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Sökning: WFRF:(Mauritsson J)

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1.
  • L'Huillier, A., et al. (författare)
  • Atomic physics with attosecond pulses
  • 2006
  • Ingår i: International Conference on Ultrafast Phenomena, UP 2006. - 1557528101 - 9781557528100
  • Konferensbidrag (refereegranskat)
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2.
  • Maroju, P. K., et al. (författare)
  • Analysis of two-color photoelectron spectroscopy for attosecond metrology at seeded free-electron lasers
  • 2021
  • Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The generation of attosecond pulse trains at free-electron lasers opens new opportunities in ultrafast science, as it gives access, for the first time, to reproducible, programmable, extreme ultraviolet (XUV) waveforms with high intensity. In this work, we present a detailed analysis of the theoretical model underlying the temporal characterization of the attosecond pulse trains recently generated at the free-electron laser FERMI. In particular, the validity of the approximations used for the correlated analysis of the photoelectron spectra generated in the two-color photoionization experiments are thoroughly discussed. The ranges of validity of the assumptions, in connection with the main experimental parameters, are derived.
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3.
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4.
  • Makos, I., et al. (författare)
  • Attosecond photoelectron spectroscopy using high-harmonic generation and seeded free-electron lasers
  • 2023
  • Ingår i: 2023 Photonics North, PN 2023. - 9798350326734
  • Konferensbidrag (refereegranskat)abstract
    • In this work, we use attosecond time-resolved techniques to investigate photoionization dynamics on its natural timescale, employing both high harmonic generation and seeded free-electron lasers to generate extreme ultraviolet attosecond pulse trains for our studies. With the former approach, we examine the role of nuclear motion in molecular photoionization dynamics, while with the latter we introduce a novel attosecond timing tool for single-shot characterization of the relative phase between the XUV and the infrared field.
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5.
  • Sansone, G., et al. (författare)
  • Attosecond excitation of electron wavepackets
  • 2008
  • Ingår i: Quantum Electronics and Laser Science Conference, QELS 2008. - 9781557528599
  • Konferensbidrag (refereegranskat)abstract
    • We present experiments, supported by time-dependent Schrödinger simulations, on the dynamics of Helium bound states after an attosecond excitation in the presence of a strong infrared laser field.
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6.
  • Varju, Katalin, et al. (författare)
  • Angularly resolved electron wave packet interferences
  • 2006
  • Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:18, s. 3983-3991
  • Tidskriftsartikel (refereegranskat)abstract
    • We study experimentally the ionization of argon atoms by a train of attosecond pulses in the presence of a strong infrared laser field, using a velocity map imaging technique. The recorded momentum distribution strongly depends on the delay between the attosecond pulses and the laser field. We interpret the interference patterns observed for different delays using numerical and analytical calculations within the strong field approximation.
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7.
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8.
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9.
  • Klünder, Kathrin, et al. (författare)
  • Reconstruction of attosecond electron wave packets using quantum state holography
  • 2013
  • Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 88:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a method for performing quantum state holography, with which we completely characterize the amplitude and phase of an attosecond electron wave packet. Our approach is an extension of a recent publication [J. Mauritsson et al., Phys. Rev. Lett. 105, 053001 (2010)] in which we demonstrated experimentally that the energies and amplitudes of an attosecond electron wave packet can be characterized using attosecond electron interferometry. Here we show theoretically that attosecond electron interferometry can be extended to retrieve the phases of all the states that make up the wave packet. We demonstrate the feasibility of our method by analyzing a wave packet created by a shake-up process. We show that our method can successfully retrieve arbitrary phases and/or lifetimes added to the component eigenstates.
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10.
