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Reconstruction of attosecond pulses in the presence of interfering dressing fields using a 100 kHz laser system at ELI-ALPS
摘要： Attosecond Pulse Trains (APT) generated by high-harmonic generation (HHG) of high-intensity near-infrared (IR) laser pulses have proven valuable for studying the electronic dynamics of atomic and molecular species. However, the high intensities required for high-photon-energy, high-flux HHG usually limit the class of adequate laser systems to repetition rates below 10 kHz. Here, APT’s generated from the 100 kHz, 160 W, 40 fs laser system (HR-1) currently under commissioning at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) are reconstructed using the Reconstruction of Attosecond Beating By Interference of two-photon Transitions (RABBIT) technique. These experiments constitute the first attosecond time-resolved photoelectron spectroscopy measurements with attosecond pulses performed at 100 kHz repetition rate and one of the first experiments performed at ELI-ALPS in the framework of projects commissioning its newly installed technologies. These RABBIT measurements were taken with an additional IR field temporally locked to the extreme-ultraviolet APT, resulting in an atypical ω beating. We show that the phase of the 2ω beating recorded under these conditions is strictly identical to that observed in standard RABBIT measurements within second-order perturbation theory. This work highlights an experimental simplification for future experiments based on attosecond interferometry (or RABBIT), which is particularly useful when lasers with high average powers are used.
关键词： photoelectron spectroscopy,High-harmonic generation,attosecond,RABBIT
更新于2025-09-23 15:19:57
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Giant Isolated Attosecond Pulses from Two-Color Laser-Plasma Interactions
摘要： A new regime in the interaction of a two-color (ω; 2ω) laser with a nanometer-scale foil is identified, resulting in the emission of extremely intense, isolated attosecond pulses—even in the case of multicycle lasers. For foils irradiated by lasers exceeding the blow-out field strength (i.e., capable of fully separating electrons from the ion background), the addition of a second harmonic field results in the stabilization of the foil up to the blow-out intensity. This is then followed by a sharp transition to transparency that essentially occurs in a single optical cycle. During the transition cycle, a dense, nanometer-scale electron bunch is accelerated to relativistic velocities and emits a single, strong attosecond pulse with a peak intensity approaching that of the laser field.
关键词： two-color laser,laser-plasma interactions,attosecond pulses,coherent synchrotron emission
更新于2025-09-23 15:19:57
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Attosecond Dynamics of Photoexcitation of the Hydrogen Atom by Ultrashort Laser Pulses
摘要： The dynamics of photoexcitation of the hydrogen atom in the discrete and continuous spectra under the action of laser pulses in the attosecond range of time and pulse durations has been analyzed using perturbation theory. It is shown that over time interval shorter than or on the order of pulse duration, the time dependence of the photoexcitation probability is generally oscillating by nature. It has been established that for certain values of parameters, the envelope of this dependence has a peak, the position of which is determined by the pulse duration and carrier frequency.
关键词： Perturbation theory,Photoexcitation,Hydrogen atom,Attosecond dynamics,Ultrashort laser pulses
更新于2025-09-23 15:19:57
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Attosecond imaging of molecules using high harmonic spectroscopy
摘要： The availability of attosecond-duration extreme ultraviolet or soft X-ray light sources has opened up new fields of research in atomic and molecular physics. These pulses can be as short as 50 as, fast enough to freeze the motion of electrons within molecules, to resolve how electrons rearrange themselves after the removal of an electron and to study electron–electron correlations. Gas-phase molecules can be aligned in space using short laser pulses, permitting the measurement of molecular parameters in the molecular frame. Aligned molecules can be photoionized using a train of attosecond pulses, enabling the complete characterization of the partial waves making up the photoelectron angular distributions. Using a recolliding electron in the high harmonic process allows complex transition dipole matrix elements to be recorded (including their amplitude and phase) in the molecular frame. High harmonic spectroscopy makes it possible to image molecular orbitals and for unimolecular chemical reactions to be followed with femtosecond resolution. For example, the behaviour around conical intersections can be probed. Charge migration within molecules can be observed with sub-femtosecond resolution.
关键词： high harmonic spectroscopy,electron dynamics,charge migration,molecular orbitals,attosecond imaging
更新于2025-09-19 17:15:36
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High-flux ultrafast extreme-ultraviolet photoemission spectroscopy at 18.4?MHz pulse repetition rate
摘要： Laser-dressed photoelectron spectroscopy, employing extreme-ultraviolet attosecond pulses obtained by femtosecond-laser-driven high-order harmonic generation, grants access to atomic-scale electron dynamics. Limited by space charge effects determining the admissible number of photoelectrons ejected during each laser pulse, multidimensional (i.e. spatially or angle-resolved) attosecond photoelectron spectroscopy of solids and nanostructures requires high-photon-energy, broadband high harmonic sources operating at high repetition rates. Here, we present a high-conversion-efficiency, 18.4-MHz-repetition-rate cavity-enhanced high harmonic source emitting 5 × 10^5 photons per pulse in the 25-to-60-eV range, releasing 1 × 10^10 photoelectrons per second from a 10-μm-diameter spot on tungsten, at space charge distortions of only a few tens of meV. Broadband, time-of-flight photoelectron detection with nearly 100% temporal duty cycle evidences a count rate improvement between two and three orders of magnitude over state-of-the-art attosecond photoelectron spectroscopy experiments under identical space charge conditions. The measurement time reduction and the photon energy scalability render this technology viable for next-generation, high-repetition-rate, multidimensional attosecond metrology.
