High-order Harmonic Generation Research Articles

Noninteger high-order harmonic generation from extended correlated systems

Noninteger high-order harmonic generation from extended correlated systems

High-order harmonic generation in liquid crystals

Thermotropic liquid crystals are versatile optical materials that exhibit a state of matter intermediate between liquids and solids. Their properties can change significantly with temperature, pressure, or other external factors, leading to different phases. The transport properties within these materials in different phases are still largely unexplored, and their understanding would enable exciting prospects for innovative technological advancements. High-order harmonic spectroscopy proved to be a powerful spectroscopic tool for investigating the electronic and nuclear dynamics in matter. Here, we report the first experimental observation of high-order harmonic generation in thermotropic liquid crystals in two different phase states, nematic and isotropic. We found the harmonic emission in the nematic phase to be strongly dependent on the relative orientation of the driving field polarization with respect to the liquid crystal alignment. Specifically, the harmonic yield has a maximum when the molecules are aligned perpendicularly to the polarization of the incoming radiation. Our results establish the first step for applying high-order harmonic spectroscopy as a tool for resolving ultrafast electron dynamics in liquid crystals with unprecedented temporal and spatial resolution.

High-order harmonic generation in a doped semiconductor by inhomogeneous laser field

High-order harmonic generation in a doped semiconductor by inhomogeneous laser field

Generation of near-circularly polarized high-order harmonics in two-color cross-linearly polarized laser fields

We investigate theoretically the ellipticity of the high-order harmonic generation from the molecule by utilizing two-color cross-linearly polarized laser fields. A significant region of the large ellipticity can be achieved by adjusting the crossing angle and the relative phase between the two laser fields. By controlling the short trajectory, we can obtain the smoother harmonic spectrum. The minimum value observed in the plateau region can be attributed to the two-center interference of the molecule. Furthermore, we investigate the contribution of the two-center interference to the ellipticity of HHG. The underlying physical mechanisms of the ellipticity can be demonstrated by the phase difference and amplitude difference of the x and y components of the harmonics. As a result, we synthesized an isolated attosecond pulse with an ellipticity of 0.98.

Parametric model for high-order harmonic generation with quantized fields

Parametric model for high-order harmonic generation with quantized fields

Coulomb-induced emission time shifts in high-order harmonic generation from H2+

Accurate emission times of high-order harmonic generation (HHG) are vital for high-precision ultrafast detection in attosecond science, but a quantitative analysis of Coulomb effects on this time is absent in the molecular HHG. Here, we investigate the Coulomb-induced emission-time shift in HHG of H2+ with two different internuclear distances R, where the times obtained via the Gabor transform of numerical data from solving the time-dependent Schrödinger equation are used as simulation experiment results. Based on the molecular strong-field approximation, we develop a trajectory-resolved classical model that takes into account the molecular two-center structure. By selecting appropriate electron trajectories and including Coulomb interactions, the classical trajectory method can reproduce Gabor emission times well. This consistence reveals that Coulomb tails cause an emission-time shift of ∼35 as at the R = 2.0 a.u. case and of ∼40-60 as at the R = 2.6 a.u. case under the present laser parameters when compared to the Coulomb-free quantum-orbit model. Our results are of significance to probe the attosecond dynamics via two-center interference.

Isolated-attosecond-pulse high-order harmonic generation of keV x rays

Isolated-attosecond-pulse high-order harmonic generation of keV x rays

Orientation-dependent high-order harmonic generation in HCN: Insights from time-dependent density-functional-theory calculations

Orientation-dependent high-order harmonic generation in HCN: Insights from time-dependent density-functional-theory calculations

Effect of molecular alignment and orientation on elliptically polarized high-order harmonic generation

Effect of molecular alignment and orientation on elliptically polarized high-order harmonic generation

Modified saddle-point method applied to high-order above-threshold ionization and high-order harmonic generation: Slater-type versus asymptotic ground-state wave function

Modified saddle-point method applied to high-order above-threshold ionization and high-order harmonic generation: Slater-type versus asymptotic ground-state wave function

Self-healing high-order harmonic generation from curved relativistic plasma mirrors with Bessel-Gaussian beams

Self-healing high-order harmonic generation from curved relativistic plasma mirrors with Bessel-Gaussian beams

Tunable high-order harmonic generation in GeSbTe nano-films

Abstract High-order harmonic generation (HHG) in solids opens new frontiers in ultrafast spectroscopy of carrier and field dynamics in condensed matter, picometer resolution structural lattice characterization and designing compact platforms for attosecond pulse sources. