galled-trees in which recombination cycles share no edge. We show that the site consistency problem, which is NP-hard in general, can be solved in polynomial time for this class of phylogenetic networks.

  • 252. Duzellier, S
    et al.
    Coetzee, RS
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Dherbercourt, J-B
    Raybaut, M
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Color Centers Induced in KTiOPO4 Family Nonlinear Crystals by Exposure to Gamma-Radiation2016Konferensbidrag (Refereegranskat)
  • 253.
    Dyakov, Sergey
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO. Trinity College Dublin.
    Baldycheva, A.
    Perova, T. S.
    Li, G. V.
    Astrova, E. V.
    Gippius, N. A.
    Tikhodeev, S. G.
    Surface states in the optical spectra of two-dimensional photonic crystals with various surface terminations2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 11, s. 115126-1151268Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reflection and transmission spectra of two-dimensional photonic crystal slabs, fabricated by photoelectrochemical etching of deep macropores and trenches in Si, are investigated theoretically and experimentally. It is shown that the presence of an unstructured silicon interfacial layer between the air and the photonic crystal structure can give rise to surface (Tamm) states within the TE and TM photonic stop bands. In the presence of roughness of inner surfaces of air pores, the surface states show up as dips within the stop bands in the reflection spectrum. The calculated electromagnetic near-field distribution demonstrates the vortices between the upper pores at the frequency of the surface mode. The experimental reflection and transmission spectra are in a good agreement with theoretical calculations performed by the Fourier modal method in the scattering matrix form.

  • 254.
    Dyakov, Sergey
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO. Trinity College Dublin.
    Perova, T. S.
    Miao, C. Q.
    Xie, Y. -H
    Cherevkov, S. A.
    Baranov, A. V.
    Influence of the buffer layer properties on the intensity of Raman scattering of graphene2013Ingår i: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 44, nr 6, s. 803-809Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using a model of oscillating dipoles, we simulate the intensity of the G-band in the Raman signal from structures consisting of graphene, separated by an arbitrary buffer layer from a substrate. It is found that a structure with an optimized buffer layer refractive index and thickness exhibits a Raman signal which is nearly 50 times more intense than that from the same structure with a non-optimized buffer layer. The theoretical simulations are verified by Raman measurements on structures consisting of a layer of graphene on SiO2 and Al2O3 buffer layers. The optical contrast of the single graphene layer is calculated for an arbitrary buffer layer. It was found that both the Raman intensity and optical contrast can be maximized by varying the buffer layer thickness.

  • 255.
    Dzibrou, Dzmitry
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Complex Oxide Photonic Crystals2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Microphotonics has been offering a body of ideas to prospective applicationsin optics. Among those, the concept of photonic integrated circuits (PIC’s) has recently spurred a substantial excitement into the scientific community. Relisation of the PIC’s becomes feasible as the size shrinkage of the optical elements is accomplished. The elements based on photonic crystals (PCs) represent promising candidacy for manufacture of PIC’s. This thesis is devoted to tailoring of optical properties and advanced modelling of two types of photonic crystals: (Bi3Fe5O12/Sm3Ga5O12)m and (TiO2/Er2O3)m potentially applicable in the role optical isolators and optical amplifiers, respectively. Deposition conditions of titanium dioxide were first investigated to maximise refractive index and minimise absorption as well as surface roughness of titania films. It was done employing three routines: deposition at elevated substrate temperatures, regular annealing in thermodynamically equilibrium conditions and rapid thermal annealing (RTA). RTA at 500 oC was shown to provide the best optical performance giving a refractive index of 2.53, an absorption coefficient of 404 cm−1 and a root-mean-square surface roughness of 0.6 nm. Advanced modelling of transmittance and Faraday rotation for the PCs (Bi3Fe5O12/Sm3Ga5O12)5 and (TiO2/Er2O3)6 was done using the 4 × 4 matrix formalism of Višňovský. The simulations for the constituent materials in the forms of single films were performed using the Swanepoel and Višňovský formulae. This enabled generation of the dispersion relations for diagonal and off-diagonal elements of the permittivity tensors relating to the materials. These dispersion relations were utilised to produce dispersion relations for complex refractive indices of the materials. Integration of the complex refractive indices into the 4 × 4 matrix formalism allowed computation of transmittance and Faraday rotation of the PCs. The simulation results were found to be in a good agreement with the experimental ones proving such a simulation approach is an excellent means of engineering PCs.

  • 256.
    Dzibrou, Dzmitry
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Grishin, Alexander
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Fitting transmission and Faraday rotation spectra of Bi3Fe5O12/Sm3Ga5O12 (m) magneto-optical photonic crystals2009Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, nr 4, s. 043901-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A consistent microscopic approach is developed to simulate the transmittance and Faraday rotation in all-garnet heteroepitaxial magneto-optical photonic crystals (MOPCs). To compare the experimental and simulation results, [Bi3Fe5O12/Sm3Ga5O12](m) (BIG/SGG) MOPC designed to operate at a telecommunication wavelength lambda(res)=980 nm was chosen. It was composed of [BIG/SGG](5) and [SGG/BIG](5) distributed Bragg reflectors with a microcavity layer of BIG in between. The dispersion relations of the diagonal and off-diagonal elements of the permittivity tensor (epsilon) over cap for BIG in the electric dipole approximation were obtained from the simulation of the transmittance and Faraday rotation for a reference single layer BIG film. Revealed dispersion relations were then combined with the 4 x 4 matrix formalism for magnetic superlattices to compute transmission and Faraday rotation spectra of the MOPC. The results of numerical simulations were found to be in good agreement with the experimental ones.

  • 257.
    Dzibrou, Dzmitry
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Grishin, Alexander
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Kawasaki, H.
    Pulsed Laser Deposited TiO2Films: Tailoring optical properties2008Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, nr 23, s. 8697-8701Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    TiO2 amorphous films have been pulsed laser deposited onto glass substrates. Film characterization by X-ray diffraction, atomic force microscopy and transmission spectroscopy was performed with the aim of extracting the information on the film crystalline structure, surface roughness and optical properties. Three methods for improving film optical performance have been employed, namely deposition at elevated temperatures, post-annealing in thermodynamically equilibrium conditions and rapid thermal annealing (RTA). The best characteristics were achieved in the case of the film subjected to RTA at 500 °C: refractive index n = 2.53, absorption coefficient α = 404 cm- 1 at λ = 550 nm and rms surface roughness as low as 0.6 nm. The results obtained were found to be one of the best published so far.

