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  • 101. Boyko, Andrey A.
    et al.
    Kostyukova, Nadezhda Y.
    Badikov, Valeriy
    Badikov, Dmitrii
    Panyutin, Vladimir
    Shevyrdyaeva, Galina
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Marchev, Georgi M.
    Kolker, Dmitry B.
    Petrov, Valentin
    Intracavity difference-frequency mixing of optical parametric oscillator signal and idler pulses in BaGa4Se72017Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 56, nr 10, s. 2783-2786Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An overall quantum conversion efficiency of 7.8% is achieved by intracavity mixing the signal and idler of a 1.064 mu m pumped Rb: PPKTP optical parametric oscillator in BaGa4Se7. In this way, a pulse energy of similar to 0.71 mJ is generated at similar to 7 mu m for a repetition rate of 100 Hz. Tuning of the mid-IR radiation is demonstrated by heating of the Rb: PPKTP crystal.

  • 102. Boyko, Andrey A.
    et al.
    Marchev, Georgi M.
    Petrov, Valentin
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Kolker, Dmitry B.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Kostyukova, Nadezhda Y.
    Intracavity-pumped, cascaded AgGaSe2 optical parametric oscillator tunable from 5.8 to 18 mu m2015Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, nr 26, s. 33460-33465Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A AgGaSe2 nonlinear crystal placed in a coupled cavity is intracavity pumped by the similar to 1.85-mu m signal pulses of a 1.064-mu m pumped Rb: PPKTP doubly-resonant optical parametric oscillator (OPO) operating at a repetition rate of 100 Hz. Using two samples cut for type-I and II phase-matching, the overall idler tunability of the singly-resonant AgGeSe2 OPO covers an unprecedented spectral range from 5.8 to similar to 18 mu m in the mid-IR.

  • 103.
    Brambilla, E.
    et al.
    Univ Insubria, Dept Sci & High Technol, Via Valleggio 11, I-22100 Como, Italy..
    Jedrkiewicz, O.
    CNR, Ist Foton & Nanotecnol, Udr Como, Via Valleggio 11, I-22100 Como, Italy..
    Gallo, Katia
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Tamosauskas, G.
    Vilnius Univ, Dept Quantum Elect, Sauletekio 10, LT-10223 Vilnius, Lithuania..
    Gatti, A.
    CNR, Ist Foton & Nanotecnol, Udr Como, Via Valleggio 11, I-22100 Como, Italy..
    Three and Four-Modes Parametric Processes in Hexagonally Poled Nonlinear Photonic Crystals2018Ingår i: OPTICS, PHOTONICS AND LASERS / [ed] Yurish, S Y, INT FREQUENCY SENSOR ASSOC-IFSA , 2018, s. 176-178Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate the properties of the field emitted through parametric down-conversion (PDC) in a nonlinear photonics crystal (NPC) with a hexagonal poling pattern, both from a theoretical point of view and with an experiment performed at the University of Insubria. Considering the high gain regime of PDC, we demonstrate the existence of concurrent PDC processes mediated by two noncollinear poling vectors which are coherently coupled and reciprocally stimulated. We find that these non-standard 3-mode and 4-mode interaction processes undergo a substantial enhancement of the parametric gain with respect to the usual 2-mode PDC, and give rise to hot spots order of magnitudes brighter than standard 2-mode fluorescence which have been observed in the source far field. We performed a complete characterization of the source spectral-angular emission, finding a very good agreement between the experiment and the theoretical predictions.

  • 104. Bratfalean, Radu
    et al.
    Gallo, Katia
    Optoelectronics Research Centre, University of Southampton (UK).
    Broderick, Neil
    Peacock, Anna
    Frequency conversion in a nonlinear photonic quasi-crystal2004Konferensbidrag (Refereegranskat)
  • 105. Bratfalean, Radu
    et al.
    Peacock, Anna
    Broderick, Neil
    Gallo, Katia
    Optoelectronics Research Centre, University of Southampton (UK).
    Lewen, Ruth
    Harmonic generation in a two-dimensional nonlinear quasi-crystal2005Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, nr 4, s. 424-426Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Second-harmonic generation in a two-dimensional nonlinear quasi-crystal is demonstrated for the first time to our knowledge. Temperature and wavelength tuning of the crystal reveal the uniformity of the pattern while angle tuning reveals the dense nature of the crystal's Fourier spectrum. These results compare well with theoretical predictions showing the excellent uniformity of the crystal and suggest that more-complicated nonlinear holograms should be possible.

  • 106. Brewer, Courtney A.
    et al.
    Brizuela, Fernando
    Wachulak, Przemyslaw
    Martz, Dale H.
    Natl. Science Foundation Engineering Research Center for Extreme Ultraviolet Science and Technology, Colorado State University.
    Chao, Weilun
    Anderson, Erik H.
    Attwood, David T.
    Vinogradov, Alexander V.
    Artyukov, Igor A.
    Ponomareko, Alexander G.
    Kondratenko, Valeriy V.
    Marconi, Mario C.
    Rocca, Jorge J.
    Menoni, Carmen S.
    Single-shot extreme ultraviolet laser imaging of nanostructures with wavelength resolution2008Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, nr 5, s. 518-520Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have demonstrated near-wavelength resolution microscopy in the extreme ultraviolet. Images of 50 nm diameter nanotubes were obtained with a single ~1 ns duration pulse from a desktop-size 46.9 nm laser. We measured the modulation transfer function of the microscope for three different numerical aperture zone plate objectives, demonstrating that 54 nm half-period structures can be resolved. The combination of near-wavelength spatial resolution and high temporal resolution opens myriad opportunities in imaging, such as the ability to directly investigate dynamics of nanoscale structures.

