SwePub - search: WFRF:(Lhuillier M)

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51.	Laurell, H., et al. (author) Continuous-variable quantum state tomography of photoelectrons 2022 In: Physical Review Research. - 2643-1564. ; 4:3 Journal article (peer-reviewed)abstract We propose a continuous variable quantum state tomography protocol of electrons which result from the ionization of atoms or molecules by the absorption of extreme ultraviolet light pulses. Our protocol is benchmarked against a direct calculation of the quantum state of photoelectrons ejected from helium and argon in the vicinity of a Fano resonance. In the latter case, we furthermore distill ion-photoelectron entanglement due to spin-orbit splitting. This opens routes toward the investigation of quantum coherence and entanglement properties on the ultrafast timescale.
52.	Lepine, F., et al. (author) Short XUV pulses to characterize field-free molecular alignment 2007 In: Journal of Modern Optics. - : Informa UK Limited. - 0950-0340 .- 1362-3044. ; 54:7, s. 953-966 Journal article (peer-reviewed)abstract We present experiments on field-free molecular alignment of N-2 and CO2 probed with short XUV pulses that are obtained via high-harmonic generation. The XUV pulses induce a dissociative ionization or a Coulomb explosion of the molecule, where the fragment ion recoil (measured using the velocity map imaging technique) provides information on the alignment of the parent molecule at the time of ionization. We discuss how photoelectron detection may in future allow the determination of molecular-frame photoelectron angular distributions and molecular structure.
53.	L'Huillier, A., et al. (author) Atomic physics with attosecond pulses 2006 In: International Conference on Ultrafast Phenomena, UP 2006. - 1557528101 - 9781557528100 Conference paper (peer-reviewed)
54.	L'Huillier, Anne, et al. (author) High-order Harmonic-generation Cutoff 1993 In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 48:5 Journal article (peer-reviewed)abstract We have experimentally determined the harmonic-generation cutoff as a function of the laser intensity in neon using an intense, short-pulse Ti:sapphire laser. The experimental cutoff is lower than that obtained in single-atom calculations. Using a simple quantum-mechanical approach to harmonic generation valid at high intensity, we show that the difference is due to the effect of propagation.
55.	L'Huillier, Anne, et al. (author) High-order Harmonics - A Coherent Source In the Xuv Range 1995 In: Journal of Nonlinear Optical Physics & Materials. - 0218-1991. ; 4:3, s. 647-665 Journal article (peer-reviewed)abstract We review the main results concerning high-order generation processes from the point of view of a potential user of this new source of XUV radiation. The perspectives for optimizing the source, both in efficiency and in spectral range, its characteristics and in particular, its coherence properties, are discussed. Finally, we describe two experiments, which demonstrate the usefulness of the harmonics as a short-pulse, coherent source in the XUV domain.
56.	Lorek, Eleonora, et al. (author) High-Order Harmonic Generation and Plasmonics 2015 In: 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 Book chapter (peer-reviewed)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).
57.	Mansten, Erik, et al. (author) Spectral signature of short attosecond pulse trains. 2009 In: Physical Review Letters. - 1079-7114. ; 102:8 Journal article (peer-reviewed)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.
58.	Miranda, M., et al. (author) Generation and spatiotemporal characterization of ultrashort vortex pulses 2019 In: Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015. - 9781467374750 Conference paper (peer-reviewed)abstract Some light beams rotate as they propagate. If it is not the polarization vector, but the phase structure that rotates, the beam is said to carry orbital angular momentum (OAM). Such beams exhibit a helical phase front, where the phase rotates around a symmetry center. Because the phase in the center is undefined (and the intensity there is therefore zero), it is often termed a phase singularity or optical vortex by analogy to superfluidic vortices. Vortex beams [1,2] and more specifically ultrashort (few cycle) vortex pulses [3] have recently attracted strong interest.
