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Now showing items 1 - 16 of 56

  • Temperature dependent non-monotonic bands shift in ZrTe5

    Manzoni, G.   Crepaldi, A.   Autes, G.   Sterzi, A.   Cilento, F.   Akrap, A.   Vobornik, I.   Gragnaniello, L.   Bugnon, Ph.   Fonin, M.   Berger, H.   Zacchigna, M.   Yazyev, O. V.   Parmigiani, F.  

    The electronic structure of ZrTe5 has been matter of renewed interest aimed at clarifying, along with its topological character, the temperature dependence of the unusual transport properties of this material. Here, we report an extensive high resolution Angle Resolved Photoelectron Spectroscopy (ARPES) study unveiling a non-monotonic shift of the bands, when the sample temperature is varied between 16K and 300K. Moreover, the present conventional ARPES and circularly dichroic ARPES measurements reveal the presence of two states at the top of the valence band. The strong ARPES dichroic signal detected in proximity of the Fermi energy has been interpreted as the indication of the presence of spin polarized states, in agreement with the predicted strong topological character of this material. (c) 2016 Elsevier B.V. All rights reserved.
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  • MagneDyn: the future beamline for ultrafast magnetodynamical studies at FERMI

    Svetina, C.   Dell'Angela, M.   Mahne, N.   Malvestuto, M.   Parmigiani, F.   Raimondi, L.   Zangrando, M.  

    The future beamline Magneto Dynamics (MagneDyn) will be devoted to study the electronic states and the local magnetic properties of excited and transient states of complex systems by means of the time-resolved X-ray absorption spectroscopy (TR-XAS) technique. The beamline will use the high energy source at FERMI covering the wavelength range from 60 nm down to 1.3 nm. An on-line photon energy spectrometer will allow to measure the spectrum with high resolution while delivering most of the beam to the end-stations. Downstream the beam will be possibly split and delayed, by means of a delay line, and then focused with a set of active KB mirrors. These mirrors will be able to focus the radiation in one of the two MagneDyn experimental chambers: the electro-magnet end-station and the Resonant Inelastic X-ray Scattering (RIXS) end-station. After an introduction of MagneDyn scientific case, we will discuss the layout showing the expected performances of the beamline.
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  • Phase sensitive amplification in a highly nonlinear lead-silicate fiber

    Ettabib, M.A.   Jones, L.   Kakande, J.   Slavi'k, R.   Parmigiani, F.   Xian Feng   Poletti, F.   Ponzo, G.M.   Jindan Shi   Petrovich, M.N.   Loh, W.H.   Petropoulos, P.   Richardson, D.J.  

    We experimentally demonstrate phase-sensitive amplification in a highly nonlinear and low-dispersion lead-silicate W-type fiber. A phase-sensitive gain variation of 6 dB was observed in a 1.56-m sample of the fiber for a total input pump power of 27.7 dBm.
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  • All-Optical Grooming for 100 Gbit/s Ethernet

    Leuthold, J.   Bonk, R.   Vorreau, P.   Sygletos, S.   Hillerkuss, D.   Freude, W.   Zarris, G.   Simeonidou, D.   Kouloumentas, C.   Spyropoulou, M.   Tomkos, I.   Parmigiani, F.   Petropoulos, P.   Richardson, D. J.   Weerasuriya, R.   Ibrahim, S.   Ellis, A. D.   Morais, R.   Monteiro, P.   Ben Ezra, S.   Tsadka, S.  

    A regenerative optical grooming switch for interconnecting 100 Gbit/s networks with lower bit-rate networks and switching functionality in time, space and wavelength domain is demonstrated. Lab and field demonstrations show the feasibility of the new concept. Q-factors above 20 dB are reported.
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  • Multi-Channel Phase Regenerator Based on Polarization-Assisted Phase-Sensitive Amplification

    Parmigiani, F.   Bottrill, K. R. H.   Slavik, R.   Richardson, D. J.   Petropoulos, P.  