  • Maroju, Praveen Kumar, et al. (författare)
  • Attosecond coherent control of electronic wave packets in two-colour photoionization using a novel timing tool for seeded free-electron laser
  • 2023
  • Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 17, s. 200-207
  • Tidskriftsartikel (refereegranskat)abstract
    • In ultrafast spectroscopy, the temporal resolution of time-resolved experiments depends on the duration of the pump and probe pulses, and on the control and characterization of their relative synchronization. Free-electron lasers operating in the extreme ultraviolet and X-ray spectral regions deliver pulses with femtosecond and attosecond duration in a broad array of pump-probe configurations to study a wide range of physical processes. However, this flexibility, together with the large dimensions and high complexity of the experimental set-ups, limits control of the temporal delay to the femtosecond domain, thus precluding a time resolution below the optical cycle. Here we demonstrate a novel single-shot technique able to determine the relative synchronization between an attosecond pulse train-generated by a seeded free-electron laser-and the optical oscillations of a near-infrared field, with a resolution of one atomic unit (24 as). Using this attosecond timing tool, we report the first example of attosecond coherent control of photoionization in a two-colour field by manipulating the phase of high-order near-infrared transitions.
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11.
  • Mauritsson, Johan, et al. (författare)
  • Attosecond Electron Spectroscopy Using a Novel Interferometric Pump-Probe Technique
  • 2010
  • Ingår i: Physical Review Letters. - 1079-7114. ; 105:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an interferometric pump-probe technique for the characterization of attosecond electron wave packets (WPs) that uses a free WP as a reference to measure a bound WP. We demonstrate our method by exciting helium atoms using an attosecond pulse (AP) with a bandwidth centered near the ionization threshold, thus creating both a bound and a free WP simultaneously. After a variable delay, the bound WP is ionized by a few-cycle infrared laser precisely synchronized to the original AP. By measuring the delay-dependent photoelectron spectrum we obtain an interferogram that contains both quantum beats as well as multipath interference. Analysis of the interferogram allows us to determine the bound WP components with a spectral resolution much better than the inverse of the AP duration.
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12.
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13.
  • 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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14.
  • Carré, B., et al. (författare)
  • Characterization of attosecond pulse trains
  • 2007
  • Ingår i: Ultrafast Optics V. - New York, NY : Springer New York. - 1556-1534 .- 0342-4111. - 9780387491172 ; 132, s. 45-56
  • Konferensbidrag (refereegranskat)abstract
    • Ultrashort light pulses, as short as 100 as, can be produced from high harmonic generation (HHG) in an atomic gas medium. This major achievement of the last 6 years in high field physics has now been demonstrated in different conditions of medium-field interaction [1].
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15.
  • Gisselbrecht, M., et al. (författare)
  • Attosecond insight into electron correlation
  • 2019
  • Ingår i: Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015. - 9781467374750
  • Konferensbidrag (refereegranskat)abstract
    • Photoionization with a single photon is one of the fundamental processes in nature, in which one electron is ripped away from its atom. Traditionally studied in the energy domain, this process was believed to be instantaneous, but recent advances in the production of attosecond pulses (1 as 10−18 s) in the eXtreme UltraViolet (XUV) have renewed interest in understanding the temporal aspects of electron emission in atoms, molecules and the solid state [1–8]. We present here our progress in understanding the influence of electronic correlations on the attosecond photoionization dynamics.
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16.
  • Guenot, Diego, et al. (författare)
  • Probing electron correlation on the attosecond time scale
  • 2014
  • Ingår i: High Intensity Lasers and High Field Phenomena, HILAS 2014. - 9781557529954
  • Konferensbidrag (refereegranskat)abstract
    • We present experimental measurements and theoretical calculations of single and double ionization time delays in various noble gases using an interferometric method. The measured delays allow us to extract information on the electron correlation.
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17.
  • 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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18.