  • 107. Brizuela, Fernando
    et al.
    Carbajo, Sergio
    Sakdinawat, Anne
    Alessi, David
    Martz, Dale H.
    Electrical and Computer Engineering, Colorado State University.
    Wang, Yong
    Luther, Bradley
    Goldberg, Kenneth A.
    Mochi, Iacopo
    Attwood, David T.
    La Fontaine, Bruno
    Rocca, Jorge J.
    Menoni, Carmen S.
    Extreme ultraviolet laser-based table-top aerial image metrology of lithographic masks2010Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, nr 14, s. 14467-14473Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have realized the first demonstration of a table-top aerial imaging microscope capable of characterizing pattern and defect printability in extreme ultraviolet lithography masks. The microscope combines the output of a 13.2 nm wavelength, table-top, plasma-based, EUV laser with zone plate optics to mimic the imaging conditions of an EUV lithographic stepper. We have characterized the illumination of the system and performed line-edge roughness measurements on an EUVL mask. The results open a path for the development of a compact aerial imaging microscope for high-volume manufacturing.

  • 108.
    Brotons-Gisbert, Mauro
    et al.
    Heriot Watt Univ, Inst Photon & Quantum Sci, SUPA, Edinburgh EH14 4AS, Midlothian, Scotland..
    Proux, Raphael
    Heriot Watt Univ, Inst Photon & Quantum Sci, SUPA, Edinburgh EH14 4AS, Midlothian, Scotland..
    Picard, Raphael
    Heriot Watt Univ, Inst Photon & Quantum Sci, SUPA, Edinburgh EH14 4AS, Midlothian, Scotland..
    Andres-Penares, Daniel
    Univ Valencia, ICMUV, Inst Ciencia Mat, POB 2208546071, Valencia, Spain..
    Branny, Artur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Heriot Watt Univ, Inst Photon & Quantum Sci, SUPA, Edinburgh EH14 4AS, Midlothian, Scotland..
    Molina-Sanchez, Alejandro
    Univ Valencia, ICMUV, Inst Ciencia Mat, POB 2208546071, Valencia, Spain.;Int Iberian Nanotechnol Lab INL, Av Mestre Jose Veiga, P-4715330 Braga, Portugal..
    Sanchez-Royo, Juan F.
    Univ Valencia, ICMUV, Inst Ciencia Mat, POB 2208546071, Valencia, Spain..
    Gerardot, Brian D.
    Heriot Watt Univ, Inst Photon & Quantum Sci, SUPA, Edinburgh EH14 4AS, Midlothian, Scotland..
    Out-of-plane orientation of luminescent excitons in two-dimensional indium selenide2019Ingår i: NATURE COMMUNICATIONS, Vol. 10, artikel-id 3913Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Van der Waals materials offer a wide range of atomic layers with unique properties that can be easily combined to engineer novel electronic and photonic devices. A missing ingredient of the van der Waals platform is a two-dimensional crystal with naturally occurring out-of-plane luminescent dipole orientation. Here we measure the far-field photoluminescence intensity distribution of bulk InSe and two-dimensional InSe, WSe2 and MoSe2. We demonstrate, with the support of ab-initio calculations, that layered InSe flakes sustain luminescent excitons with an intrinsic out-of-plane orientation, in contrast with the in-plane orientation of dipoles we find in two-dimensional WSe2 and MoSe2 at room-temperature. These results, combined with the high tunability of the optical response and outstanding transport properties, position layered InSe as a promising semiconductor for novel optoelectronic devices, in particular for hybrid integrated photonic chips which exploit the out-of-plane dipole orientation.

  • 109.
    Brunsell, Per
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Bergsåker, Henric
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Cecconello, Marco
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Gravestijn, Robert
    KTH, Tidigare Institutioner, Fysik.
    Hedqvist, Anders
    KTH, Tidigare Institutioner, Fysik.
    Malmberg, Jenny A.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Initial results from the rebuilt EXTRAP T2R RFP device2001Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 43, nr 11, s. 1457-1470Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The EXTRAP T2R thin shell reversed-field pinch (RFP) device has recently resumed operation after a major rebuild including the replacement of the graphite armour with molybdenum limiters, a fourfold increase of the shell time constant, and the replacement of the helical coil used for the toroidal field with a conventional solenoid-type coil. Wall-conditioning using hydrogen glow discharge cleaning was instrumental for successful RFP operation. Carbon was permanently removed from the walls during the first week of operation. The initial results from RFP operation with relatively low plasma currents in the range I-p = 70-100 kA are reported. RFP discharges are sustained for more than three shell times. Significant improvements in plasma parameters are observed, compared to operation before the rebuild. There is a substantial reduction in the carbon impurity level. The electron density behaviour is more shot-to-shot reproducible. The typical density is n(e) = 0.5-1 x 10(19) m(-3). Monitors of H-alpha line radiation indicate that the plasma wall interaction is more toroidally symmetric and that there is less transient gas release from the wall. The minimum loop voltage is in the range V-t = 28-35 V, corresponding to a reduction by a factor of two to three compared to the value before the rebuild.

  • 110. Brydegaard, M.
    et al.
    Larsson, J.
    Török, S.
    Malmqvist, E.
    Zhao, G.
    Jansson, S.
    Andersson, M.
    Svanberg, S.
    Åkesson, S.
    Laurell, Frederik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Bood, J.
    Short-Wave infrared atmospheric scheimpflug lidar2018Ingår i: EPJ Web of Conferences, EDP Sciences, 2018, Vol. 176, artikel-id 01012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Atmospheric dual-band Scheimpflug lidar is demonstrated at 980 and 1550 nm. Signals are compared during three weather conditions, and the spatio-temporal resolution of the atmospheric structure is considered. The potential for aerosol classification is evaluated, and future directions are discussed.