  • 258.
    Ebrahimpouri, Mahsa
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    A bespoke lens for a slot log-spiral excitation2018Ingår i: IET Conference Publications, Institution of Engineering and Technology , 2018, nr CP741Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, a bespoke lens has been designed for a slot log-spiral excitation. The performance of this lens is compared with a conventional hyper-hemispherical lens. Using the bespoke lens methodology, the specific electromagnetic properties of the slot log-spiral excitation are obtained and its phase fronts are transformed to flat phase fronts by a QCTO (quasi-conformal transformation optics) technique. The performance of the lenses is evaluated with the radiation properties. The bespoke lens produces an improvement in terms of directivity and side lobe levels.

  • 259. Eckert, Sebastian
    et al.
    Vaz da Cruz, Vinicius
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Gel'mukhanov, Faris
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Ertan, Emelie
    Ignatova, Nina
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Polyutov, Sergey
    Carvalho Couto, Rafael
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Fondell, Mattis
    Dantz, Marcus
    Kennedy, Brian
    Schmitt, Thorsten
    Pietzsch, Annette
    Odelius, Michael
    Föhlisch, Alexander
    One-dimensional cuts through multidimensional potential energy surfaces by tunable X-rays2018Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The concept of the potential-energy surface (PES) and directional reaction coordinates is the backbone of ourdescription of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close-lying vibrational levels. We show here that resonant inelastic x-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground-state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center of gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one-dimensional Hamiltonian along the propagation coordinate of the core-excited wave packet. This concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground-state PES along three complementary directions for the showcase H2O molecule.

  • 260. Eckle, M
    et al.
    Eloirdi, R
    Gouder, T
    Colarieti Tosti, Massimiliano
    Wastin, F
    Rebizant, J
    Electronic structure of UCx films prepared by sputter co-deposition2004Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 334, nr 1, s. 1-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thin layers of UCx (x = 0-12) have been prepared by sputter co-deposition of uranium and carbon in an Ar atmosphere. The films were investigated in-situ by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively). Special interest was put on the evolution of the electronic structure with the composition of the films, as deduced from the U-4f, C-1s and valence region spectra. With increasing carbon content, three types of carbon species were detected according to C-1s core level line, at 282, 282.6 and 284.5 eV binding energy (BE). They are attributed to the UC, UC2 and graphite phases, respectively. The U-4f core levels do not change strongly with increasing carbon content, showing well-itinerant U-5f electrons. Similarly, valence region spectra show three types of carbon species for different UCx films, which are differentiated by their C-2p signals. A strong hybridisation between C-2p and U-5f states is detected in UC, while the C-2p signal in UC2 appears only weakly hybridised, and for higher carbon contents a pi band characteristic of graphite appears.

  • 261.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Su, Rong
    Leach, Richard
    High-precision lateral distortion measurement and correction in coherence scanning interferometry using an arbitrary surface2017Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, nr 16, s. 18703-18712Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lateral optical distortion is present in most optical imaging systems. In coherence scanning interferometry, distortion may cause field-dependent systematic errors in the measurement of surface topography. These errors become critical when high-precision surfaces, e.g. precision optics, are measured. Current calibration and correction methods for distortion require some form of calibration artefact that has a smooth local surface and a grid of high-precision manufactured features. Moreover, to ensure high accuracy and precision of the absolute and relative locations of the features of these artefacts, requires their positions to be determined using a traceable measuring instrument, e.g. a metrological atomic force microscope. Thus, the manufacturing and calibration processes for calibration artefacts are often expensive and complex. In this paper, we demonstrate for the first time the calibration and correction of optical distortion in a coherence scanning interferometer system by using an arbitrary surface that contains some deviations from flat and has some features (possibly just contamination), such that feature detection is possible. By using image processing and a self-calibration technique, a precision of a few nanometres is achieved for the distortion correction. An inexpensive metal surface, e.g. the surface of a coin, or a scratched and defected mirror, which can be easily found in a laboratory or workshop, may be used. The cost of the distortion correction with nanometre level precision is reduced to almost zero if the absolute scale is not required. Although an absolute scale is still needed to make the calibration traceable, the problem of obtaining the traceability is simplified as only a traceable measure of the distance between two arbitrary points is needed. Thus, the total cost of transferring the traceability may also be reduced significantly using the proposed method. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.

  • 262.
    Elshaari, Ali W.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Zadeh, Iman Esmaeil
    Fognini, Andreas
    Reimer, Michael E.
    Dalacu, Dan
    Poole, Philip J.
    Zwiller, Val
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. KTH, Skolan för elektro- och systemteknik (EES).
    Jöns, Klaus D.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantnanofotonik.
    On-chip single photon filtering and multiplexing in hybrid quantum photonic circuits2017Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, artikel-id 379Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantum light plays a pivotal role in modern science and future photonic applications. Since the advent of integrated quantum nanophotonics different material platforms based on III-V nanostructures-, colour centers-, and nonlinear waveguides as on-chip light sources have been investigated. Each platform has unique advantages and limitations; however, all implementations face major challenges with filtering of individual quantum states, scalable integration, deterministic multiplexing of selected quantum emitters, and on-chip excitation suppression. Here we overcome all of these challenges with a hybrid and scalable approach, where single III-V quantum emitters are positioned and deterministically integrated in a complementary metal-oxide-semiconductor-compatible photonic circuit. We demonstrate reconfigurable on-chip single-photon filtering and wavelength division multiplexing with a foot print one million times smaller than similar table-top approaches, while offering excitation suppression of more than 95 dB and efficient routing of single photons over a bandwidth of 40 nm. Our work marks an important step to harvest quantum optical technologies' full potential.

  • 263. El-Taher, Atalla
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Schatz, Richard
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Optik och Fotonik, OFO.
    Jacobsen, Gunnar
    Popov, Sergei
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Optik och Fotonik, OFO.
    Sergeyev, Sergey
    Noise characterization and transmission evaluation of unrepeated Raman amplified DP-16QAM link2015Ingår i: Optical Fiber Communication Conference, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Impairments characterization and performance evaluation of Raman amplified unrepeated DP-16QAM transmissions arc conducted, Experimental results indicate that small gain in forward direction enhance the system signal-to-noise ratio for longer reach without introducing noticeable penalty.