  • Johnsson, Per, et al. (författare)
  • Attosecond electron wave packet dynamics in strong laser fields
  • 2005
  • Ingår i: Physical Review Letters. - 1079-7114. ; 95:1, s. 1-013001
  • Tidskriftsartikel (refereegranskat)abstract
    • We use a train of sub-200 attosecond extreme ultraviolet (XUV) pulses with energies just above the ionization threshold in argon to create a train of temporally localized electron wave packets. We study the energy transfer from a strong infrared (IR) laser field to the ionized electrons as a function of the delay between the XUV and IR fields. When the wave packets are born at the zero crossings of the IR field, a significant amount of energy (similar to 20 eV) is transferred from the field to the electrons. This results in dramatically enhanced above-threshold ionization in conditions where the IR field alone does not induce any significant ionization. Because both the energy and duration of the wave packets can be varied independently of the IR laser, they are valuable tools for studying and controlling strong-field processes.
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19.
  • Kumar Maroju, Praveen, et al. (författare)
  • Attosecond pulse shaping using a seeded free-electron laser
  • 2020
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 578, s. 386-391
  • Tidskriftsartikel (refereegranskat)abstract
    • Attosecond pulses are central to the investigation of valence- and core-electron dynamics on their natural timescales. The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high-order harmonic generation. Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters, multilayer mirrors and manipulation of the driving field. However, none of these approaches allows the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high-order harmonic generation process. Free-electron lasers, by contrast, deliver femtosecond, extreme-ultraviolet and X-ray pulses with energies ranging from tens of microjoules to a few millijoules. Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot-to-shot. Here we report reproducible generation of high-energy (microjoule level) attosecond waveforms using a seeded free-electron laser. We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with an approach for its temporal reconstruction. The results presented here open the way to performing attosecond time-resolved experiments with free-electron lasers.
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20.
  • Lopez, Rodrigo, et al. (författare)
  • Amplitude and phase control of attosecond light pulses
  • 2005
  • Ingår i: Physical Review Letters. - 1079-7114. ; 94:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the generation, compression, and delivery on target of ultrashort extreme-ultraviolet light pulses using external amplitude and phase control. Broadband harmonic radiation is first generated by focusing an infrared laser with a carefully chosen intensity into a gas cell containing argon atoms. The emitted light then goes through a hard aperture and a thin aluminum filter that selects a 30-eV bandwidth around a 30-eV photon energy and synchronizes all of the components, thereby enabling the formation of a train of almost Fourier-transform-limited single-cycle 170 attosecond pulses. Our experiment demonstrates a practical method for synthesizing and controlling attosecond waveforms.
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21.
  • Maroju, Praveen K., et al. (författare)
  • A Novel Attosecond Timing Tool for Free-Electron Laser Experiment
  • 2020
  • Ingår i: High Intensity Lasers and High Field Phenomena 2020. - 9781943580736
  • Konferensbidrag (refereegranskat)abstract
    • We demonstrate a novel timing tool for Free-Electron Lasers to determine the delay between an attosecond pulse train and infrared pulse with sub-optical-cycle resolu-. tion.
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22.
  • Maroju, Praveen Kumar, et al. (författare)
  • Complex attosecond waveform synthesis at fel fermi
  • 2021
  • Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 11:21
  • Tidskriftsartikel (refereegranskat)abstract
    • Free-electron lasers (FELs) can produce radiation in the short wavelength range extending from the extreme ultraviolet (XUV) to the X-rays with a few to a few tens of femtoseconds pulse duration. These facilities have enabled significant breakthroughs in the field of atomic, molecular, and optical physics, implementing different schemes based on two-color photoionization mechanisms. In this article, we present the generation of attosecond pulse trains (APTs) at the seeded FEL FERMI using the beating of multiple phase-locked harmonics. We demonstrate the complex attosecond waveform shaping of the generated APTs, exploiting the ability to manipulate independently the amplitudes and the phases of the harmonics. The described generalized attosecond waveform synthesis technique with an arbitrary number of phase-locked harmonics will allow the generation of sub-100 as pulses with programmable electric fields.
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23.