  • 111. Budriunas, R.
    et al.
    Kucˇinskas, D.
    Stanislauskas, T.
    Gadonas, D.
    Viotti, Anne-Lise
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Varanavicˇius, A.
    Broadband noncollinear optical parametric amplification in GaSe pumped at 1.5μm2018Ingår i: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    We demonstrate broadband parametric amplification in GaSe crystal in noncollinear geometry. Seed pulses spanning 1.5-2.6μm are produced by cascaded χ(2) nonlinearity in a periodically poled Rb:KTP crystal. Amplified pulse bandwidths supporting 10-15fs transformlimited pulse durations at ~2μm central wavelength are achieved.

  • 112.
    Burvall, Anna
    et al.
    National university of Ireland, Galway.
    Barrett, Harrison H.
    University of Arizona.
    Dainty, Christopher
    National University of Ireland, Galway.
    Myers, Kyle J.
    U.S. Food and Drug Administration Laboratory for the Assessment of Medical Imaging Systems.
    Singular-value decomposition for through-focus imaging systems2006Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, nr 10, s. 2440-2448Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Singular-value decomposition (SVD) of a linear imaging system gives information on the null and measurement components of object and image and provides a method for object reconstruction from image data. We apply SVD to through-focus imaging systems that produce several two-dimensional images of a three-dimensional object. Analytical expressions for the singular functions are derived in the geometrical approximation for a telecentric, laterally shift-invariant system linear in intensity. The modes are evaluated numerically, and their accuracy confirmed. Similarly, the modes are derived and evaluated for a continuous image representing the limit of a large number of image planes.

  • 113.
    Burvall, Anna
    et al.
    National university of Ireland, Galway.
    Barrett, Harrison H.
    Dainty, Christopher
    National university of Ireland, Galway.
    Myers, Kyle J.
    Singular-value decomposition of axial systems2006Ingår i: ICO Topical meeting on optoinformation/Information Photonics 2006, 2006Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A method for reconstruction of 3D objects from 2D images, used e.g. in fluorescence microscopy, is takingseveral images along the axial direction. Singular-value decomposition is used to perform the reconstructionand determine its limits.

  • 114.
    Burvall, Anna
    et al.
    National University of Ireland, Galway.
    Daly, Elisabeth
    National University of Ireland, Galway.
    Chamot, Stephane R.
    Swiss Federal Polytechnic School of Lausanne.
    Dainty, Chris
    National University of Ireland, Galway.
    Linearity of the pyramid wavefront sensor2006Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 14, nr 25, s. 11925-11934Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The pyramid wavefront sensor is very similar to the Fourier knife-edge test, but employs dynamic modulation to quantify the phase derivative. For circular modulation, we compare approximate geometrical optics calculations, more exact diffraction calculations, and experimental results. We show that both the sinusoidal and the approximate linear relationship between wavefront derivative and wavefront sensor response can be derived rigorously from diffraction theory. We also show that geometrical, diffraction and experimental results are very similar, and conclude that the approximate geometrical predictions can be used in place of the more complex diffraction results.

  • 115.
    Burvall, Anna
    et al.
    National University of Ireland, Galway.
    Goncharov, Alexander
    National university of Irelan, Galway.
    Dainty, Christopher
    National University of Ireland, Galway.
    Diffraction analysis of lens axicons2005Ingår i: Diffractive Optics 2005, European Optical Society , 2005, s. 1-2Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Axicons, as shown in Fig. 1(a), are optical elements that produce long and narrow focallines along the optical axis, rather than the conventional focal point created by a lens. Thefocal line can be used for e.g. alignment, extending the focal depth of existing methods, orparticle trapping and transportation. Axicons are mainly produced as refractive glass cones,or as di®ractive gratings consisting of concentric circles. They can also be constructed fromordinary lenses or lens systems, referred to as lens axicons. There are several lens axicondesigns, using spherical or aspheric surfaces to produce the necessary amount of sphericalaberration.

  • 116.
    Burvall, Anna
    et al.
    National University of Ireland, Galway.
    Goncharov, Alexander
    National University of Ireland, Galway.
    Dainty, Christopher
    National university of Ireland, Galway.
    Telephoto axicon2005Ingår i: Proceedings of SPIE / [ed] Laurent Mazuray, Rolf Wartmann, SPIE - International Society for Optical Engineering, 2005Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The axicon is an optical element which creates a narrow focal line along the optical axis, unlike the single focal point produced by a lens. The long and precisely defined axicon focal line is used e.g. in alignment, or to extend the depth of focus of existing methods such as optical coherence tomography or light sectioning. Axicons are generally manufactured as refractive cones or diffractive circular gratings. They are also made as lens systems or doublet lenses, which are easier to produce. We present a design in the form of a reflective-refractive single-element device with annular aperture. This very compact system has only two surfaces, which can be spherical or aspheric depending on the quality required of the focal line. Both surfaces have reflective coatings at specific zones, providing an annular beam suitable for generating extended focal lines. One draw-back of a normal axicon is its sensitivity to the angle of illumination. Even for relatively small angles, astigmatism will broaden the focus and give it an asteroid shape. For our design, with spherical surfaces concentric about the center of the entrance pupil, the focal line remains unchanged in off-axis illumination.

