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The comparison of high-order harmonic generation of H$_{2}^{+ }$ in a circularly polarized laser pulse combined with a terahertz field and with a static electric field
摘要： By solving a two-dimensional time-dependent Schr?dinger equation we investigate high-order harmonic generation (HHG) for the H+2 molecular ion in a circularly polarized laser pulse (CPLP). A comparison is made between a HHG in a CPLP combined with a terahertz (THz) field and with a static electric field. When the CPLP is combined with a static electric field, it is observed that a double-plateau structure appears, and the harmonic spectrum presents large modulation. With the CPLP with a THz field, a continuum spectrum with a spectral width of about 137 eV from 102 eV to 239 eV can be achieved. The HHG process is studied using the semi-classical three-step model and time-frequency analysis. Our studies show that only one trajectory contributes to HHG when a THz field is added. Furthermore, we present the temporal evolution of the probability density of an electron wave packet, which shows the recombination of electrons at different times.
关键词： circularly polarized laser pulse,quantum path control,high-order harmonic generation
更新于2025-09-23 15:21:01
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Efficiency control of high-order harmonic generation in gases using driving pulse spectral features
摘要： The low conversion efficiency of high-order harmonic generation (HHG) in gases is an insurmountable limitation for many applications, where a considerable photon flux is an instrumental prerequisite. We present a study of the HHG conversion efficiency dependence on the driving laser intensity and analyze the conditions for optimal phase-matching in a loose focusing configuration and long generation medium using a Ti:Sapphire laser. Moreover, by determination of the influence of plasma effects on the driving laser pulse, we observe a correlation between the HHG conversion efficiency and the blueshift of the fundamental pulse. The maximal HHG conversion efficiency is achieved just before the driving laser spectrum is considerably affected by the plasma. Similar behavior is observed in HHG for different noble gases. In this respect, the appearance of a plasma-induced spectral shift in the driving laser might serve as an indication of a substantial loss of HHG conversion efficiency. Consequently, our findings can be exploited to obtain essential information about the laser-plasma interaction process during HHG and can pave the way for a more convenient control of optimal HHG conditions.
关键词： plasma effects,high-order harmonic generation,conversion efficiency,driving laser intensity,spectral blueshift,phase-matching
更新于2025-09-23 15:21:01
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Spectral splitting and phase matching of the macroscopic high-order harmonic generation in intense laser fields
摘要： We theoretically investigate the macroscopic high-order harmonic generation in argon gaseous medium by numerically solving the three-dimensional macroscopic propagation equation, and the results show that the harmonic spectral and spatial profiles of harmonics are gradually splitting with the increasing of the driving laser intensity. This splitting is mainly due to the distortions which the driving field suffers during propagation and the consequence is also on phase matching. To illustrate the physical mechanisms of harmonic splitting, a theoretical analysis of the phase matching is presented. The harmonic spectra from different focus positions reveal that the split is dependent on the focus-gas-jet relative position. Moreover, we demonstrate that the spectral splitting of high harmonics can hardly be observed for neon gas jet due to the high ionization energy.
关键词： phase matching,high-order harmonic generation,intense laser fields,macroscopic propagation,spectral splitting
更新于2025-09-23 15:19:57
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Numerical simulation of a coupled system of Maxwell equations and a gas dynamic model
摘要： It is known that both linear and nonlinear optical phenomena can be produced when the plasmon in metallic nanostructures are excited by the external electromagnetic waves. In this work, a coupled system of Maxwell equations and a gas dynamic model including a quantum pressure term is employed to simulate the plasmon dynamics of free electron fluid in different metallic nanostructures using a discontinuous Galerkin method. Numerical benchmarks demonstrate that the proposed numerical method can simulate both the high order harmonic generation and the nonlocal effect from metallic nanostructures. Based on the switch-on-and-off investigation, we can conclude that the quantum pressure term in gas dynamics is responsible for the bulk plasmon resonance. In addition, for the dielectric-filled nano-cavity, a coupled effective polarization model is further adopted to investigate the optical behavior of bound electrons. Concerning the numerical setting in this work, a strengthened influence of bound electrons on the generation of high order harmonic waves has been observed.
关键词： quantum pressure,Discontinuous Galerkin method,Maxwell equations,nonlocal effect,high order harmonic generation,gas dynamic model
更新于2025-09-23 15:19:57
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Multi-parameter optimization of a loose focusing high flux high-harmonic beamline
摘要： 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.
关键词： XUV flux,high-order harmonic generation,optimization,multi-dimensional parameter scan,numerical simulation
更新于2025-09-19 17:15:36
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Time-dependent optimization of laser-produced molecular plasmas through high-order harmonic generation
摘要： Analysis and characterization of laser-produced plasmas (LPPs) require the advanced methods for determination of different multiparticle component formation and spreading. Time-resolved high-order harmonic generation (HHG) in spreading LPPs allows determining optimal conditions for this process. One of the most important parameters of HHG in LPP is the delay between the heating and driving pulses. We demonstrate that the optimization of delays allows achieving the maximal harmonic yields in LPP created on the surfaces of the solid targets possessing different molar masses (m). The optimal delays (t) for B4C, ZnO, GaP, GaAs, and Ag2S plasmas were determined to be approximately 200, 300, 350, 500, and 700 ns, respectively. These variations of delays correspond to the t1(m)0.5 dependence for different materials. We demonstrate the applicability of the proposed method for analysis of the resonance-enhanced harmonics in atomic and molecular plasmas (Mo and MoS2) and for studies of large perovskite aggregates as potential emitters of harmonics. This diagnostic technique can also be applied to the analysis of the presence of different nanostructures in LPPs through HHG with a high spatiotemporal resolution.
关键词： perovskite aggregates,laser-produced plasmas,molar masses,time-resolved,high-order harmonic generation,optimization,nanostructures,resonance-enhanced harmonics
更新于2025-09-19 17:13:59
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Influence of the polarization of a multielectron atom in a strong laser field on high-order harmonic generation
摘要： We study the ionization and high-order harmonic generation (HHG) in argon by short linearly polarized laser pulses. We compare the populations of atomic orbitals and HHG spectra in a wide range of laser-pulse parameters, taking into account the dynamics of all orbitals based on the time-dependent density-functional theory (TDDFT) and only the most active orbital within the single-active electron (SAE) approximation. At high intensities of laser pulses, the atom polarization leads to suppression in the bound-state depletion due to the screening of the external field. The significant increase in the HHG yield is observed for the TDDFT calculations in comparison with the SAE calculations. The contribution of different orbitals in the TDDFT calculations of HHG spectra is discussed.
关键词： ionization,high-order harmonic generation,atom polarization,argon,TDDFT,laser pulses,SAE approximation
更新于2025-09-19 17:13:59
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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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Effect of laser intensity on quantum trajectories in the macroscopic high-order harmonic generation
摘要： We macroscopically investigate the effect of laser intensity and gas density on quantum trajectories in the high-order harmonic generation of Ne atoms irradiated by few-cycle, 800-nm laser pulses. The time-frequency profile of the harmonics shows that the long quantum trajectory is dominant at both lower and higher gas densities for a low laser intensity. At high laser intensities, the long quantum trajectory plays an important role for lower gas densities, while the short quantum trajectory is dominant at higher gas densities. An analysis of the phase mismatch for high-order harmonic generation shows that the primary emission of the quantum trajectories is determined by dynamic changes in the laser electric field during the propagation process.
关键词： quantum trajectory,high-order harmonic generation
更新于2025-09-19 17:13:59