  • Olofsson, A., et al. (författare)
  • Opto-optical modulator (OOM) for extreme ultraviolet pulses
  • 2020. - 7
  • Ingår i: Attosecond Physics. - : IOP Publishing. - 1742-6588. ; 1412
  • Konferensbidrag (refereegranskat)abstract
    • There is a profound, almost symbiotic relation between electrons and photons. When light interacts with matter the electrons in the material will start to move and oscillate. When a charged particle, such as an electron, oscillates it will act as a dipole and emit light. We utilize this symbiotic relation and extend the control of light to the extreme ultraviolet (XUV) region using the newly developed XUV opto-optical modulator.
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24.
  • Petersson, C. L M, et al. (författare)
  • Phase metrology with multi-cycle two-colour pulses
  • 2016
  • Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 49:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Strong-field phenomena driven by an intense infrared (IR) laser depend on during what part of the field cycle they are initiated. By changing the sub-cycle character of the laser electric field it is possible to control such phenomena. For long pulses, sub-cycle shaping of the field can be done by adding a relatively weak, second harmonic of the driving field to the pulse. Through constructive and destructive interference, the combination of strong and weak fields can be used to change the probability of a strong-field process being initiated at any given part of the cycle. In order to control sub-cycle phenomena with optimal accuracy, it is necessary to know the phase difference of the strong and the weak fields precisely. If the weaker field is an even harmonic of the driving field, electrons ionized by the field will be asymmetrically distributed between the positive and negative directions of the combined fields. Information about the asymmetry can yield information about the phase difference. A technique to measure asymmetry for few-cycle pulses, called stereo-ATI (above threshold ionization), has been developed by Paulus et al (2003 Phys. Rev. Lett. 91 253004). This paper outlines an extension of this method to measure the phase difference between a strong IR and its second harmonic.
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25.
  • Remetter, Thomas, et al. (författare)
  • Attosecond electron wave packet interferometry
  • 2006
  • Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 2:5, s. 323-326
  • Tidskriftsartikel (refereegranskat)abstract
    • A complete quantum-mechanical description of matter and its interaction with the environment requires detailed knowledge of a number of complex parameters. In particular, information about the phase of wavefunctions is important for predicting the behaviour of atoms, molecules or larger systems. In optics, information about the evolution of the phase of light in time(1) and space(2) is obtained by interferometry. To obtain similar information for atoms and molecules, it is vital to develop analogous techniques. Here we present an interferometric method for determining the phase variation of electronic wave packets in momentum space, and demonstrate its applicability to the fundamental process of single-photon ionization. We use a sequence of extreme-ultraviolet attosecond pulses(3,4) to ionize argon atoms and an infrared laser field, which induces a momentum shear(5) between consecutive electron wave packets. The interferograms that result from the interaction of these wave packets provide useful information about their phase. This technique opens a promising new avenue for reconstructing the wavefunctions(6,7) of atoms and molecules and for following the ultrafast dynamics of electronic wave packets.
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26.
  • Simpson, E. R., et al. (författare)
  • Probing Stark-induced nonlinear phase variation with opto-optical modulation
  • 2019
  • Ingår i: Physical Review A. - 2469-9926. ; 100:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We extend the recently developed technique of opto-optical modulation (OOM) to probe state-resolved ac-Stark-induced phase variations of a coherently excited ensemble of helium atoms. In a joint experimental and theoretical study, we find that the spatial redirection of the resonant emission from the OOM process is different for the low-lying 1s2p state as compared with the higher-lying Rydberg states, and that this redirection can be controlled through the spatial characteristics of the infrared (IR) probe beam. In particular, we observe that the intensity dependence of the IR-induced Stark phase on the 1s2p emission is nonlinear, and that the phase accumulation changes sign for moderate intensities. Our results suggest that OOM, combined with precise experimental shaping of the probe beam, could allow future measurements of Stark-induced phase shifts of excited states.
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27.
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28.
