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Träfflista för sökning "WFRF:(Witting Larsen Esben) "

Sökning: WFRF:(Witting Larsen Esben)

  • Resultat 1-16 av 16
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1.
  • Bengtsson, Samuel N., et al. (författare)
  • Free induction decay in the extreme ultraviolet
  • 2015
  • Ingår i: Proceedings of Frontiers in Optics 2015, FIO 2015. - 9781943580033
  • Konferensbidrag (refereegranskat)abstract
    • We present an experimental study of controlled Free Induction Decay (FID) in the extreme ultraviolet regime excited by High-order Harmonics. The control is done by applying a delayed infrared pulse.
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2.
  • Bengtsson, S., et al. (författare)
  • Space–time control of free induction decay in the extreme ultraviolet
  • 2017
  • Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 11:4, s. 252-258
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultrafast extreme-ultraviolet (XUV) and X-ray sources are revolutionizing our ability to follow femtosecond processes with ångström-scale resolution. The next frontier is to simultaneously control the direction, duration and timing of such radiation. Here, we demonstrate a fully functional opto-optical modulator for XUV light, similar to modulators available at infrared (IR) and visible wavelengths. It works by using an IR pulse to control the spatial and spectral phase of the free induction decay that results from using attosecond pulses to excite a gas. The modulator allows us to send the XUV light in a direction of our choosing at a time of our choosing. The inherent synchronization of the XUV emission to the control pulse will allow laser-pump/X-ray probe experiments with sub-femtosecond time resolution.
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3.
  • Carlström, Stefanos, et al. (författare)
  • Spatially and spectrally resolved quantum path interference with chirped driving pulses
  • 2016
  • Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18:12
  • Tidskriftsartikel (refereegranskat)abstract
    • We measure spectrally and spatially resolved high-order harmonics generated in argon using chirped multi-cycle laser pulses. Using a stable, high-repetition rate laser we observe detailed interference structures in the far-field. The structures are of two kinds; off-axis interference from the long trajectory only and on-axis interference including the short and long trajectories. The former is readily visible in the far-field spectrum, modulating both the spectral and spatial profile. To access the latter, we vary the chirp of the fundamental, imparting different phases on the different trajectories, thereby changing their relative phase. Using this method together with an analytical model, we are able to explain the on-axis behaviour and access the dipole phase parameters for the short (${\alpha }_{{\rm{s}}}$) and long (${\alpha }_{{\rm{l}}}$) trajectories. The extracted results compare very well with phase parameters calculated by solving the time-dependent Schrödinger equation. Going beyond the analytical model, we are also able to successfully reproduce the off-axis interference structure.
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4.
  • Guenot, Diego, et al. (författare)
  • Measurements of relative photoemission time delays in noble gas atoms
  • 2014
  • Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 47:24, s. 245602-
  • Tidskriftsartikel (refereegranskat)abstract
    • We determine relative photoemission time delays between valence electrons in different noble gas atoms (Ar, Ne and He) in an energy range between 31 and 37 eV. The atoms are ionized by an attosecond pulse train synchronized with an infrared laser field and the delays are measured using an interferometric technique. We compare our results with calculations using the random phase approximation with exchange and multi-configurational Hartree-Fock. We also investigate the influence of the different ionization angular channels.
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5.
  • Harth, A., et al. (författare)
  • Few-cycle high-repetition rate OPCPA for multiphoton PEEM towards atto-PEEM
  • 2016
  • Ingår i: International Conference on Ultrafast Phenomena, UP 2016. - 9781943580187 ; Part F20-UP 2016
  • Konferensbidrag (refereegranskat)abstract
    • We present a few-cycle high-repetition rate optical parametric amplifier for multiphoton PEEM experiments on semiconductor nanowires. This parametric amplifier is also used for the generation of high-order harmonics at 200kHz for future atto-PEEM experiments.
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7.
  • Ibrakovic, Neven, et al. (författare)
  • Achromatic dual-waveplate for inline two color high-order harmonic generation
  • 2018
  • Ingår i: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060. ; 72:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract: We propose a design of an achromatic dual-waveplate intended to align the polarization of orthogonal two-color pulses in an inline configuration. The waveplate acts as a half-waveplate for pulses with a carrier wavelength of 1300 nm over a bandwidth of 300 nm. For the second harmonic of the pulses the waveplate acts as a full-waveplate, centered at 650 nm with a bandwidth of 100 nm. By experimentally measuring the transmission of this optic when placed between two parallel linear polarizers we show that the polarization directions are aligned as expected. This experiment is then verified by calculating the transmission through the optic using Jones calculus. This waveplate could be useful in two-color experiments with few-cycle pulses, or pulses with a tunable wavelength, that need to be aligned with their second harmonics. Graphical abstract: [Figure not available: see fulltext.].
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8.
  • Jimenez-Galan, A., et al. (författare)
  • Phase Measurement of a Fano Resonance Using Tunable Attosecond Pulses
  • 2015
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635, s. 092137-092137
  • Konferensbidrag (refereegranskat)abstract
    • We study photoionization of argon atoms close to the 3s(2)3p(6) -> 3s(1)3p(6)4p Fano resonance using an attosecond pulse train and a weak infrared probe field. An interferometric technique combined with tunable attosecond pulses allows us to determine the phase of the photoionization amplitude as a function of photon energy. We interpret the experimental results using an analytical two-photon model based on the Fano formalism and obtain quantitative agreement.
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9.
  • Kotur, Marija, et al. (författare)
  • Spectral phase measurement of a Fano resonance using tunable attosecond pulses