关键词： attosecond science,photoelectron spectroscopy,high-harmonic generation,cavity enhancement,ultrafast lasers
更新于2025-09-19 17:15:36
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Attosecond Streaking Time Delays: Finite-Range Interpretation and Applications
摘要： We review theoretical studies of the attosecond streaking time delay concept in photoionization via the investigation of the electron dynamics in the streaking field after the transition of the photoelectron into the continuum upon absorption of an extreme ultraviolet photon. Based on the results, a so-called finite range interpretation was introduced, which highlighted that the delay is accumulated until the streaking pulse ends and, hence, over a finite range of the potential of the parent ion. Following a discussion of the analysis leading to this interpretation, we summarize a few applications which provide insights into different aspects of the streaking time delay concept in photoionization. Besides a review of previously presented results, we give an analysis of the relevance of the first half-cycle of the streaking field and an outlook regarding the perspective of using the streaking method to resolve dynamical changes in the potential that the photoelectron explores during its propagation in the continuum.
关键词： attosecond measurement techniques,streaking time delays,photoionization,ultrafast laser science
更新于2025-09-19 17:15:36
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Femtosecond Laser-Micromachining of Glass Micro-Chip for High Order Harmonic Generation in Gases
摘要： We report on the application of femtosecond laser micromachining to the fabrication of complex glass microdevices, for high-order harmonic generation in gas. The three-dimensional capabilities and extreme flexibility of femtosecond laser micromachining allow us to achieve accurate control of gas density inside the micrometer interaction channel. This device gives a considerable increase in harmonics’ generation efficiency if compared with traditional harmonic generation in gas jets. We propose different chip geometries that allow the control of the gas density and driving field intensity inside the interaction channel to achieve quasi phase-matching conditions in the harmonic generation process. We believe that these glass micro-devices will pave the way to future downscaling of high-order harmonic generation beamlines.
关键词： femtosecond laser micromachining,attosecond science,high order harmonic generation,de laval gas micro nozzle
更新于2025-09-19 17:13:59
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Attosecond pulse shaping using a seeded free-electron laser
摘要： Attosecond pulses are central to the investigation of valence- and core-electron dynamics on their natural timescales1–3. The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high-order harmonic generation4–7. Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters8,9, multilayer mirrors10 and manipulation of the driving field11. 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 millijoules12,13. Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot-to-shot14–16. Here we report reproducible generation of high-energy (microjoule level) attosecond waveforms using a seeded free-electron laser17. 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.
关键词： high-order harmonic generation,Attosecond pulses,temporal reconstruction,free-electron laser
更新于2025-09-19 17:13:59
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Effects of inhomogeneous laser field in time and space on the generation of broad spectral continuum and ultrashort attosecond pulse
摘要： The inhomogeneous effects of laser field in time and space on the generations of high-order harmonic spectra and attosecond pulses from He atom have been investigated with the assistance of the frequency-chirping technique and the metallic nanostructure. We find that in different combinations of chirps and spatial inhomogeneous effects, not only can the harmonic cutoff be extended, but the single harmonic emission peak (HEP) can also be selected to contribute to the spectral continuum. In detail, with the combinations of (i) symmetric chirp in frequency and positive inhomogeneous effect in space or (ii) asymmetric down chirp in frequency and negative inhomogeneous effect in space, two broad spectral continua with bandwidths of 496 eV and 480 eV can be obtained. Further, by properly adding IR or UV controlling pulse, the harmonic emission efficiency can be enhanced by several orders of magnitude. The enhancement of harmonic yield from adding UV pulse is higher than that from adding IR pulse. Moreover, the difference of harmonic enhancement between UV combined field and IR combined field is much more obvious at lower controlling laser intensity. Through analyzing the ionization probability, we find that the higher enhancement of harmonic yield from UV combined field is because of UV-resonance-enhancement-ionization between the ground state and the excited state of He atom. Finally, by properly superposing some harmonics, a number of attosecond pulses with pulse durations of 45 as can be obtained.
关键词： frequency-chirping technique,High-order harmonic generation,two-color field,inhomogeneous effect in space,ultrashort attosecond pulse
更新于2025-09-19 17:13:59
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Generation of Neara??Circularly Polarized Attosecond Pulse with Tunable Helicity by Unidirectionally Rotating Laser Field
摘要： A method to produce circularly polarized attosecond pulses with tunable helicity from CO molecule by using an unidirectionally rotating laser field is proposed. It is found that broadband harmonic supercontinuum with circular polarization can be generated from the oriented CO molecule. This enables the production sub-100 attosecond isolated pulse with the ellipticity as high as 0.9 at the macroscopic level. Moreover, the helicity of the generated high-order harmonics and the attosecond pulse can be tuned by adjusting the orientation of the CO molecule. This method will be beneficial for the studies on chiral-specific dynamics and magnetic circular dichroism on an attosecond time scale.
关键词： attosecond pulses,tunable helicity,high-order harmonics,rotating laser fields
更新于2025-09-19 17:13:59