  • Tcherbakoff, O., et al. (författare)
  • Controlling the duration of XUV high order harmonic pulses
  • 2003
  • Ingår i: 2003 Conference on Lasers and Electro-Optics Europe, CLEO/EUROPE 2003. - 0780377346 - 9780780377349
  • Konferensbidrag (refereegranskat)abstract
    • We modulate temporally the polarization of a ∼ 30 fs, 800 nm IR pulse and use it to generate high order harmonics. The harmonic emission can clearly be confined and the XUV pulse duration can be continuously tuned from - 5 - 7 fs to 50 fs.
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29.
  • Zaïr, A., et al. (författare)
  • Confinement of attosecond train pulses by using a modulated polarization IR pulse
  • 2005
  • Ingår i: 2005 Conference on Lasers and Electro-Optics Europe. - 0780389743 - 9780780389748
  • Konferensbidrag (refereegranskat)abstract
    • We study the temporal and spectral behaviour of high order harmonics generated by pulses with temporally modulated polarization. We observe a harmonic temporal confinement and a harmonic spectral broadening, compatible with 1 -or-2 attosecond pulse emission.
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30.
  • Arnold, C. L., et al. (författare)
  • Stabilized interferometric attosecond timing measurements
  • 2013
  • Ingår i: CLEO : QELS_Fundamental Science, CLEO:QELS FS 2013 - QELS_Fundamental Science, CLEO:QELS FS 2013. - 9781557529725
  • Konferensbidrag (refereegranskat)abstract
    • We perform interferometric attosecond timing measurements to study XUV photoionization in noble gases, to diagnose macroscopic phase-matching conditions in high-order harmonic generation, and to investigate single-photon double-ionization by detecting electron pairs in coincidence.
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31.
  • Bengtsson, S., et al. (författare)
  • Experimental observation of longer trajectories than previously observed in high-order harmonic generation
  • 2023
  • Ingår i: Physical Review A. - 2469-9926. ; 108:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We experimentally observe longer than long trajectory influence in high-order harmonic generation (HHG) by varying the peak intensity of the driving laser field either through direct attenuation or by chirping the laser pulse. Using a theoretical Gaussian beam model to simulate spatial interference resulting from quantum path interference, we show that the measured interference patterns cannot be solely explained by the well-established short and long trajectories. The structure change is most prominent for the more divergent, off-axis components of the lower plateau harmonic region, affecting the direction and amplitude of the extreme ultraviolet light emitted, and is thus of importance for understanding and controlling the fundamentals of the HHG process.
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32.
  • Biegert, Jens, et al. (författare)
  • Control of the frequency chirp rate of high harmonic pulses
  • 2004
  • Ingår i: Springer Series in Chemical Physics. - 0172-6218. ; 79, s. 204-206
  • Tidskriftsartikel (refereegranskat)abstract
    • We measured the frequency chirp rate of harmonics 13 to 23 in argon by cross-correlation with a short femtosecond probe pulse. We directly measured the negative chirp due to the atomic dipole phase and demonstrated that an additional chirp on the pump pulse was transferred to the qth harmonic as q times the fundamental chirp.
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33.
  • Brizuela, Fernando, et al. (författare)
  • Efficient high order harmonic generation boosted by below threshold harmonics
  • 2013
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3
  • Tidskriftsartikel (refereegranskat)abstract
    • High-order harmonic generation (HHG) in gases has been established as an important technique for the generation of coherent extreme ultraviolet (XUV) pulses at ultrashort time scales. Its main drawback, however, is the low conversion efficiency, setting limits for many applications, such as ultrafast coherent imaging, nonlinear processes in the XUV range, or seeded free electron lasers. Here we introduce a novel scheme based on using below-threshold harmonics, generated in a seeding cell, to boost the HHG process in a generation cell, placed further downstream in the focused laser beam. By modifying the fundamental driving field, these low-order harmonics alter the ionization step of the nonlinear HHG process. Our dual-cell scheme enhances the conversion efficiency of HHG, opening the path for the realization of robust intense attosecond XUV sources.