  • 117.
    Burvall, Anna
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Kolacz, K.
    Jaroszewicz, Z.
    Friberg, Ari T.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Simple lens axicon2004Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, nr 25, s. 4838-4844Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the design of a cemented doublet-lens axicon made from spherical surfaces only. Compared with diffractive axicons, refractive cone axicons, and earlier lens axicons with aspheric surfaces, this element is inexpensive and easy to manufacture even with large apertures. The lens axicon is based on the deliberate use of the spherical aberration of the surfaces. The design principles of the element and its characterization, numerically and experimentally, are presented in detail. Although performance was traded for simplicity and robustness, the results show that the lens axicon has the main axicon properties: a narrow, extended line focus of relatively constant width.

  • 118.
    Burvall, Anna
    et al.
    National University of Ireland, Galway.
    Kolacz, Katarzyna
    Institute of Applied Optics, Warsaw.
    Goncharov, Alexander
    National University of Ireland, Galway.
    Jaroszewicz, Zbigniew
    Institute of Applied Optics, Warsaw.
    Dainty, Christopher
    National University of Ireland, Galway.
    Lens axicons in oblique illumination2007Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 46, nr 3, s. 312-318Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lens axicons, i.e., lenses or lens systems designed to work like axicons, can be a simple and inexpensive way of generating the characteristic axicon focal line. In the design of most lens axicons, only on-axis properties have been considered. We present the design of a lens axicon with improved off-axis characteristics. It is constructed from a singlet lens but with a double-pass feature that allows for a line of uniform width and a stop positioned to minimize aberrations. We perform off-axis analysis and experiments for this system and for another lens axicon, one designed for its on-axis characteristics. We conclude that the off-axis performance of the double-pass axicon is better than both that of an ordinary cone axicon and that of the other lens axicon.

  • 119.
    Burvall, Anna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Lundstrom, Ulf
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Takman, Per A. C.
    Larsson, Daniel H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Hertz, Hans M.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Phase retrieval in X-ray phase-contrast imaging suitable for tomography2011Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, nr 11, s. 10359-10376Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In-line phase-contrast X-ray imaging provides images where both absorption and refraction contribute. For quantitative analysis of these images, the phase needs to be retrieved numerically. There are many phase-retrieval methods available. Those suitable for phase-contrast tomography, i.e., non-iterative phase-retrieval methods that use only one image at each projection angle, all follow the same pattern though derived in different ways. We outline this pattern and use it to compare the methods to each other, considering only phase-retrieval performance and not the additional effects of tomographic reconstruction. We also outline derivations, approximations and assumptions, and show which methods are similar or identical and how they relate to each other. A simple scheme for choosing reconstruction method is presented, and numerical phase-retrieval performed for all methods.

  • 120.
    Burvall, Anna
    et al.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Martinsson, Per
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Friberg, Ari
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Communication modes applied to axicons2004Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 12, nr 3, s. 377-383Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The communication modes, which constitute a convenient method for the propagation and information analysis of optical fields, are formulated in the generalized axicon geometry. The transmitting region is the axicon’s annular aperture, and the observation domain is the optical axis containing the focal line segment. We show that in rotational symmetry one may employ the prolate spheroidal wave functions to represent the communication modes. Further, in usual circumstances the modes can be approximated by quadratic waves in the aperture domain and by sinc functions in the image domain. Both the exact communication modes and the approximate technique are confirmed numerically, with linear axicons as examples.

  • 121.
    Burvall, Anna
    et al.
    Applied Optics, Dept. of Experimental Physics, National University of Ireland, Galway, University Road, Galway, Ireland.
    Martinsson, Per
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Friberg, Ari
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Communication modes for information content analysis2004Ingår i: LFNM 2004: PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON LASER AND FIBER-OPTICAL NETWORKS MODELING / [ed] Sukhoivano, IA, IEEE conference proceedings, 2004, s. 112-114Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Approximate modes which give physical understanding for the communication modes theory,are discussed. For the geometry consisting of two line or square apertures, perpendicular to the optical axis, this approximation leads to exactly the same modes as Gabor's theory would yield.

  • 122.
    Burvall, Anna
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
    Martinsson, Per
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
    Friberg, Ari
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Optik.
    Communication modes in large-aperture approximation2007Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, nr 6, s. 611-613Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Simplified versions of the communication modes in the Fresnel domain are derived when the system apertures are large. The approximate modes, which are in the form of spherical waves and sinc functions with a spherical curvature, give physical insight into the communication modes approach and the basic limits of free-space optical communication systems. They also show that Gabor's information theory is readily derived from the communication modes.

  • 123.
    Burvall, Anna
    et al.
    National University of Ireland, Galway.
    Smith, Arlene
    National University of Ireland, Galway.
    Dainty, Christopher
    National University of Ireland, Galway.
    Elementary functions: Propagation of partially coherent light2009Ingår i: Journal of the Optical Society of America A, ISSN 0740-3232, Vol. 26, nr 7, s. 1721-1729Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The theory of propagation of partially coherent light is well known, but performing numerical calculations still presents a difficulty because of the dimensionality of the problem. We propose using a recently introduced method based on the use of elementary functions [Wald et al. Proc. SPIE6040, 59621G (2005)] to reduce the integrals to two dimensions. We formalize the method, describe its inherent assumptions and approximations, and introduce a sampling criterion for adequate interpolation. We present an analysis of some special cases, such as the Gaussian Schell-model beam, and briefly discuss generalized numerical propagation of two-dimensional field distributions.