59.	Nandi, S., et al. (author) Attosecond timing of electron emission from a molecular shape resonance 2020 In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 6:31 Journal article (peer-reviewed)abstract Shape resonances in physics and chemistry arise from the spatial confinement of a particle by a potential barrier. In molecular photoionization, these barriers prevent the electron from escaping instantaneously, so that nuclei may move and modify the potential, thereby affecting the ionization process. By using an attosecond two-color interferometric approach in combination with high spectral resolution, we have captured the changes induced by the nuclear motion on the centrifugal barrier that sustains the well-known shape resonance in valence-ionized N-2. We show that despite the nuclear motion altering the bond length by only 2%, which leads to tiny changes in the potential barrier, the corresponding change in the ionization time can be as large as 200 attoseconds. This result poses limits to the concept of instantaneous electronic transitions in molecules, which is at the basis of the Franck-Condon principle of molecular spectroscopy.
60.	Neoričić, L., et al. (author) Resonant two-photon ionization of helium atoms studied by attosecond interferometry 2022 In: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 10 Journal article (peer-reviewed)abstract We study resonant two-photon ionization of helium atoms via the 1s3p, 1s4p and 1s5p P-1(1) states using the 15(th) harmonic of a titanium-sapphire laser for the excitation and a weak fraction of the laser field for the ionization. The phase of the photoelectron wavepackets is measured by an attosecond interferometric technique, using the 17(th) harmonic. We perform experiments with angular resolution using a velocity map imaging spectrometer and with high energy resolution using a magnetic bottle electron spectrometer. Our results are compared to calculations using the two-photon random phase approximation with exchange to account for electron correlation effects. We give an interpretation for the multiple pi-rad phase jumps observed, both at and away from resonance, as well as their dependence on the emission angle.
61.	Petersson, C. L.M., et al. (author) Anisotropic photoemission time delays close to a Fano resonance 2018 In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9 Journal article (peer-reviewed)abstract Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. The process of autoionization, induced by resonant excitation of electrons into discrete states present in the spectral continuum of atomic and molecular targets, is mediated by electron correlation. Here we investigate the attosecond photoemission dynamics in argon in the 20-40 eV spectral range, in the vicinity of the 3s(-1)np autoionizing resonances. We present measurements of the differential photoionization cross section and extract energy and angle-dependent atomic time delays with an attosecond interferometric method. With the support of a theoretical model, we are able to attribute a large part of the measured time delay anisotropy to the presence of autoionizing resonances, which not only distort the phase of the emitted photoelectron wave packet but also introduce an angular dependence.
62.	Ruchon, T., et al. (author) Progress in attosecond technology-application to momentum shearing interferometry of electron wavepackets 2006 In: Optical Fabrication and Testing, OFT 2006. - 1557528187 - 9781557528186 Conference paper (peer-reviewed)abstract The recently demonstrated momentum shearing interferometry technique, aimed at recovering phase information about electronic wave packets (EWP) will be presented. Possibilities to improve this technique will be discussed.
63.	Salgado-Remacha, F. J., et al. (author) Single-shot d-scan technique for ultrashort laser pulse characterization using transverse second-harmonic generation in random nonlinear crystals 2020 In: Optics Letters. - 0146-9592. ; 45:14, s. 3925-3928 Journal article (peer-reviewed)abstract We demonstrate a novel dispersion-scan (d-scan) scheme for single-shot temporal characterization of ultrashort laser pulses. The novelty of this method relies on the use of a highly dispersive crystal featuring antiparallel nonlinear domains with a random distribution and size. This crystal, capable of generating a transverse second-harmonic signal, acts simultaneously as the dispersive element and the nonlinear medium of the d-scan device. The resulting in-line architecture makes the technique very simple and robust, allowing the acquisition of single-shot d-scan traces in real time. The retrieved pulses are in very good agreement with independent frequency-resolved optical grating measurements. We also apply the new single-shot d-scan to a terawatt-class laser equipped with a programmable pulse shaper, obtaining an excellent agreement between the applied and the d-scan retrieved dispersions.
64.	Salieres, P, et al. (author) Angular distributions of high-order harmonics generated by a femtosecond laser 1996 In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075. ; 29:20, s. 4771-4786 Journal article (peer-reviewed)abstract We present a systematic study of the angular distributions of high-order harmonics generated with a femtosecond Cr:LiSrAlF6 laser. We investigate the influence of different parameters, namely laser intensity, nonlinear order, nature of the gas and position of the laser focus relative to the generating medium. We show that when the laser is focused before the atomic medium, harmonics with regular spatial profiles can be generated with reasonable conversion efficiency. Their divergence does not depend directly on the nonlinear order, the intensity or even the nature of the generating gas, but rather on the region of the spectrum the considered harmonic belongs to, which is determined by the combination of the three preceding elements. When the focus is drawn closer to the medium, the distributions get increasingly distorted, becoming annular with a significant divergence for a focus right into-or after-the jet. We perform numerical simulations of the angular distributions. The simulated profiles reproduce remarkably well the experimental trends and are thus used to interpret them.