  • 264. Emelchenko, G.
    et al.
    Steinman, E.
    Masalov, V.
    Tereshchenko, A.
    Bazhenov, A.
    Grishin, Alex M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    1.5 μm photoluminescence of Er3+ in opal based photonic crystals2008Ingår i: Proc SPIE Int Soc Opt Eng, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    The study of the emission properties of opal-erbium oxide nanocomposites in the wide range of erbium concentrations was carried out. Erbium oxide concentration was varied from 0.25 to 16%wt. Maximal output of the photoluminescence (PL) took place at 1%wt of erbium oxide concentration. It was shown that the annealing temperatures from 600 to 900°C were too low to exhibit sufficient emission properties of the erbium-opal composites. The presence of the erbium silicates Er2SiO5 and Er 2Si2O7 in the opal-erbium nanocomposites was revealed by X-ray phase analysis. Amorphous silica in opal matrix was not crystallized at the annealing during a few hours at 1000 - 1200°C. The case of the tens hours of annealing the crystoballite phase occurred. No angle dependence of the PL intensity was observed as a result of degradation of the photonic band gap (PBG) at the annealing of the opal-erbium oxide nanocomposites. Further modification of the material processing to achieve a strong photonic band gap reflection peak near 1550 nm with high PL intensity in the opal-Er2O3 composite is running.

  • 265.
    Errando-Herranz, Carlos
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Edinger, Pierre
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik. Grenoble Institute of Technology - INP Phelma.
    Gylfason, Kristinn B.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Dynamic dispersion tuning of silicon photonicwaveguides by microelectromechanical actuation2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Efficient nonlinear silicon photonics rely on phase-matching through finewaveguide dispersion engineering. We experimentally demonstrate dynamic dispersion tuningof 800 ps/nm/km in a silicon waveguide ring resonator, by using microelectromechanicalactuation of an adjacent suspended waveguide rim.

  • 266.
    Errando-Herranz, Carlos
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Le Thomas, Nicolas
    Gylfason, Kristinn B.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Low-power optical beam steering by microelectromechanical waveguide gratingsIngår i: Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Optical beam steering is key for optical communications, laser mapping (LIDAR), and medical imaging. For these applications, integrated photonicsis an enabling technology that can provide miniaturized, lighter, lower cost, and more power efficient systems. However, common integrated photonic devices are too power demanding. Here, we experimentally demonstrate, for the first time, beam steering by microelectromechanical (MEMS)actuation of a suspended silicon photonic waveguide grating. Our device shows up to 5.6° beamsteering with 20 V actuation and a power consumption below the μW level, i.e. more than 5 orders of magnitude lower power consumption than previous thermo-optic tuning methods. The novel combination of MEMS with integrated photonics presented in this work lays ground for the next generation of power-efficient optical beam steering systems.

  • 267. Ershov, A. E.
    et al.
    Gerasimov, V. S.
    Gavrilyuk, A. P.
    Karpov, S. V.
    Zakomirnyi, Vadim I.
    KTH. Siberian Federal University, Russian Federation.
    Rasskazov, I. L.
    Polyutov, S. P.
    Thermal limiting effects in optical plasmonic waveguides2017Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 191, s. 1-6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied thermal effects occurring during excitation of optical plasmonic waveguide (OPW) in the form of linear chain of spherical Ag nanoparticles by pulsed laser radiation. It was shown that heating and subsequent melting of the first irradiated particle in a chain can significantly deteriorate the transmission efficiency of OPW that is the crucial and limiting factor and continuous operation of OPW requires cooling devices. This effect is caused by suppression of particle's surface plasmon resonance due to reaching the melting point temperature. We have determined optimal excitation parameters which do not significantly affect the transmission efficiency of OPW.

  • 268.
    Ertan, Emelie
    et al.
    Stockholm university.
    Savchenko, Viktoriia
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi. Siberian Federal University.
    Ignatova, Nina
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi. Siberian Federal University.
    da Cruz, Vinicius Vaz
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Couto, Rafael C.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Eckert, Sebastian
    Institut für Physik und Astronomie, Universität Potsdam.
    Fondell, Mattis
    Dantz, Marcus
    Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut.
    Kennedy, Brian
    Institute for Methods and Instrumentation in Synchrotron Radiation Research G- ISRR, Helmholtz-Zentrum Berlin für Materialien und Energie.
    Schmitt, Thorsten
    Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut.
    Pietzsch, Annette
    Institute for Methods and Instrumentation in Synchrotron Radiation Research G- ISRR, Helmholtz-Zentrum Berlin für Materialien und Energie.
    Föhlisch, Alexander
    Institut für Physik und Astronomie, Universität Potsdam.
    Gel'mukhanov, Faris
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Odelius, Michael
    Stockholm university.
    Kimberg, Victor
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Ultrafast dissociation features in RIXS spectra of the water molecule2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X-ray scattering spectra (RIXS) of gas phase water via the lowest dissociative core-excited state |1sO-14a11〉. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic-like peak consists of the overlapping contribution from the RIXS channels back to the ground state and to the first valence excited state |1b1-14a11〉 of the molecule. The spectral feature has signatures of ultrafast dissociation (UFD) in the core-excited state, as we show by means of ab initio calculations and time-dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic-like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core-excited state resonance, we can understand and single out the molecular and atomic-like contributions in the decay to the lowest valence-excited state. Our study is complemented by a theoretical discussion of RIXS in the case of the isotope substituted water (HDO and D2O) where the nuclear dynamics is significantly affected by the heavier fragments' mass.

  • 269.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Teoretisk och tillämpad mekanik.
    Periodiska systemets rätta form1989Ingår i: Elementa : tidskrift för matematik, fysik och kemi, ISSN 0013-5933, Vol. 72, nr 1, s. 17-20Artikel i tidskrift (Refereegranskat)
  • 270.
    Fang, Mei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    3D Magnetic Photonic Crystals: Synthesis and Characterization2010Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis presents the synthesis methods and the characterizations of magnetic Fe3O4 nanoparticles, silica spheres with Fe3O4 nanoparticles embedded, and three dimensional magnetic photonic crystals (MPCs) prepared from the spheres. The structure, material composition, magnetic and optical properties, photonic band gaps (PBGs), as well as how these properties depend on the concentration of the magnetic nanoparticles, are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), superconducting quantum interference device (SQUID), Faraday rotation (FR) and optical spectrophotometers. Well-organized, face center cubic (fcc)-structured, super-paramagnetic 3D MPCs have been obtained and their PBGs are investigated through optical spectra.