  • 124.
    Busto, David
    et al.
    Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    Vinbladh, Jimmy
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Zhong, Shiyang
    Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    Isinger, Marcus
    Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    Nandi, Saikat
    Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    Maclot, Sylvain
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik. Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    Johnsson, Per
    Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    Gisselbrecht, Mathieu
    Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    L'Huillier, Anne
    Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    Lindroth, Eva
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Dahlström, Jan Marcus
    Lund Univ, Dept Phys, POB 118, SE-22100 Lund, Sweden..
    Fano's Propensity Rule in Angle-Resolved Attosecond Pump-Probe Photoionization2019Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, nr 13, artikel-id 133201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In a seminal article, Fano predicts that absorption of light occurs preferably with increase of angular momentum. We generalize Fano's propensity rule to laser-assisted photoionization, consisting of absorption of an extreme-ultraviolet photon followed by absorption or emission of an infrared photon. The predicted asymmetry between absorption and emission leads to incomplete quantum interference in attosecond photoelectron interferometry. It explains both the angular dependence of the photoionization time delays and the delay dependence of the photoelectron angular distributions. Our theory is verified by experimental results in Ar in the 20-40 eV range.

  • 125.
    C. Couto, Rafael
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Vaz da Cruz, Vinícius
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ertan, Emelie
    Eckert, Sebastian
    Fondell, Mattis
    Dantz, Marcus
    Kennedy, Brian
    Schmitt, Thorsten
    Pietzsch, Annette
    F. Guimarães, Freddy
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Gel’mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Odelius, Michael
    Kimberg, Victor
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Föhlisch, Alexander
    Selective gating to vibrational modes through resonant X-ray scattering2017Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, s. 14165-1-14165-7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X-ray scattering (RIXS) study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X-ray excitation to different core-excited potential energy surfaces (PESs) will act as spatial gates to selectively probe the particular ground-state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra-high resolution RIXS measurements for gas-phase water with state-of-the-art simulations.

  • 126. Cai, Y.
    et al.
    Chen, Yuntian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Eyyuboglu, H. T.
    Baykal, Y.
    Propagation of laser array beams in a turbulent atmosphere2007Ingår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 88, nr 3, s. 467-475Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The propagation of phase-locked and non-phase-locked laser array beams of radial and rectangular symmetries in a turbulent atmosphere are investigated based on the extended Huygens-Fresnel integral. The beamlet used in our paper for constructing the laser array beams is of elliptical Gaussian mode. Analytical formulae for the average irradiance of phase-locked and non-phase-locked radial and rectangular laser array beams are derived through vector integration and tensor operation. The irradiance properties of these laser array beams in a turbulent atmosphere are studied numerically. It is found that both phase-locked and non-phase-locked radial and rectangular laser array beams eventually become circular Gaussian beams in a turbulent atmosphere, which is much different from their propagation properties in free space. The propagation properties are closely related to the parameters of laser array beams and the structure constant of the turbulent atmosphere.

  • 127.
    Cai, Yangjian
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Ge, Di
    Analytical formula for a decentered elliptical Gaussian beam propagating in a turbulent atmosphere2007Ingår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 271, nr 2, s. 509-516Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Analytical formulas for the average intensity and decentered parameter of a decentered elliptical Gaussian beam (DEGB) propagating in a turbulent atmosphere are derived in a tensor form. The propagation properties of a DEGB in a turbulent atmosphere are investigated in detail, and found to be different from that in free space. Furthermore, as an application example, we investigate the propagation of a decentered elliptical flat-topped beam (DEFB) by expressing its electric field as a finite sum of DEGBs in a turbulent atmosphere. The properties of a DEGB or a DEFB in a turbulent atmosphere are closely related with the beam's parameters and the structure constant of the turbulent atmosphere.

  • 128.
    Cai, Yangjian
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Wang, Fei
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Lensless imaging with partially coherent light2007Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, nr 3, s. 205-207Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Based on the fourth-order correlation of light, lensless imaging with incoherent or partially coherent light is investigated theoretically by use of classical optical coherence theory. A novel lensless optical system for implementing imaging is proposed. The visibility and quality of the image are influenced by the coherence and transverse size of the light source. The results suggest useful imaging applications in x-ray, gamma-ray, or other wavelengths where no effective lens is available, and they have potential applications in optical metrology and holography.

  • 129.
    Calil Kores, Cristine
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. Department of Applied Physics, School of Engineering Sciences, Roslagstullsbacken 21, 10691 Stockholm, Sweden .
    Ismail, Nur
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Geskus, Dimitri
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Dijkstra, Meindert
    Bernhardi, Edward
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. Visiting scientist .
    Pollnau, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. Advanced Technology Institute, Department of Electrical and Electronic Engineering, University of Surrey, Guildford GU2 7XH, UK.
    Temperature dependence of the spectral characteristics of distributed-feedback resonators2018Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, nr 4, s. 4892-4905Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We characterize the spectral response of a distributed-feedback resonator when subject to a thermal chirp. An Al2O3 rib waveguide with a corrugated surface Bragg grating inscribed into its SiO2 top cladding is experimentally investigated. We induce a near-to-linear temperature gradient along the resonator, leading to a similar variation of the grating period, and characterize its spectral response in terms of wavelength and linewidth of the resonance peak. Simulations are carried out, showing good agreement with the experimental results and indicating that the wavelength of the resonance peak is a result only of the total accumulated phase shift. For any chirp profile we are able to calculate the reflectivities at the resonance wavelength, and this information largely explains how the linewidth of the resonance changes. This result shows that the increase in linewidth is governed by the increase of the resonator outcoupling losses. 