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34.
  • Carlström, Stefanos, et al. (författare)
  • Quantum coherence in photo-ionisation with tailored XUV pulses
  • 2018
  • Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 51:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Ionisation with ultrashort pulses in the extreme ultraviolet (XUV) regime can be used to prepare an ion in a superposition of spin-orbit substates. In this work, we study the coherence properties of such a superposition, created by ionising xenon atoms using two phase-locked XUV pulses at different frequencies. In general, if the duration of the driving pulse exceeds the quantum beat period, dephasing will occur. If however, the frequency difference of the two pulses matches the spin-orbit splitting, the coherence can be efficiently increased and dephasing does not occur.
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35.
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36.
  • Dahlström, J. Marcus, 1982-, et al. (författare)
  • Theory of attosecond delays in laser-assisted photoionization
  • 2013
  • Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 414, s. 53-64
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the temporal aspects of laser-assisted extreme ultraviolet (XUV) photoionization using attosecond pulses of harmonic radiation. The aim of this paper is to establish the general form of the phase of the relevant transition amplitudes and to make the connection with the time-delays that have been recently measured in experiments. We find that the overall phase contains two distinct types of contributions: one is expressed in terms of the phase-shifts of the photoelectron continuum wavefunction while the other is linked to continuum–continuum transitions induced by the infrared (IR) laser probe. Our formalism applies to both kinds of measurements reported so far, namely the ones using attosecond pulse trains of XUV harmonics and the others based on the use of isolated attosecond pulses (streaking). The connection between the phases and the time-delays is established with the help of finite difference approximations to the energy derivatives of the phases. The observed time-delay is a sum of two components: a one-photon Wigner-like delay and an universal delay that originates from the probing process itself.
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37.
  • Gisselbrecht, Mathieu, et al. (författare)
  • Exploring single-photon ionization on the attosecond time scale
  • 2012
  • Ingår i: XXVII International Conference on Photonic, Electronic and Atomic Collisions (Icpeac 2011), Pts 1-15. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388, s. 032025-032025
  • Konferensbidrag (refereegranskat)abstract
    • One of the fundamental processes in nature is the photoelectric effect in which an electron is ripped away from its atom via the interaction with a photon. This process was long believed to be instantaneous but with the development of attosecond pulses (1 as 10(-18) s) we can finally get an insight into its dynamic. Here we measure a delay in ionization time between two differently bound electrons. The outgoing electrons are created via ionization with a train of attosecond pulses and we probe their relative delay with a synchronized infrared laser. We demonstrate how this probe field influences the measured delays and show that this contribution can be estimated with a universal formula, which allows us to extract field free atomic data..
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38.
  • 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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39.
  • Guenot, Diego, et al. (författare)
  • Photoemission time delay measurements and calculations close to the 3s ionization cross section minimum in ar
  • 2012
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 85:5, s. 053424-
  • Tidskriftsartikel (refereegranskat)abstract
    • We present experimental measurements and theoretical calculations of photoionization time delays from the 3s and 3p shells in Ar in the photon energy range of 32-42 eV. The experimental measurements are performed by interferometry using attosecond pulse trains and the infrared laser used for their generation. The theoretical approach includes intershell correlation effects between the 3s and 3p shells within the framework of the random-phase approximation with exchange. The connection between single-photon ionization and the two-color two-photon ionization process used in the measurement is established using the recently developed asymptotic approximation for the complex transition amplitudes of laser-assisted photoionization. We compare and discuss the theoretical and experimental results, especially in the region where strong intershell correlations in the 3s -> kp channel lead to an induced Cooper minimum in the 3s ionization cross section.
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40.