    Fe3O4 nanoparticles are synthesized by standard co-precipitation method and a rapid mixing co-precipitation method with particle size varied from 6.6 nm to 15.0 nm at different synthesis temperature (0°C ~ 100°C). The obtained Fe3O4 nanoparticles, which show crystalline structure with superparamagnetic property, are embedded into silica spheres prepared at room temperature through a sol-gel method using the hydrolysis of tetraethyl orthosilicate (TEOS) in a base solution with different concentrations. By controlling the synthesis conditions (e.g., chemicals, the ratio of chemicals and stirring time), different size of MPC spheres in range of 75 nm to 680 nm has been obtained in a narrow distribution. The sphere suspensions in ethanol are dropped on glass substrate in the permanent magnetic field to achieve well organized 3D MPCs with (111) triangular close packed crystal plane of fcc structure parallel to the surface of substrate.

    From the transmission & forward scattering spectra (TF), five PBGs have been distinguished for these MPCs and they are defined as 1st, 2nd, 3rd, 4th and 5th PBGs according to the order of peaks that appear in mathematic fitting analysis. The positions (peak wavelengths) of PBGs show sphere size dependence: with the increase of the sphere size, they increase linearly. Comparing with pure SiO2 PCs at certain sphere size, the positions of PBGs for MPCs containing moderate Fe3O4 conc. (4.3 wt. %) are at longer wavelengths. On increasing the Fe3O4 conc., however, the PBGs shift back to shorter wavelength. The PBGs shift to longer or shorter wavelength is due to the combined effect of refractive index n increasing, as well as the increase of refractive index difference Δn, which are caused by the embedded Fe3O4 nanoparticles.

    The transmission spectra (T) with varied incidence angle of p- and s- polarized light are studied, obtaining angular dependent and polarization sensitive PBGs. It is found that with the increase of the incidence angle, the 1st PBGs shift to shorter wavelength while the 3rd ones shift to longer wavelength. High Fe3O4 conc. MPCs (6.4 wt. %) show enhancement of this angular dependence. It is also found that the PBGs show dependence on the polarize direction of incident light. Normally, at a certain incidence angle the PBGs sift more for p- polarized incident light than for s-polarized light with respect to normal incidence. This polarized dependence can also be enhanced for high Fe3O4 conc. MPCs. With a high concentration of Fe3O4 nanoparticles, the polarization sensitivity of p- and s- increased.

    These PBG properties indicate applications of 3D MPCs as functional optical materials, coatings, wavelength and polarization fibers for fiber optical communications devices and dielectric sensors of magnetic field, etc..

     

  • 271.
    Fang, Mei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Takahiko, Tamaki
    Belova, Lyubov
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Rao, K. V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Co-precipitation of iron oxide nanoparticles by rapid mixingArtikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Synthesis of Magnetite appears to be a topic of continued interest because of its versatility and the variety applications. Among the chemical techniques to synthesize Fe3O4, co-precipitation approach although very common, seems to be extremely sensitive to the consequences of nucleation, growth and most of all the rate of the reaction involved. This work is an attempt to demonstrate the complexities of obtaining monodispersed nanosized Fe3O4 particles. We consider the role of rapid mixing and its consequences on co-precipitation at ice-point, room temperature and boiling water temperatures on the magnetic properties of Fe3O4. We obtained crystallites varying in the range from 6.6 nm (grown in ice-water) to 7.9 nm (grown in boiling water) as determined from the broadening of XRD diffraction peaks using the Scherrer approach. With the increase of the particle size, the saturate magnetization of iron oxides increases from 52 emu/g to 63 emu/g, and the coercivity increases from 0.5 Oe to 7.9 Oe. Layers of nanosized magnetic particles on glass substrates show unusual wavelength dependence of Faraday rotation loops which show a reversal phenomenon in the sign of the magnetization around 550.

  • 272.
    Fang, Mei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Volotinen, Tarja
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Kulkarni, S. K.
    Indian Institute of Science Education and Research, India.
    Belova, Lyubov
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Rao, K. V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Effect of Fe3O4 nanoparticles on the optical transmission properties of 3D magnetic photonic crystals2010Ingår i: Physics ReviewArtikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Magnetic and optical properties of three-dimensional magnetic photonic crystals (MPCs), consisting of silica spheres in the size range 190-680nm embedded with 8, 9 and 13 nm Fe3O4 nanoparticles, have been investigated. All the PC-films, with and without embedded magnetic nanoparticles, show five band gaps at well defined wavelengths in their optical transmission spectrum. The band gaps are found to be a linear function of the constituent sphere size in the MPC films. From the slope of this function, the deduced refractive index for the constituents in the films is found to increase with the concentration of the embedded magnetite nanoparticles. The observed shifts in the photonic band gaps PBGs in the films is qualitatively explained in terms of the variations of refractive index and the contrast index difference arising from the concentration of the embedded nanoparticles. We also find that the angular dependence of PBG positions for MPCs at small incidence angles is strongly dependent on the p- and s- polarization states of the incident light. The polarization sensitivity of PBGs to the Fe3O4 concentration is also discussed.  

  • 273.
    Fang, Mei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Volotinen, Tarja
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Kulkarni, S. K.
    Indian Institute of Science Education and Research, India.
    Belova, Lyubov
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Rao, K. V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Enhanced linear sphere size dependence of photonic band gaps for 3D nanocomposite magnetic photonic crystals2010Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Silica spheres in the size range (70-650) nm, containing embedded nano-sized magnetic iron oxide particles have been synthesized and arranged into 3D-face-centered-cubic (fcc) structured magnetic photonic crystals (MPCs) with the (111) crystal plane parallel to the glass substrate surface. Five photonic band gaps (PBGs) are observed in the optical transmission spectra measured over UV-Vis-near IR range for MPCs. The peak wavelengths of the PBGs (λC) are found to increase linearly with the sphere size (Φ). Furthermore, on embedding magnetic nanoparticles the position of PBGs is shifted to higher wavelengths. In addition, the average refractive index, 1.5 ± 0.1, obtained for the MPCs from the slopes of λC(Φ) is found to be larger than the reported value of 1.349 for pure silica PCs.