  • 130. Camara, Alexandre R.
    et al.
    Pereira, Joao M. B.
    Tarasenko, Oleksandr
    Margulis, Walter
    Acreo Swedish ICT.
    Carvalho, Isabel C. S.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Optical creation and erasure of the linear electrooptical effect in silica fiber2015Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, nr 14, s. 18060-18069Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the creation and erasure of the linear electrooptical effect in silicate fibers by optical poling. Carriers are released by exposure to green light and displaced with simultaneous application of an internal dc field. The second order nonlinear coefficient induced grows with poling bias. The field recorded (similar to 10(8) V/m) is comparable to that obtained through classical thermal poling of fibers. In the regime studied here, the second-order nonlinearity induced (similar to 0.06 pm/V) is limited by the field applied during poling (1.2 x 10(8) V/m). Optical erasure with high-power green light alone is very efficient. The dynamics of the writing and erasing process is discussed, and the two dimensional (2D) field distribution across the fiber is simulated. (C) 2015 Optical Society of America

  • 131. Canagasabey, Albert
    et al.
    Ibsen, Morten
    Gallo, Katia
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Gladyshev, Alexey V.
    Dianov, Evgeny M.
    Corbari, Costantino
    Kazansky, Peter G.
    Aperiodically poled silica fibers for bandwidth control of quasi-phase-matched second-harmonic generation2010Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 35, nr 5, s. 724-726Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Precise control of the bandwidth of quasi-phase-matched second-harmonic generation in silica fibers is realized through chirped-period poling. The bandwidth is expanded by a factor of 33 over a uniform-period poled fiber of the same interaction length.

  • 132.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Domain engineering in KTiOPO42005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Ferroelectric crystals are commonly used in nonlinear optics for frequency conversion of laser radiation. The quasi-phase matching (QPM) approach uses a periodically modulated nonlinearity that can be achieved by periodically inverting domains in ferroelectric crystals and allows versatile and efficient frequency conversion in the whole transparency region of the material.

    KTiOPO4 (KTP) is one of the most attractive ferroelectric non-linear optical material for periodic domain-inversion engineering due to its excellent non-linearity, high resistance for photorefractive damage, and its relatively low coercive field. A periodic structure of reversed domains can be created in the crystal by lithographic patterning with subsequent electric field poling. The performance of the periodically poled KTP crystals (PPKTP) as frequency converters rely directly upon the poling quality. Therefore, characterization methods that lead to a deeper understanding of the polarization switching process are of utmost importance.

    In this work, several techniques have been used and developed to study domain structure in KTP, both in-situ and ex-situ. The results obtained have been utilized to characterize different aspects of the polarization switching processes in KTP, both for patterned and unpatterned samples.

    It has also been demonstrated that it is possible to fabricate sub-micrometer (sub-μm) PPKTP for novel optical devices. Lithographic processes based on e-beam lithography and deep UV-laser lithography have been developed and proven useful to pattern sub- μm pitches, where the later has been the most convenient method. A poling method based on a periodical modulation of the K-stoichiometry has been developed, and it has resulted in a sub-μm domain grating with a period of 720 nm for a 1 mm thick KTP crystal. To the best of our knowledge, this is the largest domain aspect-ratio achieved for a bulk ferroelectric crystal. The sub-micrometer PPKTP samples have been used for demonstration of 6:th and 7:th QPM order backward second-harmonic generation with continuous wave laser excitation, as well as a demonstration of narrow wavelength electrically-adjustable Bragg reflectivity.

  • 133.
    Canalias, Carlota
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Hirohashi, Junji
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Polarization switching characteristics of flux grown KTiOPO4 and RbTiOPO4 at room temperature2005Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, nr 12, s. 124105-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A study of polarization-switching characteristics under an applied electrical field at room temperature is presented for flux-grown KTiOPO4 and RbTiOPO4. By optimizing the experimental conditions, we determined the coercive field and the domain-switching time quantitatively by direct observation of the switching current. For both isomorphs, the inverse of the polarization-switching time, 1/t(s), follows an exponential dependence on the applied field E in low-field regime, and a linear dependence on E in the high-field regime. Domain morphology of KTiOPO4 based on selective etching reveals laminar structures elongated in the b crystallographic direction. An estimation of the domain-wall velocity shows that the domain speed in the polar direction is, at least, two orders of magnitude larger than in the a-b plane. The velocity along the b direction is similar to 30 times larger than along the a axis.

  • 134.
    Canalias, Carlota
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Nordlöf, Mats
    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.
    Two-Dimensional Nonlinear Photonic Crystal in KTiOPO4 for CW Second Harmonic Blue Light Generation2007Ingår i: 2007 CONFERENCE ON LASERS & ELECTRO-OPTICS/QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2007), NEW YORK: IEEE , 2007, s. 404-405Konferensbidrag (Refereegranskat)
    Abstract [en]

    We report on fabrication and characterization of a nonlinear photonic crystal with a rectangular lattice in a KTiOPO4 crystal. The structure was used to demonstrate CW tunable second harmonic generation in the blue regime.

  • 135.
    Canalias, Carlota
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Counter-Propagating QPM Parametric Interactions: A Mirrorless OPO in sub-µm Periodically Poled KTiOPO42007Konferensbidrag (Refereegranskat)
    Abstract [en]

    We report on the first experimental demonstration of mirrorless optical parametric oscillation. The counter-propagating idler and signal oscillate without an external cavity in a sub-µm periodically poled KTiOPO4 crystal, reaching an efficiency of 16.5%.

  • 136.
    Canalias, Carlota
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Pasiskevicius, Valdas
    KTH, Tidigare Institutioner, Fysik.
    Clemens, Rosalie
    KTH, Tidigare Institutioner, Fysik.
    Laurell, Fredrik
    KTH, Tidigare Institutioner, Fysik.
    Submicron periodically poled flux-grown KTiOPO42003Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, nr 24, s. 4233-4235Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A submicron domain grating has been created in a bulk ferroelectric. Electron-beam lithography and electric-field poling were used to fabricate the 800 nm period grating in a 0.5-mm-thick flux-grown KTiOPO4 sample. The domain structure was characterized with an atomic force microscope and was used to demonstrate electrically amplitude adjustable Bragg reflections.

