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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Optically Driven Attosecond Electron Dynamics in III-V Semiconductors
摘要： A fundamental understanding of ultrafast electron dynamics in solids induced by light is of great interest for future high-speed electro-optical devices operating in the petahertz frequency regime. In the last years, a number of publications demonstrated the possibility to resolve and control carrier dynamics in semiconductors and dielectrics on the few- to sub-femtosecond time scale using attosecond transient absorption spectroscopy (ATAS). These experiments were performed with a non-resonant pump pulse, i.e. pump photon energies smaller than the corresponding band gap. Here in contrast, we resolve for the first time the attosecond carrier dynamics induced by a resonant intense laser pulse. We study the attosecond electronic response in gallium arsenide (GaAs), a technologically important narrow band gap semiconductor.
关键词： gallium arsenide,III-V semiconductors,attosecond transient absorption spectroscopy,ultrafast electron dynamics,attosecond electron dynamics
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Attosecond Soft X-Ray Absorption Spectroscopy in Graphite
摘要： X-ray absorption fine-structure (XAFS) spectroscopy is a well-established technique capable to extract information on the electronic and lattice structure of a material with atomic resolution. Analysis of the XAFS spectrum in the near-edge region (XANES) provides information about the electronic configuration. Structural information is extracted from the extended XAFS (EXAFS) spectrum, consisting of several hundreds of eV above the absorption edge. Connecting the spectroscopic capabilities of XAFS technique to high temporal resolution would give the possibility to follow electronic and lattice dynamics in real time. Here, we present the simultaneously access to electronic and lattice parameters via XAFS spectroscopy using isolated attosecond soft X-ray (SXR) pulses covering the entire water window region (280 eV to 540 eV). We demonstrate the novel capabilities of attosecond XAFS (attoXAFS) by identifying the (cid:1)* and (cid:1)* orbital contributions to the density of states in highly oriented pyrolithic graphite (HOPG) simultaneously with the four characteristic bonding distances of graphite’s hexagonal lattice.
关键词： attosecond,graphite,soft X-ray,electronic and lattice dynamics,XAFS spectroscopy
更新于2025-09-11 14:15:04
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Role of quantum orbits in odd-even high harmonic generation from atoms in bichromatic laser fields
摘要： We study high-order harmonic generation from atoms in bichromatic laser fields numerically and analytically. With the weak increase of the second harmonic field, the calculated odd and even HHG spectra differ remarkably from each other in some energy regions. Our analyses reveal that the interference of two neighboring quantum orbits plays an important role in this phenomenon. In particular, we show that with a trajectory-resolved approach, the emission of odd or even harmonics can be effectively controlled in a wide HHG energy region. Our results suggest a potential approach for generating even-harmonic-dominating attosecond pulse.