  • 274.
    Fang, Qiu
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Han, Juan
    Jiang, Jieling
    Chen, Xuebo
    Fang, Weihai
    The Conical Intersection Dominates the Generation of Tropospheric Hydroxyl Radicals from NO2 and H2O2010Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 114, nr 13, s. 4601-4608Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, we report a quantitative understanding on how to generate hydroxyl radicals from NO2 and H2O in the troposphere upon photoexcitation at 410 nm by using multiconfigurational perturbation theory and density functional theory. The conical intersections dominate the nonadiabatic relaxation processes after NO2 irradiated at similar to 410 nm in the troposphere and further control the generation of OH radical by means of hydrogen abstraction. In agreement with two-component fluorescence observed by laser techniques, there are two different photophysical relaxation channels along decreasing and increasing O-N-O angle of NO2. In the former case, the conical intersection between (B) over tilde B-2(1) and (A) over tilde B-2(2) (CI (B-2(2)/B-2(1)) first funnels NO2 out of the Franck-Condon region of (B) over tilde B-2(1) and relaxes to the (A) over tilde B-2(2) surface. Following the primary relaxation, the conical intersection between (A) over tilde B-2(2) and (X) over tilde (2)A(1) (CI(B-2(2)/(2)A(1))) drives NO2 to decay into highly vibrationally excited (X) over tilde (2)A(1) state that is more than 20 000 cm(-1) above zeroth-order vertical bar n(1),n(2),n(3) = 0 > vibrational level. In the latter case, increasing the O-N-O angle leads NO2 to relax to a minimum of (B) over tilde B-2(1) with a linear O-N-O arrangement. This minimum point is also funnel region between (B) over tilde B-2(1) and (X) over tilde (2)A(1) (CI(B-2(1)/(2)A(1))) and leads NO2 to relax into a highly vibrationally excited (X) over tilde (2)A(1) state. The high energetic level of vibrationally excited state has enough energy to overcome the barrier of hydrogen abstraction (40-50 kcal/mol) from water vapor, producing OH ((2)Pi(3/2)) radicals. The collision between NO2 and H2O molecules not only is a precondition of hydrogen abstraction but induces the faster internal conversion (CIIC) via conical intersections. The faster internal conversion favors more energy transfer from electronically excited states into highly vibrationally excited (X) over tilde (2)A(1) states. The collision (i.e., the heat motion of molecules) functions as the trigger and accelerator in the generation of OH radicals from NO2 and H2O in the troposphere.

  • 275.
    Fang, Yuntuan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Lin, Zhili
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    ENHANCEMENT OF THE DEFECT FIELD OF ONE-DIMENSIONAL PHOTONIC CRYSTALS CONTAINING epsilon- AND mu-NEGATIVE LAYERS2008Ingår i: Journal of Russian Laser Research, ISSN 1071-2836, E-ISSN 1573-8760, Vol. 29, nr 5, s. 460-465Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Employing the transfer matrix method, we study the electromagnetic field of one-dimensional photonic crystals with a defect inserted by pairs of mu-negative (MNG) and epsilon-negative (ENG) material layers. The fields within the pairs of layers and the matrix defect are independent of each other, and the whole field is their superposition. The whole defect field can be significantly enhanced by pairs of epsilon-negative and mu-negative layers. In contrast to the conventional defect modes, the intensity and volume of the defect field with pairs of epsilon-negative and mu-negative layers can be precisely adjusted.

  • 276. Fanjoux, Gil
    et al.
    Sudirman, Aziza
    Beugnot, Jean-Charles
    Furfaro, Luca
    Margulis, Walter
    Sylvestre, Thibaut
    Stimulated Raman–Kerr scattering in an integrated nonlinear optofluidic fiber arrangement2014Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, nr 18, s. 5407-5410Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We describe a novel optofluidic fiber arrangement that allows for nonlinear effects enhancement between fluids and laser light while suppressing the generation of cavitation bubbles. By filling this optofluidic system with toluene and pumping it with a nanosecond microchip laser, we demonstrate the efficient generation of a broadband Raman frequency comb spanning from 532 to more than 1000 nm. It is further shown that the Raman frequency comb dramatically broadens toward broadband continuum light due to the stimulated Raman–Kerr scattering.

  • 277. Favier, Maxime
    et al.
    Popov, Sergei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO.
    Tailored polarization eigenstates of liquid crystal SLM to generate Laguerre-Gaussian beams2014Ingår i: Proceedings - 2014 International Conference Laser Optics, LO 2014, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    We use an SLM to generate laser beams of variable orbital angular momentum, also referred as Laguerre-Gaussian beams. Input beam polarization should match local birefringence of each pixel of the SLM. We identify the beam polarization eigenstates allowing generate L-G beams of different order owing to matching variable birefringence of separate pixels. Experimental results demonstrate an excellent agreement with simulations.

  • 278.
    Fei, Chao
    et al.
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Hong, Xiaojian
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Zhang, Guowu
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Du, Ji
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Gong, Yu
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Evans, Julian
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion. Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    16.6 Gbps data rate for underwater wireless optical transmission with single laser diode achieved with discrete multi-tone and post nonlinear equalization2018Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, nr 26, s. 34060-34069Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we experimentally demonstrate a 450-nm laser underwater wireless optical transmission system by using adaptive bit-power loading discrete multi-tone (DMT) and Volterra series based post nonlinear equalization. Post nonlinear equalization mitigates the nonlinear impairment of the UWOC system. By incorporating post nonlinear equalization with a 3rd-order diagonal plane kernel, the received signal-to-noise ratio (SNR) can be improved by similar to 2 dB compared with a linear equalization method. The measured transmission capacity of the UWOC system is 16.6 Gbps over 5 m, 13.2 Gbps over 35 m, and 6.6 Gbps over 55 m tap water channel, with bit error rates (BERs) below the standard hard-decision forward error correction (HD-FEC) limit of 3.8 x 10(-3). The used electrical signal bandwidth is 2.75 GHz, corresponding to electrical spectrum efficiency of similar to 6 bit/s/Hz. The distance-datarate product reaches 462 Gbps*m at 35 m tap water transmission. To the best of our knowledge, both the data rate and distance-data rate product are the largest reported for single laser diode.

