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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) - High-Harmonic Probe for Relativistic Laser-Matter Interactions Driven by Ultrashort Pulses in the Mid-Infrared
摘要： High-order harmonic generation (HHG) is one of the central effects in strong-field nonlinear-optical physics. Within the past two decades, HHG has been at the heart of a paradigm-shifting breakthrough to attosecond physics. Much less limelight has been given to the ability of HHG to serve as a highly sensitive and in many ways unique analytical tool. When used in this modality, HHG can help detect and understand ultrafast electron dynamics in complex gas-phase, solid-state, and laser-plasma systems. Here, we extend this concept by using HHG as a probe for relativistic laser–matter interactions driven by ultrashort pulses in the mid-infrared.
关键词： mid-infrared,relativistic laser–matter interactions,ultrashort pulses,High-order harmonic generation
更新于2025-09-12 10:27:22
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Odd–even harmonic generation from oriented CO molecules in linearly polarized laser fields and the influence of the dynamic core-electron polarization
摘要： We present a detailed theoretical study of the odd–even harmonics generated from the polar molecule CO by the method based on numerically solving the time-dependent Schro¨dinger equation within the single-active-electron approximation. First, we reproduce the pure even harmonic generation of CO predicted theoretically by Hu et al. using the time-dependent density functional theory [H. Hu et al., Phys. Rev. Lett., 2017, 119, 173201]. Then, based on the Floquet approach, we are able to attribute this behavior to the half-cycle mirror symmetry of the molecule–field system when the polar molecule is perpendicular to the laser polarization. By numerical simulations, we show that this symmetry is broken at orientation angles other than 901 resulting in the odd–even harmonic generation and a non-trivial even-to-odd harmonics ratio strongly dependent on the molecular orientation. Furthermore, we investigate the influence of the dynamic core-electron polarization (DCeP) on the odd–even behavior near the cutoff of the high-order harmonic spectra. We emphasize that the DCeP effect is noticeable for the odd harmonics only.
关键词： time-dependent Schro¨dinger equation,high-order harmonic generation,polar molecule CO,Floquet approach,dynamic core-electron polarization,single-active-electron approximation
更新于2025-09-12 10:27:22
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Behavioral study of high-order harmonics and attosecond pulse generation via bichromatic driving laser fields
摘要： High-order harmonics intensity and subsequently attosecond pulses which are generated after the interaction of some two color femtosecond pulses with helium ions are studied in this paper. Cutoff frequency in the high-order harmonics' intensity spectrum, maximum ionization probability, attosecond pulse intensity and duration in this research are investigated versus the frequency spacing of the two color driving pulse elements (δω). It is seen that the cutoff frequency decays exponentially by δω, whereas generation of the most powerful and shortest attosecond pulses as well as the maximum ionization probability occurs around the value of δω = 0 (i.e., for the single color pulses). However, the longest attosecond pulses are generated for the case of δω = 0.8 ω0 (in which ω0 is the frequency of the fundamental pulse). Finally, the most isolated attosecond pulses are generated for the case in which δω = 1.25 ω0.
关键词： Attosecond,helium ion,two color,High order harmonic generation
更新于2025-09-12 10:27:22
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High-order harmonic generation using quasi-phase matching and two-color pump in the plasmas containing molecular and alloyed metal sulfide quantum dots
摘要： As high-order harmonic emitters, quantum dots are produced through laser-induced plasmas. Subsequently, we generate high-order harmonics with 800-nm and 30-fs pulses from laser-produced plasmas containing quantum dots of different metal sulfides (Ag2S, CdS, and Cd0.5Zn0.5S). The high-order harmonic generation is analyzed using different approaches, including two-color (800 nm + 400 nm) pump, application of alloyed quantum dots, and quasiphase matching of interacting waves. We discuss the self-phase modulation induced splitting of harmonics, the difference in the application of thick and thin crystals for second harmonic (400 nm) emission during two-color pumping of the quantum dot plasma, the spatial modulation of the quantum dot plasma for quasiphase matching, and the comparison of harmonic yields from monomer and quantum dot plasmas. This study allows us to determine the mechanisms of coherent extreme ultraviolet radiation generation using a few nanometer-sized emitters as well as optimal methods for further enhancing the high-order harmonic generation efficiency.
关键词： laser-produced plasmas,quantum dots,high-order harmonic generation,quasiphase matching,two-color pump
更新于2025-09-12 10:27:22
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Coulomb effect on the dynamics of atoms in a strong elliptical laser field: Unification of the excitation and ionization
摘要： We investigate the Coulomb effect on the dynamics of atoms in a strong elliptical laser ?eld by solving the three-dimensional time-dependent Schr?dinger equation with and without the photoelectron core Coulomb interactions and ?nd that the Coulomb effect plays an important role for the excitation and ionization processes, while it is less important for the high-order harmonic generation. Our calculation results can serve as a benchmark for other approximative methods. Looking at the photoelectron momentum distribution, we ?nd that the Coulomb effect is important for the momentum distribution in the polarization plane and less important for the momentum distributions along the normal direction perpendicular to the polarization plane. Similar to the photoabsorption in a weak ?eld, we demonstrate that the excitation and ionization can be treated in a uni?ed way, which implies the low-energy photoelectron distributions can be connected with the populations of highly excited states.
关键词： photoelectron momentum distribution,Coulomb effect,ionization,high-order harmonic generation,excitation,strong elliptical laser field
更新于2025-09-12 10:27:22
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Resonance Enhancement in Laser-Produced Plasmas (Concepts and Applications) || Resonance Processes at Different Conditions of Harmonic Generation in Laser-Produced Plasmas
摘要： Resonance Processes at Different Conditions of Harmonic Generation in Laser-Produced Plasmas
关键词： resonance enhancement,laser-produced plasmas,picosecond pulses,high-order harmonic generation,harmonic generation
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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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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Light for brevity
摘要： The shortest time interval controlled by a human being is the duration of a light pulse as short as only 100 attoseconds, i.e., 10-16 s. This “attosecond” light pulse belongs to the extreme ultraviolet range (XUV) of the electromagnetic spectrum, with central photon energy typically between 20 and 200 eV. Related to its brevity, an attosecond pulse has a broad bandwidth covering tens of eV. These are natural time and energy scales to study electron dynamics in atoms and molecules.
关键词： ultrafast atomic and molecular physics,high-order harmonic generation,attosecond pulses,electron dynamics
更新于2025-09-10 09:29:36