  • 137.
    Canalias, Carlota
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Fokine, Michael
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Backward quasi phase matched second harmonic generation in sub-micron periodically poled KTiOPO42005Ingår i: 2005 Conference on Lasers & Electro-Optics (CLEO), Vols 1-3, WASHINGTON: OPTICAL SOC AMERICA , 2005, s. 2264-2266Konferensbidrag (Refereegranskat)
    Abstract [en]

    1mm thick KTiOPO4 was poled with 720nm domain period by employing UV-lithography, chemical patterning and electric field poling. The structure was used to demonstrate 6 and 7 order quasi-phase matched backward second harmonic generation.

  • 138.
    Canalias, Carlota
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Fokine, Michael
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Backward quasi-phase-matched second-harmonic generation in submicrometer periodically poled flux-grown KTiOPO42005Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, nr 18, s. 181105-1-181105-3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A 1 turn thick flux-grown KTiOPO4 sample was poled with a 720 nm domain period by employing deep-UV laser lithography, chemical patterning, and electric field poling. An atomic force microscope was used to characterize the periodic domain structure. The sample was used to demonstrate sixth and seventh order quasi-phase-matched backward second-harmonic generation.

  • 139.
    Canalias, Carlota
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Pasiskevicius, Valdas
    KTH, Tidigare Institutioner, Fysik.
    Fragemann, Anna
    KTH, Tidigare Institutioner, Fysik.
    Laurell, Fredrik
    KTH, Tidigare Institutioner, Fysik.
    High-resolution domain imaging on the nonpolar y-face of periodically poled KTiOPO4 by means of atomic force microscopy2003Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, nr 4, s. 734-736Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The inverse piezoelectric effect is used to produce high-resolution images of ferroelectric domains in periodically poled KTiOPO4 crystals on their nonpolar y-face using atomic force microscopy. We demonstrate that the technique is convenient for studying the nucleation and growth of domains in a periodically poled KTiOPO4 sample.

  • 140.
    Canalias, Carlota
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Grilli, Simonetta
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    De Natale, P.
    Ferraro, P.
    In situ visualization of domain kinetics in flux grown KTiOPO4 by digital holography2007Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, nr 6, s. 064105-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fast dynamic evolution of ferroelectric domains during electric field poling in flux grown KTiOPO4 crystals was investigated online by a digital holography based technique. The dependence of the ferroelectric domain kinetics on the electric field temporal wave form and poling history was studied. High-speed imaging by means of a complementary metal-oxide-semiconductor image sensor camera allowed in situ measurement of the domain wall propagation speed under different poling conditions. The results also give evidence of the strong influence of the dielectric surface layer in this material.

  • 141.
    Canalias, Carlota
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Wang, Shunhua
    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.
    Nucleation and growth of periodic domains during electric field poling in flux-grown KTiOPO4 observed by atomic force microscopy2006Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, nr 3, s. 032905-1-032905-3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The domain structure of periodically poled KTiOPO4 crystals were studied on both the polar and nonpolar faces utilizing a voltage-modulated atomic force microscope. The measurements give information of domain nucleation, growth, and merging. Two different kind of overpoling behaviors have been observed depending on the magnitude of the applied field.

  • 142.
    Canalias, Carlota
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Viotti, A-L
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Coetzee, RS
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Liljestrand, C
    KTH.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Periodically Poled KTP with Sub-wavelength Periodicity: Nonlinear Optical Interactions with Counter Propagating Waves2018Ingår i: Optics InfoBase Conference Papers, 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present the recent development on periodically poled nonlinear crystals with subwavelength periodicities as short as 500 nm. These devices show conversion efficiencies larger than 45%. Their unique properties will be presented and discussed.

  • 143.
    Carlborg, Carl Fredrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikrosystemteknik.
    van der Wijngaart, Wouter
    KTH, Skolan för elektro- och systemteknik (EES), Mikrosystemteknik.
    Sustained Superhydrophobic Friction Reduction at High Liquid Pressures and Large Flows2011Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, nr 1, s. 487-493Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This Article introduces and experimentally explores a novel self-regulating method for reducing the friction losses in large microchannels at high liquid pressures and large liquid flows, overcoming previous limitations with regard to sustainable liquid pressure on a superhydrophobic surface. Our design of the superhydrophobic channel automatically adjusts the gas pressure in the lubricating air layer to the local liquid pressure in the channel. This is achieved by pneumatically connecting the liquid in the microchannel to the gas-pockets trapped at the channel wall through a pressure feedback channel. When liquid enters the feedback channel, it compresses the air and increases the pressure in the gas-pocket. This reduces the pressure drop over the gas liquid interface and increases the maximum sustainable liquid pressure. We define a dimensionless figure of merit for superhydropbic flows, W-F = PLD/gamma cos(theta(c)), which expresses the fluidic energy carrying capacity of a superhydrophobic microchannel. We experimentally verify that our geometry can sustain three times higher liquid pressure before collapsing, and we measured better friction-reducing properties at higher W-F values than in previous works. The design is ultimately limited in time by the gas-exchange over the gas-liquid interface at pressures exceeding the Laplace pressure. This method could be applicable for reducing near-wall laminar friction in both micro and macro scale flows.