  • 279. Feifel, R.
    et al.
    Kimberg, Victor
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Baev, Alexander
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Gel'mukhanov, Faris
    KTH, Tidigare Institutioner, Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner, Bioteknologi.
    Miron, C.
    Ohrwall, G.
    Piancastelli, M. N.
    Sorensen, S. L.
    Karlsson, L.
    Svensson, S.
    Profile of resonant photoelectron spectra versus the spectral function width and photon frequency detuning2004Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 70, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The outermost, singly ionized valence state of N-2, the X (2)Sigma(g)(+) state, is investigated in detail as a function of the photon frequency bandwidth for core excitation to the N 1s-->pi(*) resonance, where the photon frequency is tuned in between the first two vibrational levels of this bound intermediate electronic state. We find a strong, nontrivial dependence of the resulting resonant photoemission spectral profile on the monochromator function width and the frequency of its peak position. For narrow bandwidth excitation we observe a well resolved vibrational fine structure in the final electron spectrum, which for somewhat broader bandwidths gets smeared out into a continuous structure. For even broader monochromator bandwidths, it converts again into a well resolved vibrational progression. In addition, spectral features appearing below the adiabatic transition energy of the ground state of N-2(+) are observed for broadband excitation. A model taking into account the interplay of the partial scattering cross section with the spectral function is presented and applied to the X (2)Sigma(g)(+) final state of N-2(+).

  • 280. Feng, Z.
    et al.
    Tang, M.
    Lin, Rui
    KTH, Skolan för informations- och kommunikationsteknik (ICT). Tongji University, School of Automotive Studies.
    Wang, R.
    Wu, Q.
    Zhang, L.
    Xu, L.
    Wang, X.
    Zhou, C.
    Wu, J.
    Zhou, S.
    Deng, L.
    Fu, S.
    Liu, D.
    Shum, P. P.
    SNR equalized optical direct-detected OFDM transmission with CAZAC equalization2015Ingår i: Conference on Lasers and Electro-Optics Europe - Technical Digest, IEEE conference proceedings, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    50Km SSMF optical direct-detected OFDM transmission with Constant Amplitude Zero Auto Correlation Sequence (CAZAC) equalization is experimentally demonstrated with over 15dB power budget. 2.5dB enhancement in sensitivity has been achieved simultaneously with 3dB PAPR suppression.

  • 281. Ferraro, P.
    et al.
    Grilli, Simonetta
    Finizio, A.
    Coppola, G.
    Iodice, M.
    Chiarini, M.
    De Nicola, S.
    Surface topography of microstructures in lithium niobate by digital holographic microscopy2004Ingår i: Measument science and technology15, ISSN 0957-0233, Vol. 15, nr 5, s. 961-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report here on the application of digital holographic microscopy as a metrological tool for the inspection and the micro-topography reconstruction of different microstructures fabricated in bulk lithium niobate by differential etching of reversed ferroelectric domain patterned crystals. These structures have a range of applications in optical ridge waveguides, alignment structures, V-grooves, micro-tips and micro-cantilever beams and precise control of the surface quality and topography is required. The technique allows us to obtain digitally a high-fidelity surface topography description of the specimen with only one image acquisition allowing us to have relatively simple and compact set-ups able to give quantitative information on object morphology. The advantages of this technique compared to traditional microscopy are discussed.

  • 282. Filippov, Andrei
    et al.
    Taher, Mamoun
    Shah, Faiz Ullah
    Glavatskih, Sergei
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.). Ghent University, Belgium .
    Antzutkin, Oleg N.
    The effect of the cation alkyl chain length on density and diffusion in dialkylpyrrolidinium bis(mandelato)borate ionic liquids2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 48, s. 26798-26805Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The physicochemical properties of ionic liquids are strongly affected by the selective combination of the cations and anions comprising the ionic liquid. In particular, the length of the alkyl chains of ions has a clear influence on the ionic liquid's performance. In this paper, we study the self-diffusion of ions in a series of halogen-free boron-based ionic liquids (hf-BILs) containing bis(mandelato)borate anions and dialkylpyrrolidinium cations with long alkyl chains CnH2n+1 with n from 4 to 14 within a temperature range of 293-373 K. It was found that the hf-BILs with n = 4-7 have very similar diffusion coefficients, while hf-BILs with n = 10-14 exhibit two liquid sub-phases in almost the entire temperature range studied (293-353 K). Both liquid sub-phases differ in their diffusion coefficients, while values of the slower diffusion coefficients are close to those of hf-BILs with shorter alkyl chains. To explain the particular dependence of diffusion on the alkyl chain length, we examined the densities of the hf-BILs studied here. It was shown that the dependence of the density on the number of CH2 groups in long alkyl chains of cations can be accurately described using a "mosaic type'' model, where regions of long alkyl chains of cations (named 'aliphatic' regions) and the residual chemical moieties in both cations and anions (named 'ionic' regions) give additive contributions. Changes in density due to an increase in temperature and the number of CH2 groups in the long alkyl chains of cations are determined predominantly by changes in the free volume of the 'ionic' regions, while 'aliphatic' regions are already highly compressed by van der Waals forces, which results in only infinitesimal changes in their free volumes with temperature.

  • 283.
    Fognini, A.
    et al.
    Delft Univ Technol, Kavli Inst Nanosci Delft, NL-2628 CJ Delft, Netherlands. hmadi, A..
    Ahmadi, A.
    Zeeshan, M.
    Fokkens, J. T.
    Gibson, S. J.
    Sherlekar, N.
    Daley, S. J.
    Dalacu, D.
    Poole, P. J.
    Jöns, Klaus D.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Zwiller, Val
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Reimer, M. E.
    Dephasing Free Photon Entanglement with a Quantum Dot2019Ingår i: ACS Photonics, E-ISSN 2330-4022, Vol. 6, nr 7, s. 1656-1663Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Generation of photon pairs from quantum dots with near-unity entanglement fidelity has been a long-standing scientific challenge. It is generally thought that the nuclear spins limit the entanglement fidelity through spin flip dephasing processes. However, this assumption lacks experimental support. Here, we show two-photon entanglement with negligible dephasing from an indium rich single quantum dot comprising a nuclear spin of 9/2 when excited quasi-resonantly. This finding is based on a significantly close match between our entanglement measurements and our model that assumes no dephasing and takes into account the detection system's timing jitter and dark counts. We suggest that neglecting the detection system is responsible for the degradation of the measured entanglement fidelity in the past and not the nuclear spins. Therefore, the key to unity entanglement from quantum dots comprises a resonant excitation scheme and a detection system with ultralow timing jitter and dark counts.

  • 284.
    Fokine, Michael
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Manipulating glass for photonics2009Ingår i: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, ISSN 1862-6300, Vol. 206, nr 5, s. 880-884Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A generalized concept for local manipulation of three-dimensional glass materials is described. The basic principle is to use means to deposit energy into the material to enable localized and selective changes in the bond structure of the glass matrix, causing a localized modification of the thermal equilibrium properties of the material. The different regions of the glass will then behave differently when the sample is subsequently heated homogeneously. If the difference in the thermal dynamics between modified and un-modified regions is significant, thermal treatment of the material can result in a self-organizing structure. The aim here is to provide a generalized concept of differential systems and self-organizing structures, using chemical composition Bragg gratings as an example. In this case, differential diffusion results in self-organizing structures consisting of a variation of the chemical composition, with compositional features smaller than 250 nm.