65.	Varju, Katalin, et al. (author) Angularly resolved electron wave packet interferences 2006 In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:18, s. 3983-3991 Journal article (peer-reviewed)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.
66.	Veyrinas, K., et al. (author) Chromatic aberrations correction of attosecond high-order harmonic beams by flat-top spatial shaping of the fundamental beam 2023 In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 25:2 Journal article (peer-reviewed)abstract Attosecond pulses created by high-order harmonic generation in gases often exhibit strong chromatic aberrations, arising from the broad bandwidth and wavelength-dependent nonlinear light-matter interaction. When the driving laser intensity varies spatially, as for Gaussian driving beams, the apparent source position of the harmonics differs significantly from one order to the next, thus affecting the achievable intensity and duration of the attosecond pulses when they are focused on a target. We show that these chromatic aberrations can be reduced by spatially shaping the fundamental beam to generate high-order harmonics with a driver having a flat-top profile inside the gas medium. By measuring both the intensity profile and wavefront for each harmonic in a plane, we access the extreme ultra-violet (XUV) beam properties and investigate these properties near focus. We observe that controlling chromatic aberrations by flat-top spatial shaping strongly reduces the variation of the XUV spectrum on the beam axis during propagation and, in return, the longitudinal sensitivity of both the temporal profiles and the temporal shifts of the focused attosecond pulses.
67.	Veyrinas, K., et al. (author) High order harmonic generation with spatially shaped flat top driver to control XUV chromatic aberrations 2023 In: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - 9798350345995 Conference paper (peer-reviewed)abstract The XUV beams generated via high order harmonic generation (HHG) in gases have spatial properties evolving with the harmonic order. It leads to chromatic aberrations when the harmonics are focussed so that, locally, the spectral content can change significantly during propagation [1-3] especially near focus.
68.	Zerne, R, et al. (author) Phase-locked high-order harmonic sources 1997 In: Physical Review Letters. - 1079-7114. ; 79:6, s. 1006-1009 Journal article (peer-reviewed)abstract We demonstrate that two harmonic sources generated independently in a xenon gas jet using the same picosecond Nd:YAG laser are locked in phase. The experiment is performed by separating a laser beam into two parallel beams focused at different locations under the nozzle of a gas jet, and therefore producing two independent sources of harmonic radiation, and studying the pattern obtained in the far field when the radiations from these sources interfere. A high and robust fringe visibility is obtained.
69.	Antoine, P, et al. (author) Attosecond pulse trains using high-order harmonics 1996 In: Physical Review Letters. - 1079-7114. ; 77:7, s. 1234-1237 Journal article (peer-reviewed)abstract We demonstrate that high-order harmonics generated by an atom in intense laser field form trains of ultrashort pulses corresponding to different trajectories of electrons that tunnel out of the atom and recombine. Propagation in an atomic jet allows us to select one of these trajectories, leading to a train of pulses of extremely short duration.
70.	Antoine, P, et al. (author) Polarization of high-order harmonics 1997 In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 55:2, s. 1314-1324 Journal article (peer-reviewed)abstract We report measurements and calculations of the polarization state of high-order harmonics generated by a 790-nm Ti:sapphire laser. The problem of completely characterizing the polarization state of a partially polarized radiation in the XUV range is discussed in detail. The comparison between several gases, xenon, argon and neon, and different orders, from the 17th to the 33rd, shows that the rotation angle and ellipticity strongly depends on the position of the harmonic in the spectrum, and in particular, whether it is in the cutoff or in the plateau. In the plateau, the rotation angle is quite large, and the ellipticity follows that of the fundamental, remaining, however, smaller. The radiation is only partially polarized. In contrast, in the cutoff, both rotation angle and ellipticity remain small, independently of the laser ellipticity. Our experimental results compare well with theoretical predictions including the single-atom response and propagation effects.