    We propose and demonstrate simultaneous phase regeneration of six nonreturn-to-zero binary phase shift keying signals in a single nonlinear medium. The regenerating system, which exhibits binary steplike phase transfer functions, uses four-wave mixing in degenerate dual-pump vector parametric amplifiers implemented in the same nonlinear optical fiber, followed by polarization filtering. Bit-error-ratio measurements confirm optical-signal-to-ratio improvement and negligible crosstalk across all the regenerated channels, which were impaired at the regenerator input by broadband phase noise.
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  • The FERMI@Elettra FEL Photon Transport System

    Cocco, D.   Abrami, A.   Bianco, A.   Cudin, I.   Fava, C.   Giuressi, D.   Godnig, R.   Parmigiani, F.   Rumiz, L.   Sergo, R.   Svetina, C.   Zangrando, M.  

    The FERMI@Elettra free electron laser (FEL) user facility is currently under construction at the Sincrotrone Trieste laboratory in Trieste (Italy). It is a based on a seeded scheme that will provide an almost perfect transform limited beam and fully spatial coherent. It will cover the wavelength range from 100 to about 3 nm and in a short future down to 1 nm (by using higher harmonics). It is expected to be fully operative in the late summer of 2010. In this presentation we will report the layout of the photon beam diagnostics section with the preliminary tests, the radiation transport system to the experimental area, and the experimental hall facilities. A particular emphasis will be given to the optical solution and constrains due to the need of preserving the wave front and to avoid damage on the different optical elements, including slits, mirrors, gratings and all the diagnostic facilities. One of the main problems will be the necessity of using very large grazing incidence angle (up to 45 degrees) on multilayers and single coating mirrors. These elements are mandatory to perform the transient grating experiments and to realize the delay lines, where time delay up to 1 nsec are required. This issue poses a serious problem in terms of energy density delivered and adsorbed by the optics and great care must be taken into the choice of the proper multilayer materials. Some studies on the reflectivity of multilayers and Carbon coated mirrors will be reported as well as the diagnostic tools to monitor the quality of the optics in operative conditions.
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  • Surface and bulk contribution to Cu(111) quantum efficiency RID G-2395-2010

    Pedersoli, E.   Greaves, C. M. R.   Wan, W.   Coleman-Smith, C.   Padmore, H. A.   Pagliara, S.   Cartella, A.   Lamarca, F.   Ferrini, G.   Galimberti, G.   Montagnese, M.   dal Conte, S.   Parmigiani, F.  

    The quantum efficiency (QE) of Cu(111) is measured for different impinging light angles with photon energies just above the work function. We observe that the vectorial photoelectric effect, an enhancement of the QE due to illumination with light with an electric vector perpendicular to the sample surface, is stronger in the more surface sensitive regime. This can be explained by a contribution to photoemission due to the variation in the electromagnetic potential at the surface. The contributions of bulk and surface electrons can then be determined.
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  • Time-division-multiplexing using pulse position locking for 100 Gb/s applications

    Chow, C. W.   Ellis, A. D.   Parmigiani, F.  

    Recently, there is a great interest in pushing communication technologies to 100 Gb/s. However, there are still many challenges to perform high speed (> 40 Gb/s) clock and data recovery, and data time-division-multiplexing (TDM). Here, we propose and numerically analyze an asynchronous optical packet retimer using parabolic or sinusoidal phase modulation and linear dispersion. This scheme is named pulse position locking (PPL). Numerical simulation shows that this scheme can effectively resynchronize input signals with arbitrary delays to the local clock, and reduce input jitter. The scheme can also be applied to TDM 10 Gb/s and 40 Gb/s signals to over 100 Gb/s. (C) 2009 Optical Society of America
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  • An Efficient Wavelength Converter Exploiting a Grating-Based Saw-Tooth Pulse Shaper

    Parmigiani, F.   Ibsen, M.   Ng, T.T.   Provost, L.   Petropoulos, P.   Richardson, D.J.  