  • 285.
    Fokine, Michael
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Chen, Yiting
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik.
    Wang, Jing
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik.
    Hao, Jiaming
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik.
    Meiser, Niels
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik.
    Optical Characterization of Plasmonic Metamaterial Absorber2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    A reflectance/transmittance experiment setup to characterize a sub-wavelength, wide-angle, ultrathin metamaterial absorber at optical frequency regime is shown, and the measured results are presented.

  • 286.
    Fokine, Michael
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Hoon, Jang
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    M. P. Goueva, Paula
    Pontifícia Universidade Católica do Rio de Janeiro.
    M. B. Braga, Arthur
    Pontifícia Universidade Católica do Rio de Janeiro.
    C. S. Carvalho, Isabel
    Pontifícia Universidade Católica do Rio de Janeiro.
    Spectral features of specular reflection from nanoparticle films2010Ingår i: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 8, nr 9, s. 2673-2675Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work we analyze the internal reflection (Fresnel reflection) from Au nanoparticles on the end face of optical fibers. We demonstrate that changes in the refractive index of the surrounding medium can be detected by shifts in the reflection spectra associated with changes in the Localized Surface Plasmon Resonance of the Au-Nanoparticles. The spectral response is simulated using a model based on the interference in multilayer structures and can be described by transfer-matrix method.

  • 287.
    Fokine, Michael
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Theodosiou, Antreas
    Song, Seunghan
    Hawkins, Thomas
    Ballato, John
    Kalli, Kyriacos
    Gibson, Ursula J.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Laser structuring, stress modification and Bragg grating inscription in silicon-core glass fibers2017Ingår i: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, nr 5, s. 1589-1597Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Semiconductor core fibers have numerous potential applications in optoelectronics and photonics, and the key to realizing these opportunities is controlled processing of the material. We present results on laser treatments for manipulating the core structure as well as the glass cladding. More specifically, using quasi-CW 10.6 mu m radiation, the clad glass can be softened and the core can be controllably melted. This is shown to permit tapering, localized formation of optical resonators, and stress modification of the as-drawn fiber and structures within it. Shown for the first time to the authors' knowledge are Bragg gratings written by modification of the silicon/glass interface using fs laser illumination at 517 nm. The cores of these fibers show stress alterations, with indications of quasi-periodic stress relief in the glass.

  • 288. Fontaine, N. K.
    et al.
    Baek, J. -H
    Ji, C.
    Broeke, R. G.
    Zhou, X.
    Seo, S. -W
    Soares, F. M.
    Shearn, M.
    Scherer, A.
    Olsson, Fredrik E.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Lourdudoss, Sebastian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Liu, K. Y.
    Tsang, W. T.
    Yoo, S. J. B.
    Monolithically integratable colliding pulse modelocked laser source for O-CDMA photonic chip development2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    We demonstrate modelocking of a colliding-pulse mode-locked laser formed by 3-μm-deep etched-mirrors on an InP platform for integration with passive waveguide components. Timing jitter of 243 fs and pulse width of 10 ps were measured.

  • 289.
    Fragemann, Anna
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Optical parametric amplification with periodically poled KTiOPO42005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis explores the use of engineered nonlinear crystals from the KTiOPO4 (KTP) family as the gain material in optical parametric amplifiers (OPAs), with the aim to achieve more knowledge about the benefits and limitations of these devices. The work aims further at extending the possible applications of OPAs by constructing and investigating several efficient and well performing amplifiers.

    An OPA consists of a strong pump source, which transfers its energy to a weak seed beam while propagating through a nonlinear crystal. The crystals employed in this work are members of the KTP family, which are attractive due to their large nonlinear coefficients, high resistance to damage and wide transparency range. The flexibility of OPAs with respect to different wavelength regions and pulse regimes was examined by employing various dissimilar seed and pump sources.

    The possibility to adapt an OPA to a specific pump and seed wavelength and achieve efficient energy conversion between the beams, originates from quasi-phasematching, which is achieved in periodically poled (PP) nonlinear crystals. Quasi-phasematched samples can be obtained by changing the position of certain atoms in a ferroelectric crystal and thereby reversing the spontaneous polarisation.

    In this thesis several material properties of PP crystals from the KTP family were examined. The wavelength and temperature dispersion of the refractive index were determined for PP RbTiOPO4, which is essential for future use of this material. Another experiment helped to increase the insight into the volumes close to domain walls in PP crystals

    Further, several OPAs were built and their ability to efficiently amplify the seed beam without changing its spectral or spatial properties was studied. Small signal gains of up to 55 dB and conversion efficiencies of more than 35 % were achieved for single pass arrangements employing 8 mm long PPKTP crystals. Apart from constructing three setups, which generated powerful nanosecond, picosecond and femtosecond pulses, the possibility to amplify broadband signals was investigated. An increase of the OPA bandwidth by a factor of approximately three was achieved in a noncollinear configuration.

  • 290.
    Fragemann, Anna
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Pasiskevicius, Valdas
    KTH, Tidigare Institutioner, Fysik.
    Karlsson, Gunnar
    KTH, Tidigare Institutioner, Fysik.
    Laurell, Fredrik
    KTH, Tidigare Institutioner, Fysik.
    High-peak power nanosecond optical parametric amplifier with periodically poled KTP2003Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 11, nr 11, s. 1297-1302Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A two-stage optical parametric amplifier generating 5 ns 208 kW peak power pulses in the spectral region at 1.535 mum in a diffraction-limited beam was realized in a single periodically poled KTP crystal. The maximum small-signal gain for the two stages reached 75dB and the total conversion efficiency was 30%. An analysis of the small-signal gain dependence on the M-2 of the pump beam is presented for the collinear and noncollinear OPA. Efficient spectral broadening of the signal was demonstrated in short pieces of single-mode telecommunication fiber.