71.	Antoine, P, et al. (author) Theory of high-order harmonic generation by an elliptically polarized laser field 1996 In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 53:3, s. 1725-1745 Journal article (peer-reviewed)abstract We generalize a recently formulated theory of high-order harmonic generation by low-frequency laser fields [Anne L'Huillier et al., Phys. Rev. A 48, R3433 (1993)] to the case of an elliptically polarized light. Our theoretical description includes both the single-atom response and propagation. Phase matching significantly modifies the results obtained in the single-atom response. The results of our calculations, including propagation for both the intensity and polarization properties of harmonics as a function of laser ellipticity, compare very well with recent experimental observations.
72.	Appi, E., et al. (author) Two phase-matching regimes in high-order harmonic generation 2023 In: Optics Express. - 1094-4087. ; 31:20, s. 31687-31697 Journal article (peer-reviewed)abstract High-order harmonic generation (HHG) provides scalable sources of coherent extreme ultraviolet radiation with pulse duration down to the attosecond time scale. Efficient HHG requires the constructive interplay between microscopic and macroscopic effects in the generation volume, which can be achieved over a large range of experimental parameters from the driving field properties to those of the generating medium. Here, we present a systematic study of the harmonic yield as a function of gas pressure and medium length. Two regimes for optimum yield are identified, supporting the predictions of a recently proposed analytical model. Our observations are independent on the focusing geometry and, to a large extent, on the pulse duration and laser intensity, providing a versatile approach to HHG optimization.
73.	Balla, Prannay, et al. (author) Factor 40 Pulse Post-Compression of 200 W in-Burst Average Power Pulses via Single-Stage Multi-Pass Spectral Broadening 2020 In: 2020 Conference on Lasers and Electro-Optics, CLEO 2020 - Proceedings. - 1092-8081. - 9781943580767 ; 2020-May Conference paper (peer-reviewed)abstract We report nonlinear pulse compression of 1.2-ps, 2-mJ pulses. For spectral broadening, we use a Kr-filled Herriott-type cell with 22-roundtrips. After a chirped-mirror compressor, we measure 30-fs pulses, 80% transmission and an M2 of 1.5×1.7.
74.	Balla, Prannay, et al. (author) Post-compression of picosecond pulses to four optical cycles 2020 In: High Intensity Lasers and High Field Phenomena, HILAS 2020. - 9781557528209 Conference paper (peer-reviewed)abstract We report post-compression of 1.2 ps pulses into the few-cycle regime via multi-pass spectral broadening. We achieve compression factors of 40 in single and 93 in a dual stage scheme using a compact setup.
75.	Balla, Prannay, et al. (author) Postcompression of picosecond pulses into the few-cycle regime 2020 In: Optics Letters. - 0146-9592. ; 45:9, s. 2572-2575 Journal article (peer-reviewed)abstract In this work,we demonstrate postcompression of 1.2 ps laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route toward compact few-cycle sources driven by industrial-grade Yb:YAG lasers at high average power.
76.	Busto, David, et al. (author) Probing electronic decoherence with high-resolution attosecond photoelectron interferometry 2022 In: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 76:7 Journal article (peer-reviewed)abstract Abstract: Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well-known source of decoherence when only one of the particles is measured. Here, we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p2 states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle-integrated measurements, into a dynamic loss of coherence during autoionization. Graphic Abstract: [Figure not available: see fulltext.]. © 2022, The Author(s).
77.	Campi, F., et al. (author) The high intensity HHG beamline at lund laser 2014 In: High Intensity Lasers and High Field Phenomena, HILAS 2014. - 9781557529954 Conference paper (peer-reviewed)abstract We will present the new Lund HHG beamline designed for high photon flux, delivering pulse energies of more than 4 μJ per pulse in the spectral range from 20 eV to 45 eV. Focused XUV intensities above 1014 W/cm2 should become possible.
