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The effect of target thickness on the efficiency of high-order harmonics generated from laser-driven overdense plasma target
摘要： In this paper, we analytically and numerically studied the impact of the target thickness on the efficiency of laser-plasma based high-order harmonics generation (HHG). The optimal parametric region is acquired where the laser normalized amplitude a0, the target density ne and thickness d0 satisfy the relation: a0nc/ne < d0 < a0nc/2ne. In this region, the laser can partially penetrate the target, leading to efficient acceleration of the target. Meanwhile, the target is thick enough to oscillate along the rising edge of the laser without being broken, which guarantees the occurrence of HHG. Both one-dimensional and two-dimensional particle-in-cell simulation results verify our optimal target thickness theory, and a single attosecond pulse with I = 3.0 × 1020 W cm?2 is generated under the driving of 8.6 × 1020 W cm?2, which is several hundred times more intense than that from a thick target.
关键词： the Doppler effect,conversion efficiency,high-order harmonics,intense laser
更新于2025-09-23 15:19:57
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Laser-driven tunneling photocurrent as a source of midinfrared to microwave multidecade supercontinua yoked to high-order harmonics
摘要： Electron tunneling induced by a strong-field laser driver can lead to an ultrafast stepwise buildup of the photoelectron density ρ. When the laser field is strong enough, each such step in the temporal profile of ρ is confined well within the field cycle, providing an ultrabroadband, multidecade force that drives the photoelectron current j. However, whether or not the photocurrent can emit electromagnetic radiation with such an extraordinarily broad spectrum depends on the damping, which defines the low-frequency cutoff in the spectrum of this radiation. We show that, with a suitable choice of the gas pressure and parameters of the laser driver, the laser-induced tunneling photocurrent can serve as a source of a remarkably broadband electromagnetic radiation with a multidecade spectrum stretching from the vacuum ultraviolet all the way down to the microwave range. We demonstrate that the supercontinuum fields emitted by individual photocurrent steps, induced by different field half cycles, can coherently combine, giving rise to well-resolved high-order harmonics on the high-frequency end of the spectrum yoked to a bright midinfrared to microwave supercontinuum, dominating the long-wavelength part of the multidecade radiation output.
关键词： high-order harmonics,photocurrent,supercontinua,microwave,midinfrared,laser-driven tunneling
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
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Intense vortex high-order harmonics generated from laser-ablated plume
摘要： In this study, we demonstrate intense extreme-ultraviolet optical vortices generated using laser-ablation plume as the nonlinear medium. We used two types of plumes that are known to generate intense high-order harmonics for driving lasers with Gaussian beam profiles, but through different mechanisms, namely, carbon (diatomic carbon molecules) and tin (resonance with the autoionizing state). We find that the harmonic fluxes for diatomic carbon molecules are similar for Gaussian and vortex driving fields. However, for harmonics from the autoionizing state of tin (~26.3 eV), the enhancement factor of the resonant harmonic intensity decreases by ~50% when using the vortex driving field. The intense extreme-ultraviolet optical vortices demonstrated in this study will be useful for many applications including a material characterization technique known as optical angular momentum dichroism as well as the spectroscopy of spin-forbidden electronic transitions.
关键词： optical angular momentum dichroism,laser-ablation plume,spin-forbidden electronic transitions,extreme-ultraviolet optical vortices,high-order harmonics,diatomic carbon molecules,autoionizing state
更新于2025-09-11 14:15:04