  • 144. Carlsson, C.
    et al.
    Modh, P.
    Halonen, J.
    Schatz, Richard
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Larsson, A.
    High-frequency analog modulation of oxide confined 670-nm vertical-cavity surface-emitting lasers2004Ingår i: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 43, nr 12, s. 3138-3141Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the bandwidth limitations and the analog modulation characteristics at microwave frequencies (0.1 to 10 GHz)of a low-capacitance oxide-confined 670-nm InGaAIP vertical-cavity surface-emitting laser (VCSEL). A maximum modulation bandwidth of 6.3 GHz, limited by thermal effects, is achieved. From measurements of distortion and noise, a spurious free dynamic range (SFDR) of 100 dB Hz(2/3) is obtained at frequencies up to 2 GHz, rendering such VCSELs useful for transmission of analog signals. At higher frequencies, the SFDR drops due to the thermally limited resonance frequency.

  • 145. Carniato, S.
    et al.
    Ilakovac, V.
    Gallet, J. J.
    Kukk, E.
    Luo, Yi
    KTH, Tidigare Institutioner, Bioteknologi.
    Multidimensional transition-state theory calculations for nuclear dynamics of core-excited molecules2004Ingår 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]

    We have extended the transition-state theory to describe the dynamics of core hole excitation. This allows us to interpret the abnormally bland near-edge x-ray absorption fine structure spectrum of the gas phase benzonitrile molecule at the N 1s edge. We have brought to light different paths for the two most intensive resonances, going from the linear to the bent structure. The profile of each resonance consists of two different vibrational progressions corresponding to stretching modes and a broad continuum of bending excited states.

  • 146.
    Cecconello, Marco
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Electron density and transport in EXTRAP T2R2002Ingår i: Proceedings of the 29th European Physical Society Conference on ControlledFusion and Plasma Physics, Montreux, 2002Konferensbidrag (Övrigt vetenskapligt)
  • 147.
    Cecconello, Marco
    et al.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Brzozowski, Jerzy
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Gravestijn, Robert
    KTH, Tidigare Institutioner                               , Fysik.
    Murari, A
    Total radiation losses studies in EXTRAP T2R2001Ingår i: Proceedings of the 28th European Physical Society Conference on Controlled Fusion and Plasma Physics, Madeira, 2001Konferensbidrag (Övrigt vetenskapligt)
  • 148.
    Cecconello, Marco
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, Jenny A.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Spizzo, G.
    Chapman, B. E.
    Gravestjin, Robert M.
    KTH, Tidigare Institutioner, Fysik.
    Franz, P.
    Piovesan, P.
    Martin, P.
    Drake, James R.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Current profile modification experiments in EXTRAP T2R2004Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 46, nr 1, s. 145-161Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pulsed poloidal current drive (PPCD) experiments have been conducted in the resistive shell EXTRAP T2R reversed-field pinch experiment. During the current profile modification phase, the fluctuation level of the m = 1 internally resonant tearing modes decreases, and the velocity of these modes increases. The m = 0 modes are not affected during PPCD, although termination occurs with a burst in the m = 0 amplitude. The PPCD phase is characterized by an increase in the central electron temperature (up to 380 eV) and in the soft x-ray signal. Spectroscopic observations confirm an increase in the central electron temperature. During PPCD, the plasma poloidal beta increases to 14%, and the estimated energy confinement time doubles, reaching 380 mus. The reduction in the fluctuation level and the corresponding increase in the energy confinement time are qualitatively consistent with a reduction in parallel transport along stochastic magnetic field lines.

  • 149.
    Cecconello, Marco
    et al.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Malmberg, Jenny-Ann
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Nielsen, P
    Pasqualotto, R
    Drake, James Robert
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Study of the confinement properties in a reversed-field pinch with mode rotation and gas fuelling2002Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 44, nr 8, s. 1625-1638Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An extensive investigation of the global confinement properties in different operating scenarios in the rebuilt EXTRAP T2R reversed-field pinch (RFP) experiment is reported here. In particular, the role of a fast gas puff valve system, used to control plasma density, on confinement is studied. Without gas puffing, the electron density decays below 0.5 x 10(19) M-3. The poloidal beta varies between 5% and 15%, decreasing at large I/N. The energy confinement time ranges from 70 to 225 mus. With gas puffing, the density is sustained at n(e) approximate to 1.5 x 10(19) m(-3). However, a general slight deterioration of the plasma performances is observed for the same values of I/N: the plasma becomes cooler and more radiative. The poloidal beta is comparable to that in the scenarios without puff but the energy confinement time drops ranging from 60 to 130 mus. The fluctuation level and the energy confinement time have been found to scale with the Lundquist number as S-0.05+/-0.07 and S0.5+/-0.1, respectively. Mode rotation is typical for all the discharges and rotation velocity is observed to increase with increasing electron diamagnetic velocity.

  • 150.
    Cecconello, Marco
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, Jenny-Ann
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Sallander, Eva
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Drake, Drake James
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Self-organisation and intermittent coherent oscillations in the EXTRAP T2 reversed field pinch2002Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 65, nr 1, s. 69-75Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many reversed-field pinch (RFP) experiments exhibit a coherent oscillatory behaviour that is characteristic of discrete dynamo events and is associated with intermittent current profile self-organisation phenomena. However, in the vast majority of the discharges in the resistive shell RFP experiment EXTRAP T2, the dynamo activity does not show global, coherent oscillatory behaviour, The internally resonant tearing modes are phase-aligned and wall-locked resulting in a large localised magnetic perturbation. Equilibrium and plasma parameters have a level of high frequency fluctuations but the average values are quasi-steady. For some discharges, however, the equilibrium parameters exhibit the oscillatory behaviour characteristic of the discrete dynamo events. For these discharges, the trend observed in the tearing mode spectra, associated with the onset of the discrete relaxation event behaviour, is a relative higher amplitude of m = 0 mode activity and relative lower amplitude of the m = 1 mode activity compared with their average values. Global plasma parameters and model profile calculations for sample discharges representing the two types of relaxation dynamics are presented.

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