78.	Chew, S.H., et al. (author) Imaging Localized Surface Plasmons by Femtosecond to Attosecond Time-Resolved Photoelectron Emission Microscopy – “ATTO-PEEM” 2015 In: Attosecond Nanophysics: From Basic Science to Applications. - Weinheim, Germany : Wiley-VCH Verlag GmbH & Co. KGaA. - 9783527411719 ; , s. 325-364 Book chapter (peer-reviewed)
79.	Descamps, D., et al. (author) Application des harmoniques générées dans un jet de gaz : Mesure de sections efficaces d'ionisation des états excités de l'hélium 1999 In: Journal de Physique IV. - : EDP Sciences. - 1155-4339. ; 9:PR5, s. 25-26 Journal article (peer-reviewed)
80.	Descamps, D, et al. (author) Extreme ultraviolet interferometry measurements with high-order harmonics 2000 In: Optics Letters. - 0146-9592. ; 25:2, s. 135-137 Journal article (peer-reviewed)abstract We demonstrate that high-order harmonics generated by short, intense laser pulses in gases provide an interesting radiation source for extreme ultraviolet interferometry, since they are tunable, coherent, of short pulse duration, and simple to manipulate. Harmonics from the 9th to the 15th are used to measure the thickness of an aluminum layer. The 11th harmonic is used to determine the spatial distribution of the electron density of a plasma produced by a 300-ps laser. Electronic densities higher than 2-10(20) electrons/cm(3) are measured. (C) 2000 Optical Society of America. OCIS codes: 190.0190, 190.4160, 190.7110, 120.3180, 140.7240, 350.4500.
81.	Gaarde, Mette, et al. (author) Theory of high-order sum and difference frequency mixing in a strong bichromatic laser field 1996 In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 54:5, s. 4236-4248 Journal article (peer-reviewed)abstract We generalize the recently formulated theory of high-order harmonic generation by low-frequency laser fields to the case of high-order sum and difference frequency mixing in a two-color field of noncommensurate frequencies in the optical-infrared regime. Our theoretical description includes both the single-atom response and propagation. We observe a different behavior of the sum and difference frequency mixing processes, in the single-atom response as well as in the propagation results. The results of our calculations including propagation compare very well with recent experimental observations.
82.	Greer, Mark, et al. (author) Dichotomy in pulmonary graft-versus-host disease evident among allogeneic stem-cell transplant recipients undergoing lung transplantation 2016 In: European Respiratory Journal. - : European Respiratory Society (ERS). - 0903-1936 .- 1399-3003. ; 48:6, s. 1807-1810 Journal article (peer-reviewed)
83.	Guenot, Diego, et al. (author) Measurements of relative photoemission time delays in noble gas atoms 2014 In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 47:24, s. 245602- Journal article (peer-reviewed)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.
84.	Harth, Anne, et al. (author) Compact 200 kHz HHG source driven by a few-cycle OPCPA 2018 In: Journal of Optics (United Kingdom). - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 20:1 Journal article (peer-reviewed)abstract We present efficient high-order harmonic generation (HHG) based on a high-repetition rate, few-cycle, near infrared (NIR), carrier-envelope phase stable, optical parametric chirped pulse amplifier (OPCPA), emitting 6 fs pulses with 9 μJ pulse energy. In krypton, we reach conversion efficiencies from the NIR to the extreme ultraviolet (XUV) radiation pulse energy on the order of ∼10-6 with less than 3 μJ driving pulse energy. This is achieved by optimizing the OPCPA for a spatially and temporally clean pulse and by a specially designed high-pressure gas target. In the future, the high efficiency of the HHG source will be beneficial for high-repetition rate two-colour (NIR-XUV) pump-probe experiments, where the available pulse energy from the laser has to be distributed economically between pump and probe pulses.
85.	He, Xinkui, et al. (author) Interference effects in two-color high-order harmonic generation 2010 In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 82:3 Journal article (peer-reviewed)abstract We study high-order harmonic generation in argon driven by an intense 800 nm laser field and a small fraction of its second harmonic. The intensity and divergence of the emitted even and odd harmonics are strongly modulated as a function of the relative delay between the two fields. We provide a detailed analysis of the underlying interference effects. The interference changes drastically when approaching the cutoff region due to a switch of the dominant trajectory responsible for harmonic generation.
86.	Hergott, JF, et al. (author) XUV interferometry using high-order harmonics: Application to plasma diagnostics 2001 In: Laser and Particle Beams. - 0263-0346. ; 19:1, s. 35-40 Journal article (peer-reviewed)abstract In this paper, we present and compare the two different XUV interferometric techniques using high-order harmonics that have been developed so far. The first scheme is based on the interference between two spatially separated phase-locked harmonic sources while the second uses two temporally separated harmonic sources. These techniques have been applied to plasma diagnostics in feasibility experiments where electron densities up to a few 1020 e[minus sign/cm3 have been measured with a temporal resolution of 200 fs. We present the main characteristics of each technique and discuss their respective potentials and limitations.