    We experimentally demonstrate the generation of picosecond triangular optical pulses using a superstructured fiber Bragg grating and show experimentally that use of this pulse shape can provide a three-fold improvement in conversion efficiency relative to the use of Gaussian pulses with similar pulsewidths when used in a wavelength conversion scheme based on self-phase modulation and subsequent offset filtering.
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  • Extreme ultraviolet resonant inelastic X-ray scattering (RIXS) at a seeded free-electron laser

    Dell'Angela, M.   Hieke, F.   Malvestuto, M.   Sturari, L.   Bajt, S.   Kozhevnikov, I. V.   Ratanapreechachai, J.   Caretta, A.   Casarin, B.   Glerean, F.   Kalashnikova, A. M.   Pisarev, R. V.   Chuang, Y. -D.   Manzoni, G.   Cilento, F.   Mincigrucci, R.   Simoncig, A.   Principi, E.   Masciovecchio, C.   Raimondi, L.   Mahne, N.   Svetina, C.   Zangrando, M.   Passuello, R.   Gaio, G.   Prica, M.   Scarcia, M.   Kourousias, G.   Borghes, R.   Giannessi, L.   Wurth, W.   Parmigiani, F.  

    In the past few years, we have been witnessing an increased interest for studying materials properties under non-equilibrium conditions. Several well established spectroscopies for experiments in the energy domain have been successfully adapted to the time domain with sub-picosecond time resolution. Here we show the realization of high resolution resonant inelastic X-ray scattering (RIXS) with a stable ultrashort X-ray source such as an externally seeded free electron laser (FEL). We have designed and constructed a RIXS experimental endstation that allowed us to successfully measure the d-d excitations in KCoF3 single crystals at the cobalt M-2,M-3-edge at FERMI FEL (Elettra-Sincrotrone Trieste, Italy). The FEL-RIXS spectra show an excellent agreement with the ones obtained from the same samples at the MERIXS endstation of the MERLIN beamline at the Advanced Light Source storage ring (Berkeley, USA). We established experimental protocols for performing time resolved RIXS experiments at a FEL source to avoid X ray-induced sample damage, while retaining comparable acquisition time to the synchrotron based measurements. Finally, we measured and modelled the influence of the FEL mixed electromagnetic modes, also present in externally seeded FELs, and the beam transport with similar to 120 meV experimental resolution achieved in the presented RIXS setup.
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  • Probing band parity inversion in the topological insulator GeBi2Te4 by linear dichroism in ARPES

    Sterzi, A.   Manzoni, G.   Crepaldi, A.   Cilento, F.   Zacchigna, M.   Leclerc, M.   Bugnon, Ph.   Magrez, A.   Berger, H.   Petaccia, L.   Parmigiani, F.  

    Here we report on experiments performed by linear-dichroism angle resolved photoelectron spectroscopy (LD-ARPES) on septuple layers (SL) topological insulator GeBi2Te4. The linear dichroic signals, both for the valence band states and in the topologically protected surface state are interpreted as a probe of the symmetry of the states. The observation of a change in the LD-ARPES spectrum at the top of VB is attributed to the band parity inversion which is predicted by theory for all materials entering the topologically protected phase. Finally, the opening of a gap in the surface state dispersion along the non-high symmetry direction is reported. This is proposed to originated from the interaction between the surface state and the VB, leading to the formation of surface resonances. (C) 2018 Elsevier B.V. All rights reserved.
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  • Stable and Efficient Generation of High Repetition Rate (> 160 GHz) Subpicosecond Optical Pulses

    Slavik, R.   Parmigiani, F.   Gruner-Nielsen, L.   Jakobsen, D.   Herstrom, S.   Petropoulos, P.   Richardson, D. J.  