  • 291.
    Fragemann, Anna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Broadband nondegenerate optical parametric amplification in the mid infrared with periodically poled KTiOPO42005Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, nr 17, s. 2296-2298Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We theoretically and experimentally demonstrate that the bandwidth in a nondegenerate optical parametric amplifier can be substantially increased by noncollinear interaction in a quasi-phase-matched single-periodicity structure. Broadband amplification of signals between 1540 and 1720 nm was realized in periodically poled KTiOPO4. The achieved signal bandwidth of 6.9 THz at 1680 nm is large enough to accommodate sub-100 fs optical pulses.

  • 292.
    Fragemann, Anna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Broadband optical parametric amplification in the Mid-infrared spectral region with periodically poled KTiOPO42006Ingår i: CLEO/QELS 2006, Optical Society of America, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    Angle-tunable PPKTP OPA for signals between 1540 nm and 1720 nm was realized in a single periodicity QPM grating. The noncollinear OPA configuration increased the bandwidth from 2.4 THz to 6.9 THz.

  • 293.
    Fragemann, Anna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Broadband optical parametric amplification in the mid-infrared spectral region with periodically poled KTiOPO42005Ingår i: 2005 Conference on Lasers & Electro-Optics (CLEO), Vols 1-3, 2005, s. 1297-1299Konferensbidrag (Refereegranskat)
    Abstract [en]

    Angle-tunable PPKTP OPA for signals between 1540 nm and 1720 nm was realized in a single periodicity QPM grating. The noncollinear OPA configuration increased the bandwidth from 2.4 THz to 6.9 THz.

  • 294.
    Fragemann, Anna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Broadband optical-parametrie-amplification in the mid-infrared spectral region with periodically poled KTiOPO42005Konferensbidrag (Refereegranskat)
    Abstract [en]

    Angle-tunable PPKTP OPA for signals between 1540 nm and 1720 nm was realized in a single periodicity QPM grating. Noncollinear OPA configuration increased the bandwidth from 2.4 THz to 6.9 THz.

  • 295.
    Fragemann, Anna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Optical parametric amplification of a gain-switched picosecond laser diode2005Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 13, nr 17, s. 6482-6489Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optical parametric amplification, employing periodically poled KTiOPO4 as the gain medium, was used to amplify radiation emitted by a gain-switched laser diode. The pulses, which had durations between 20 ps and 2 ns, were amplified with up to 50 dB in a double stage set-up and reached pulse energies of 1 and 23 mu J, respectively.

  • 296.
    Fragemann, Anna
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Pasiskevicius, Valdas
    KTH, Tidigare Institutioner, Fysik.
    Laurell, Fredrik
    KTH, Tidigare Institutioner, Fysik.
    Second-order nonlinearities in the domain walls of periodically poled KTiOPO42004Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, nr 3, s. 375-377Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The domain wall regions in periodically poled KTiOPO4 crystals were examined and found to give rise to phasematched second harmonic generation in the Cerenkov directions. This phenomenon is caused by the nonlinear coefficients d(11) and d(12), which are not present in single domain regions, but are nonzero at and close to domain walls. The appearance of these nonlinearities is attributed to strain, produced by the domain inversion process and results in the creation of a dc piezoelectric field.

  • 297.
    Fragemann, Anna
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Pasiskevicius, Valdas
    KTH, Tidigare Institutioner, Fysik.
    Nordborg, Jenni
    KTH, Tidigare Institutioner, Fysik.
    Hellström, Jonas
    KTH, Tidigare Institutioner, Fysik.
    Karlsson, Håkan
    KTH, Tidigare Institutioner, Fysik.
    Laurell, Fredrik
    KTH, Tidigare Institutioner, Fysik.
    Frequency converters from visible to mid-infrared with periodically poled RbTiOPO42003Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, nr 15, s. 3090-3092Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electric-field poling has been used to fabricate quasi-phase-matched frequency converters in RbTiOPO4. A more accurate Sellmeier equation has been obtained for wavelengths between 0.43 and 3.4 mum. The dispersion of the thermo-optic coefficient for n(z) refractive index has been derived in the near- to mid-infrared spectral region. The nonlinear performance of periodically poled RbTiOPO4 obtained in the infrared optical parametric devices is comparable to that of periodically poled KTiOPO4.

  • 298. Franciscangelis, C.
    et al.
    Margulis, W.
    Floridia, C.
    Rosolem, J. B.
    Salgado, F. C.
    Nyman, T.
    Petersson, M.
    Hallander, P.
    Hallström, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Söderquist, I.
    Fruett, F.
    Vibration measurement on composite material with embedded optical fiber based on phase-OTDR2017Ingår i: Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2017 / [ed] Lynch, J P, SPIE - International Society for Optical Engineering, 2017, Vol. 10168, artikel-id 101683QKonferensbidrag (Refereegranskat)
    Abstract [en]

    Distributed sensors based on phase-optical time-domain reflectometry (phase-OTDR) are suitable for aircraft health monitoring due to electromagnetic interference immunity, small dimensions, low weight and flexibility. These features allow the fiber embedment into aircraft structures in a nearly non-intrusive way to measure vibrations along its length. The capability of measuring vibrations on avionics structures is of interest for what concerns the study of material fatigue or the occurrence of undesirable phenomena like flutter. In this work, we employed the phase-OTDR technique to measure vibrations ranging from some dozens of Hz to kHz in two layers of composite material board with embedded polyimide coating 0.24 numerical aperture single-mode optical fiber.

  • 299. Francke, T
    et al.
    Peskov, Vladimir
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Photosensitive gaseous detectors and their applications2004Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 525, nr 1-2, s. 1-5Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reviews a large and important class of position sensitive detectors called photosensitive gaseous detectors (PGDs). Their main application rests in the imaging of UV photons. There are however, successful efforts to extend their sensitivity to visible light. With some modifications, PGDs can also be used in the imaging of X-rays and particles.

  • 300. Francke, T
    et al.
    Peskov, Vladimir
    KTH, Tidigare Institutioner, Fysik.
    Rodionov, I
    Fonte, P
    High rate (up to 10(5) Hz/cm(2)), high position resolution (30 mu m) photosensitive RPCs2004Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 533, nr 1-2, s. 163-168Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In many applications there is a need for high position resolution VUV and UV imagers. For these applications we have developed and successfully tested 1D and 2D VUV imaging detectors based on microgap RPCs. Two versions of these detectors were extensively tested: one filled with photosensitive vapours and the other one with the GaAs cathode coated by a 400 nm thick CsI layer. The main feature of these detectors is the high position resolution-30 mum in digital form. Additionally, it is spark-protected and can operate at high counting rates (up to 10(5) Hz/cm(2)). In this study the results in application for these detectors for spectroscopy are presented.

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