  • Guo, Chen, et al. (författare)
  • Phase control of attosecond pulses in a train
  • 2018
  • Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 51:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultrafast processes in matter can be captured and even controlled by using sequences of few-cycle optical pulses, which need to be well characterized, both in amplitude and phase. The same degree of control has not yet been achieved for few-cycle extreme ultraviolet pulses generated by high-order harmonic generation (HHG) in gases, with duration in the attosecond range. Here, we show that by varying the spectral phase and carrier-envelope phase (CEP) of a high-repetition rate laser, using dispersion in glass, we achieve a high degree of control of the relative phase and CEP between consecutive attosecond pulses. The experimental results are supported by a detailed theoretical analysis based upon the semi-classical three-step model for HHG.
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41.
  • Heyl, C. M., et al. (författare)
  • Noncollinear optical gating - A method for intra-cavity single attosecond pulse generation?
  • 2019
  • Ingår i: Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015. - 9781467374750
  • Konferensbidrag (refereegranskat)abstract
    • The process of high-order harmonic generation requires laser intensities around 1014 W/cm2, most easily reached with laser pulses of high energy, thus implicitly limiting the repetition rate of attosecond sources. A route towards multi-MHz attosecond sources relies on HHG inside a passive enhancement cavity [1]. Although successfully demonstrated for attosecond pulse trains, the generation of single attosecond pulses (SAPs) inside a cavity remains an unsolved challenge, mainly limited by dispersion management and out-coupling problems. We recently proposed a new gating concept for SAP generation [2], noncollinear optical gating (NOG) which has the potential to facilitate SAP gating and efficient out-coupling at once. Similar to the recently introduced attosecond lighthouse [3] NOG employs attosecond angular streaking [4] and combines this concept with noncollinear HHG, proposed earlier [5] as out-coupling method for intra cavity HHG.
  •  
42.
  • 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.
  •  
43.
  • Johnsson, Per, et al. (författare)
  • Attosecond control of ionization by wave-packet interference
  • 2007
  • Ingår i: Physical Review Letters. - 1079-7114. ; 99:23
  • Tidskriftsartikel (refereegranskat)abstract
    • A train of attosecond pulses, synchronized to an infrared (IR) laser field, is used to create a series of electron wave packets (EWPs) that are below the ionization threshold in .helium. The ionization probability is found to strongly oscillate with the delay between the IR and attosecond fields twice per IR laser cycle. Calculations that reproduce the experimental results demonstrate that this ionization control results from interference between transiently bound EWPs created by different pulses in the train. In this way, we are able to observe, for the first time, attosecond wave-packet interference in a strongly driven atomic system.
  •  
44.
  • Johnsson, Per, et al. (författare)
  • Trains of attosecond electron wave packets
  • 2006
  • Ingår i: Journal of Modern Optics. - : Informa UK Limited. - 0950-0340 .- 1362-3044. ; 53:1-2, s. 233-245
  • Tidskriftsartikel (refereegranskat)abstract
    • We study temporally localized electron wave packets, generated using a train of extreme ultraviolet (XUV) attosecond pulses to ionize the target atoms. Both the electron wave packets and the attosecond pulse train ( APT) are characterized using the same technique, based on interference of two-photon transitions in the continuum. We study, in particular, the energy transfer from a moderately strong infrared (IR) field to the electron wave packets as a function of time delay between the XUV and the IR fields. The use of an APT to generate the electron wave packets enables the generation at times not accessible through tunneling ionization. We find that a significant amount of energy is transferred from the IR field to the electron wave packets, when they are generated at a zero-crossing of the IR laser field. This energy transfer results in a dramatically enhanced above-threshold ionization even at IR intensities that alone are not strong enough to induce any significant ionization.
  •  
45.
  • Klünder, Kathrin, et al. (författare)
  • Probing Single-Photon Ionization on the Attosecond Time Scale
  • 2011
  • Ingår i: Physical Review Letters. - 1079-7114. ; 106:14
  • Tidskriftsartikel (refereegranskat)abstract
    • We study photoionization of argon atoms excited by attosecond pulses using an interferometric measurement technique. We measure the difference in time delays between electrons emitted from the 3s(2) and from the 3p(6) shell, at different excitation energies ranging from 32 to 42 eV. The determination of photoemission time delays requires taking into account the measurement process, involving the interaction with a probing infrared field. This contribution can be estimated using a universal formula and is found to account for a substantial fraction of the measured delay.