87.	Heyl, C. M., et al. (author) Introduction to macroscopic power scaling principles for high-order harmonic generation 2017 In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:1 Journal article (peer-reviewed)abstract This tutorial presents an introduction to power scaling concepts for high-order harmonic generation (HHG) and attosecond pulse production. We present an overview of state-of-the-art HHG-based extreme ultraviolet (XUV) sources, followed by a brief introduction to basic principles underlying HHG and a detailed discussion of macroscopic effects and scaling principles. Particular emphasis is put on a general scaling model that allows the invariant scaling of the HHG process both, to μJ-level driving laser pulses and thus to multi-MHz repetition rates as well as to 100 mJ-or even Joule-level laser pulses, allowing new intensity regimes with attosecond XUV pulses.
88.	Hoff, D., et al. (author) Direct CEP Stabilization of a high-repetition rate, few-cycle OPCPA chain with a single feedback loop, employing a Stereo-ATI 2023 In: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - 9798350345995 Conference paper (peer-reviewed)abstract Today's Carrier-Envelope Phase (CEP) stabilizations of mode-locked oscillators widely used in attosecond science and frequency metrology rely on octave spanning frequency combs and the detection of beating between the blue end and the frequency doubled red end of the same spectrum. This technique was established by the seminal works of Hänsch and co-workers [1], demonstrating the stabilization of optical frequencies from such a frequency comb by transferring the slippage of the CEP (or carrier-envelope offset frequency) into a detectable radio frequency by f-2f interferometry. The requirement of an octave spanning spectrum means that usually some kind of super-continuum generation is involved, which, in practice often is a fragile scheme since wide band oscillators are very prone to instabilities and noise.
89.	Hoff, D., et al. (author) Quantum Beat Spectroscopy of Helium Photoelectrons 2023 In: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - 9798350345995 Conference paper (peer-reviewed)abstract The availability of broadband extreme ultraviolet light sources allows for investigation of electron wave-packets from high lying bound states in atoms [1,2]. The dynamics of these states can be mapped out in the ionization continuum with an overlapping infrared field, which may also uncover new, light induced, dressed states [3]. Here, we carry out a complete characterization of these electron wave-packets using a small number of attosecond pulses.
90.	Jarnac, A., et al. (author) Generation of energetic compressed laser pulses in a planar hollow waveguide for high-order harmonic generation 2019 In: Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015. - 9781467374750 Conference paper (peer-reviewed)abstract We present post-compression of a TW class laser in a planar hollow waveguide. The viability of the compressed pulses for applications in strong-field physics is demonstrated by generating high-order harmonics in a gas jet.
91.	Jimenez-Galan, A., et al. (author) Phase Measurement of a Fano Resonance Using Tunable Attosecond Pulses 2015 In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635, s. 092137-092137 Conference paper (peer-reviewed)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.
92.	Johnsson, Per, et al. (author) Attosecond electron wave packet dynamics in strong laser fields 2005 In: Physical Review Letters. - 1079-7114. ; 95:1, s. 1-013001 Journal article (peer-reviewed)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.
93.	Kovacev, M, et al. (author) Extreme ultraviolet fourier-transform spectroscopy with high order harmonics 2005 In: Physical Review Letters. - 1079-7114. ; 95:22 Journal article (peer-reviewed)abstract We demonstrate a new scheme for extreme ultraviolet (xuv) Fourier-transform spectroscopy based on the generation of two phase-locked high-harmonic beams. It allows us to measure for the first time interferograms at wavelengths as short as 90 nm, and open the perspective of performing high-resolution Fourier-transform absorption spectroscopy in the xuv. Our measurements also demonstrate that a precise control of the relative phase of harmonic pulses can be obtained with an accuracy on an attosecond time scale, of importance for future xuv pump-xuv probe attosecond spectroscopy.