    A stable optical beat-signal with frequency GHz is produced by injection-locking two narrow-linewidth semiconductor lasers emitting at frequencies spaced by the beat-frequency to a low-jitter 10-GHz optical comb. The generated beat-signal with broadband noise suppression of dB is temporally compressed by factors of up to four in a high stimulated Brillouin scattering threshold aluminosilicate highly nonlinear fiber. The generated subpicosecond pulses have a root mean square (rms) timing jitter below 150 fs measured over 1 s.
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  • Optical grooming switch with regenerative functionality for transparent interconnection of networks

    Vorreau, P.   Sygletos, S.   Parmigiani, F.   Hillerkuss, D.   Bonk, R.   Petropoulos, P.   Richardson, D.J.   Zarris, G.   Simeonidou, D.   Klonidis, D.   Tomkos   Weerasuriya, R.   Ibrahim, S.   Ellis, A.D.   Cotter, D.   Morais, R.   Monteiro, P.   Ben Ezra, S.   Tsadka, S.   Freude, W.   Leuthold, J.  

    We demonstrate a regenerative optical grooming switch for buffer-less interconnection of metro/access and metro/core ring networks with switching functionality in time, space and wavelength domain. Key functionalities of the router are the traffic aggregation with time-slot interchanging (TSI) functionality, the WDM-to-ODTM multiplexing and the OTDM-to-WDM demultiplexing of high-speed channel into lower bitrate tributaries as well as multi-wavelength all-optical 2R regeneration of several higher-speed signals. BER and Q-factor measurements of different switching scenarios show excellent performance with no error floor and Qfactors above 21 dB.
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  • On the role of athermal electrons in non-linear photoemission from Ag(100) RID G-2395-2010

    Giannetti, C.   Ferrini, G.   Pagliara, S.   Galimberti, G.   Banfi, F.   Pedersoli, E.   Parmigiani, F.  

    The non-linear photoelectron spectra obtained by short laser pulses from a Ag(100) surface show a high-energy electron emission due to an athermal electron distribution created by the laser pulse. By comparing the photoemission at normal and non-normal emission geometry it is possible to evidence the independence of the hot electron photoemission on the parallel momentum and on different final-state configurations. A photoemission correlation measurement evidences that non-photoelectric effects, as tunneling or thermally assisted photoemission, do not contribute to the electron yield. Various theoretical models are discussed on the basis of the present data.
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  • Optical interconnection of core and metro networks RID C-9253-2011 RID D-5528-2009 RID C-7539-2009

    Ellis, A. D.   Cotter, D.   Ibrahim, S.   Weerasuriya, R.   Chow, C. W.   Leuthold, J.   Freude, W.   Sygletos, S.   Vorreau, P.   Bonk, R.   Hillerkuss, D.   Tomkos, I.   Tzanakaki, A.   Kouloumentas, C.   Richardson, D. J.   Petropoulos, P.   Parmigiani, F.   Zarris, G.   Simeonidou, D.  

    A network concept is introduced that exploits transparent optical grooming of traffic between an access network and a metro core ring network. This network is enabled by an optical router that allows bufferless aggregation of metro network traffic into higher-capacity data streams for core network transmission. A key functionality of the router is WDM to time-division multiplexing (TDM) transmultiplexing. (C) 2008 Optical Society of America
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  • An Efficient Wavelength Converter Exploiting a Grating-Based Saw-Tooth Pulse Shaper RID C-7539-2009

    Parmigiani, F.   Ibsen, M.   Ng, T. T.   Provost, L.   Petropoulos, P.   Richardson, D. J.  

    We experimentally demonstrate the generation of picosecond triangular optical pulses using a superstructured fiber Bragg grating and show experimentally that use of this pulse shape can provide a three-fold improvement in conversion efficiency relative to the use of Gaussian pulses with similar pulsewidths when used in a wavelength conversion scheme based on self-phase modulation and subsequent offset filtering.
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