关键词： odd-even harmonics,bichromatic laser fields,attosecond pulse,quantum orbits,high-order harmonic generation
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Petahertz Magnetization Dynamics
摘要： In contrast to conventional electronics, where only the charge of electrons is considered, spintronics is based on the utilization of both charge and spin. Due to this additional degree of freedom, spintronic devices can potentially provide higher processing speed or better energy efficiency. However, while sub-femtosecond control of the electronic properties of solids has previously been demonstrated, the lack of direct coupling between light and spin has limited the manipulation speed of magnetic properties to the few-tens-of-femtoseconds timescale. Here we introduce a technique able to follow the magnetic properties of a solid with attosecond resolution and demonstrate the direct sub-femtosecond all-optical manipulation of its spin degrees of freedom. We probe the time-evolution of the magnetic and electronic properties of solids and their coupling using a novel atto-XMCD scheme. In our experiment, a circularly polarized attosecond pulse (probe) (~310 as FWHM duration, centered at 66 eV corresponding to the M-edges of Nickel) is transmitted through a thin magnetized Nickel (Ni) film or Nickel-Platinum (Ni/Pt) multilayer sample. Reversing the magnetization direction allows to record the polarization dependent X-Ray absorption of Ni (X-Ray Magnetic Circular Dichroism, XMCD), which directly measures the magnetic moment of the Ni atoms. Dynamics are initiated by a carrier-envelope-phase stable sub-4 fs near-infrared electric laser field (pump). Coincidentally, attosecond transient absorption spectroscopy reveals changes of the electronic properties and gives a clear reference for the arrival of the laser pulse. Our results show an instantaneous response of both, charge and spin, to the laser pulse electric field in the Ni/Pt multilayer sample (Fig.1 a). The exceptionally fast demagnetization in the first 10 fs after laser excitation is the first experimental evidence for theoretically predicted optically induced spin transfer (OISTR): simultaneously with the charge transfer due to electronic excitation, the spin of excited electrons is transferred from the ferromagnetic (Ni) to the paramagnetic (Pt) material in the multilayer sample. This reduces the majority spin in Ni, inducing an instantaneous demagnetization of the ferromagnet. Fig. 1 b shows a reference measurement performed with a Ni film. As OISTR is not possible in pure Ni, no demagnetization happens during the pump laser pulse. To conclude, with our novel experimental scheme we demonstrate sub-femtosecond optical spin manipulation in matter. Access and control of the magnetic properties of solids on the attosecond time-scale paves the way towards spintronic devices operating at Petahertz clock rates.
关键词： Petahertz clock rates,X-Ray Magnetic Circular Dichroism,optically induced spin transfer,attosecond resolution,spintronics
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Quasi-Phase Matching in High Harmonic Generation using Structured Plasmas
摘要： High harmonic generation (HHG) is an important process in attosecond science. Its efficiency is, however, limited to values below 10-5 of the incident power into a single harmonic. Phase matching can increase the efficiency but deals with low ionization rates. Furthermore HHG from laser-produced plasmas has shown some promising advantages in increasing the response of the conversion. These are the appearance of resonantly enhanced harmonics or the efficient generation in carbon or nanoparticle containing plasmas. On the contrary laser-produced plasmas inherently possess a high degree of ionization which hampers any phase-matching scheme with these sources. This dilemma can be circumvented by quasi-phase matching (QPM). In this case the conversion process is suppressed when the harmonics are generated out of phase leading to a quadratic growth of the harmonic intensity with interaction distance. Experimentally QPM can be achieved e.g. by applying a structured conversion medium in a focused driving beam geometry. Here, we show how such a scheme is realized with laser-produced plasmas. The idea of using a structured plasma for QPM is not new [1], but in none of these earlier studies QPM has been optimized for maximum efficiency nor controlled for different regions of the harmonic spectrum.
关键词： laser-produced plasmas,quasi-phase matching,attosecond science,High harmonic generation
更新于2025-09-11 14:15:04
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Controlling polarization of high-order harmonic generation by molecular alignment in a bicircular laser field
摘要： The polarization of high-order harmonic generation in H2+ driven by a counterrotating bichromatic ω/3ω circularly polarized laser field is investigated theoretically. The elliptically polarized harmonics are characterized by ellipticity and rotation angle, where the latter is expanded to [?π /2, π /2] by an optimized definition. We find a critical alignment angle where the ellipticity of high-energy harmonics is almost the same, so an attosecond pulse train with a high degree of polarization can be synthesized. In addition, we find that the rotation angle is always different from the alignment angle by 90? with a small deflection. Thus, we propose a scheme to control the harmonic polarization state by the molecular alignment angle.