94.	Kovács, K, et al. (author) Multi-parameter optimization of a loose focusing high flux high-harmonic beamline 2019 In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 52:5, s. 055402-055402 Journal article (peer-reviewed)abstract We perform a multi-dimensional parameter scan in the generation of high-order harmonics, with the main purpose to find the macroscopic conditions that optimize the harmonic yield in a specific spectral domain, around 40 eV for this particular case. The scanned parameters are the laser pulse energy, gas pressure, interaction cell position relative to focus and the cell length, while the fixed parameters are chosen to model a loose focusing configuration which is used in many existing laboratories. We performed the simulations with a 3D non-adiabatic model complemented by a detailed analysis of the phase matching mechanisms involved in an efficient harmonic generation. Based on the results we identify a range of parameter combinations that lead to a high yield in the specified spectral domain. The method and results presented here can be the framework for the design and construction of high flux high-order harmonic generation beamlines.
95.	Kühn, Sergei, et al. (author) The ELI-ALPS facility : The next generation of attosecond sources 2017 In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:13 Research review (peer-reviewed)abstract This review presents the technological infrastructure that will be available at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) international facility. ELI-ALPS will offer to the international scientific community ultrashort pulses in the femtosecond and attosecond domain for time-resolved investigations with unprecedented levels of high quality characteristics. The laser sources and the attosecond beamlines available at the facility will make attosecond technology accessible for scientists lacking access to these novel tools. Time-resolved investigation of systems of increasing complexity is envisaged using the end stations that will be provided at the facility.
96.	Laurell, Hugo, et al. (author) Measuring the quantum state of photoelectrons 2023 Journal article (other academic/artistic)abstract A photoelectron, emitted due to the absorption of light quanta as described by the photoelectric effect, is often characterized experimentally by a classical quantity, its momentum. However, since the photoelectron is a quantum object, its rigorous characterization requires the reconstruction of the complete quantum state, the photoelectron's density matrix. Here, we use quantum state tomography to fully characterize photoelectrons emitted from helium and argon atoms upon absorption of ultrashort, extreme ultraviolet light pulses. While in helium we measure a pure photoelectronic state, in argon, spin-orbit interaction induces entanglement between the ion and the photoelectron, leading to a reduced purity of the photoelectron state. Our work shows how state tomography gives new insights into the fundamental quantum aspects of light-induced electronic processes in matter, bridging the fields of photoelectron spectroscopy and quantum information, and offering new spectroscopic possibilities for quantum technology.
97.	Lewenstein, M, et al. (author) Phase of the Atomic Polarization In High-order Harmonic-generation 1995 In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 52:6, s. 4747-4754 Journal article (peer-reviewed)abstract A recently formulated theory of high-order harmonic generation by low-frequency laser fields [Anne L'Huillier et al., Phys. Rev. A 48, R3433 (1993)] allows us to study the phase of the induced atomic dipole moment. We show that this phase exhibits a piecewise-linear dependence on the laser intensity. This dependence can be interpreted in quasiclassical terms, and is related to the action acquired by the electron during its motion in the laser held. The value of the phase, however, is also affected by the quantum effects of tunneling, diffusion, and interference. The phase of the dipole moment considerably influences the conversion efficiency, as well as the coherence properties, of the harmonics generated in macroscopic media.
98.	Lopez, Rodrigo, et al. (author) Amplitude and phase control of attosecond light pulses 2005 In: Physical Review Letters. - 1079-7114. ; 94:3 Journal article (peer-reviewed)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.
99.	Lopez, Rodrigo, et al. (author) Characterization of high-order harmonic radiation on femtosecond and attosecond time scales 2004 In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 78:7-8, s. 835-840 Journal article (peer-reviewed)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.
100.	Lynga, C, et al. (author) Temporal coherence of high-order harmonics 1999 In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 60:6, s. 4823-4830 Journal article (peer-reviewed)abstract Systematic studies of the temporal coherence properties of high-order harmonic radiation are presented. These complement our previous investigations [Bellini et at, Phys. Rev. Lett. 81, 297 (1998)], where we showed the separation of the far-field pattern of high-order harmonics into two distinct spatial regions with different coherence times. Here we show how the coherence time of the inner and outer regions changes as a function of the harmonic order, the laser intensity, and the focusing conditions. Good agreement with the predictions of the semiclassical model of harmonic generation is obtained. [S1050-2947(99)10312-3].

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