  • 2016
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron dynamics induced by resonant absorption of light is of fundamental importance in nature and has been the subject of countless studies in many scientific areas. Above the ionization threshold of atomic or molecular systems, the presence of discrete states leads to autoionization, which is an interference between two quantum paths: direct ionization and excitation of the discrete state coupled to the continuum. Traditionally studied with synchrotron radiation, the probability for autoionization exhibits a universal Fano intensity profile as a function of excitation energy. However, without additional phase information, the full temporal dynamics cannot be recovered. Here we use tunable attosecond pulses combined with weak infrared radiation in an interferometric setup to measure not only the intensity but also the phase variation of the photoionization amplitude across an autoionization resonance in argon. The phase variation can be used as a fingerprint of the interactions between the discrete state and the ionization continua, indicating a new route towards monitoring electron correlations in time.
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10.
  • Kroon, David, et al. (författare)
  • Attosecond pulse walk-off in high-order harmonic generation
  • 2014
  • Ingår i: Optics Letters. - 0146-9592. ; 39:7, s. 2218-2221
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the influence of the generation conditions on the group delay of attosecond pulses in high-order harmonic generation in gases. The group delay relative to the fundamental field is found to decrease with increasing gas pressure in the generation cell, reflecting a temporal walk-off due to the dispersive properties of the nonlinear medium. This effect is well reproduced using an on-axis phase-matching model of high-order harmonic generation in an absorbing gas. (C) 2014 Optical Society of America
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11.
  • Larsen, Esben Witting, et al. (författare)
  • Sub-cycle ionization dynamics revealed by trajectory resolved, elliptically-driven high-order harmonic generation
  • 2016
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
  • Tidskriftsartikel (refereegranskat)abstract
    • The sub-cycle dynamics of electrons driven by strong laser fields is central to the emerging field of attosecond science. We demonstrate how the dynamics can be probed through high-order harmonic generation, where different trajectories leading to the same harmonic order are initiated at different times, thereby probing different field strengths. We find large differences between the trajectories with respect to both their sensitivity to driving field ellipticity and resonant enhancement. To accurately describe the ellipticity dependence of the long trajectory harmonics we must include a sub-cycle change of the initial velocity distribution of the electron and its excursion time. The resonant enhancement is observed only for the long trajectory contribution of a particular harmonic when a window resonance in argon, which is off-resonant in the field-free case, is shifted into resonance due to a large dynamic Stark shift.
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12.
  • Lorek, Eleonora, et al. (författare)
  • High-order harmonic generation using a high-repetition-rate turnkey laser.
  • 2014
  • Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 85:12
  • Tidskriftsartikel (refereegranskat)abstract
    • We generate high-order harmonics at high pulse repetition rates using a turnkey laser. High-order harmonics at 400 kHz are observed when argon is used as target gas. In neon, we achieve generation of photons with energies exceeding 90 eV (∼13 nm) at 20 kHz. We measure a photon flux of up to 4.4 × 10(10) photons per second per harmonic in argon at 100 kHz. Many experiments employing high-order harmonics would benefit from higher repetition rates, and the user-friendly operation opens up for applications of coherent extreme ultra-violet pulses in new research areas.
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13.
  • Louisy, Maite, et al. (författare)
  • Gating attosecond pulses in a noncollinear geometry
  • 2015
  • Ingår i: Optica. - 2334-2536. ; 2:6, s. 563-566
  • Tidskriftsartikel (refereegranskat)abstract
    • The efficient generation of isolated attosecond pulses (IAPs), giving access to ultrafast electron dynamics in various systems, is a key challenge in attosecond science. IAPs can be produced by confining the extreme ultraviolet emission generated by an intense laser pulse to a single field half-cycle or, as shown recently, by employing angular streaking methods. Here, we experimentally demonstrate the angular streaking of attosecond pulse trains in a noncollinear geometry, leading to the emission of angularly separated IAPs. The noncollinear geometry simplifies the separation of the fundamental laser field and the generated pulses, making this scheme promising for intracavity attosecond pulse generation, thus opening new possibilities for high-repetition-rate attosecond sources. (C) 2015 Optical Society of America
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14.
  • Mårsell, Erik, et al. (författare)
  • Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths
  • 2015
  • Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 117:8
  • Tidskriftsartikel (refereegranskat)abstract
    • We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 mu m. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate. (C) 2015 AIP Publishing LLC.
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15.
  • Rudawski, Piotr, et al. (författare)
  • Carrier-envelope phase dependent high-order harmonic generation with a high-repetition rate OPCPA-system
  • 2015
  • Ingår i: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060. ; 69:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We study high-order harmonic generation with a high-repetition rate (200 kHz), few-cycle, driving laser, based on optical parametric chirped pulse amplification. The system delivers carrier-envelope phase stable, 8 fs, 10 mu J pulses at a central wavelength of 890 nm. High-order harmonics, generated in a high-pressure Ar gas jet, exhibit a strong CEP-dependence over a large spectral range owing to excellent stability of the driving laser pulses. This range can be divided into three spectral regions with distinct CEP influence. The observed spectral interference structures are explained by an analytical model based upon multiple pulse interferences.
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  • Resultat 1-16 av 16

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