关键词： molecular alignment,attosecond pulse,high-order harmonic generation,polarization,bicircular laser field
更新于2025-09-11 14:15:04
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Helicity of harmonic generation and attosecond polarization with bichromatic circularly polarized laser fields
摘要： We theoretically investigate the high-order harmonic generation (HHG) of helium atom driven by bichromatic counter-rotating circularly polarized laser fields. By changing the intensity ratio of the two driving laser fields, the spectral chirality of the HHG can be controlled. As the intensity ratio increases, the spectral chirality will change from positive- to negative-value around a large intensity ratio of the two driving fields when the total laser intensity keeps unchanged. However, the sign of the spectral chirality can be changed from positive to negative around a small intensity ratio of the two driving fields when the total laser intensity changes. At this time, we can effectively control the helicity of the harmonic spectrum and the polarization of the resulting attosecond pulses by adjusting the intensity ratio of the two driving laser fields. As the intensity ratio and the total intensity of the driving laser fields increase, the relative intensity of either the left-circularly or right-circularly polarized harmonic can be enhanced. The attosecond pulses can evolve from being elliptical to near linear correspondingly.
关键词： spectral chirality,attosecond polarization,high-order harmonic generation,bichromatic circularly polarized laser fields
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Interferometric Attosecond Lock-in Measurement of Extreme Ultraviolet Circular Diehroism
摘要： Probing vectorial properties of light-matter interactions requires control over the polarization state of light. The generation of extreme-ultraviolet (XUV) attosecond pulses opened new perspectives in measurements of chiral phenomena. Recently, new methods for polarization control in the XUV range, which are based on manipulation of the high harmonic generation (HHG) process were demonstrated [1-4]. However, the limited polarization control in this regime prevents the development of advanced measurement schemes for weak vectorial signals, which require polarization modulation. In our work [5], we establish an XUV lock-in detection scheme, allowing the isolation and amplification of extremely weak chiral signals, by achieving a dynamical control over the polarization state of the XUV light. We demonstrate a time-domain approach to control and modulate the polarization state. This scheme enables us to characterize the polarization state via an in-situ measurement (see Figure 1a,d,e). Our approach, resembling a birefringent crystal for the visible range, is based on the collinear superposition of two independent, phase-locked, orthogonally polarized XUV sources and the control of their relative delay with sub-cycle accuracy (see Figure 1b). We achieve lock-in detection of XUV magnetic circular dichroism (XMCD) in cobalt, transferring weak amplitude variations into a phase modulation (see Figure 1c), by controlling the relative angle, θ , between the two linearly polarized sources. This approach holds the potential of significantly extending the scope of vectorial measurements to the attosecond and nanometer frontiers.
关键词： attosecond pulses,polarization control,high harmonic generation,extreme-ultraviolet,chiral signals,XUV magnetic circular dichroism,XUV lock-in detection
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - High-Repetition-Rate High-Harmonic Generation Driven by Infrared Free-Electron Lasers
摘要： We present for high-harmonic-generation (HHG) driven by infrared free-electron lasers (FEL), which can be operated at MHz-repetition. Wavelength tunability of FEL enables one to explore HHG from mid-infrared pulses for higher cutoff energies above 1 keV. Plans and status of R&D are also presented.
关键词： x-ray,attosecond,free electron laser,high harmonic generation
更新于2025-09-11 14:15:04
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RMT: R-matrix with time-dependence. Solving the semi-relativistic, time-dependent Schr?dinger equation for general, multielectron atoms and molecules in intense, ultrashort, arbitrarily polarized laser pulses
摘要： RMT is a program which solves the time-dependent Schr?dinger equation for general, multielectron atoms, ions and molecules interacting with laser light. As such it can be used to model ionization (single-photon, multiphoton and strong-field), recollision (high-harmonic generation, strong-field rescattering) and, more generally, absorption or scattering processes with a full account of the multielectron correlation effects in a time-dependent manner. Calculations can be performed for targets interacting with ultrashort, intense laser pulses of long wavelength and arbitrary polarization. Calculations for atoms can optionally include the Breit-Pauli correction terms for the description of relativistic (in particular, spin-orbit) effects.
关键词： electron correlation,R-matrix,ionization,strong-field physics,ultrafast physics,Attosecond physics
更新于2025-09-11 14:15:04