  •  
46.
  •  
47.
  • 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.
  •  
48.
  • Lopez, Rodrigo, et al. (författare)
  • Characterization of high-order harmonic radiation on femtosecond and attosecond time scales
  • 2004
  • Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 78:7-8, s. 835-840
  • Tidskriftsartikel (refereegranskat)abstract
    • We characterize the temporal structure of high-order harmonic radiation on both the femtosecond and attosecond time scales. The harmonic emission is characterized by mixed-color two-photon ionization with an infrared femtosecond laser using a Mach-Zehnder interferometer where both pump and probe arms travel completely separate paths. In a first experiment, we measure the duration and chirp of individual harmonics. In a second experiment, we resolve, for the first time with this type of setup, the attosecond beating of several harmonics generated under conditions similar to the first experiment. We suggest that the results of both measurements can be combined to determine the full attosecond time structure of the harmonic emission.
  •  
49.
  • Lorek, Eleonora, et al. (författare)
  • High-Order Harmonic Generation and Plasmonics
  • 2015
  • Ingår i: Nano-Structures for Optics and Photonics : Optical Strategies for Enhancing Sensing, Imaging, Communication and Energy Conversion - Optical Strategies for Enhancing Sensing, Imaging, Communication and Energy Conversion. - Dordrecht : Springer Netherlands. - 9789401791328 - 9789401791335 ; , s. 531-531
  • Bokkapitel (refereegranskat)abstract
    • Attosecond pulses allow for imaging of very fast processes, like electron dynamics. Stockman et al. suggested to use these pulses in connection with a Photoemission electron microscope (PEEM) to study the ultrafast dynamics of plasmons (Stockman et al. Nat Photonics 1:539–544, 2007). For efficient plasmon studies, the repetition rate of the attosecond pulses used needs to be higher than a few kHz (Mikkelsen et al. Rev Sci Instrum 80:123703, 2009). Attosecond pulses are produced in a process called high-order harmonic generation (HHG) (Paul et al. Science 292(5522):1689–1692, 2001; Ferray et al. J Phys B At Mol Opt Phys 21:L31–L35, 1988). In HHG, a strong laser field allows an electron to tunnel out, get accelerated and recombine with a high kinetic energy resulting in extreme ultraviolet attosecond pulses. The large intensity needed to drive the process normally limits the repetition rate of the laser to a few kHz. Using a tight focusing scheme (Heyl et al. Phys Rev Lett 107:033903, 2011; Vernaleken et al. Opt Lett 36:3428–3430, 2011), we, however, generate harmonics at a repetition rate of 200 kHz, both with a commercial turn-key laser and with an advanced laser system. Suitable nanostructures for a strong field enhancement are produced in-house and the field enhancement is studied with PEEM in a non-time resolved manner. With high-order harmonics produced at a high repetition rate, we hope to be able to follow also the ultrafast dynamics of plasmons in these structures (Mårsell et al. Ann der Phys 525:162–170, 2013).
  •  
50.
  • Mansten, Erik, et al. (författare)
  • Spectral signature of short attosecond pulse trains.
  • 2009
  • Ingår i: Physical Review Letters. - 1079-7114. ; 102:8
  • Tidskriftsartikel (refereegranskat)abstract
    • We report experimental measurements of high-order harmonic spectra generated in Ar using a carrier-envelope-offset (CEO) stabilized 12 fs, 800 nm laser field and a fraction (less than 10%) of its second harmonic. Additional spectral peaks are observed between the harmonic peaks, which are due to interferences between multiple pulses in the train. The position of these peaks varies with the CEO and their number is directly related to the number of pulses in the train. An analytical model, as well as numerical simulations, support our interpretation.
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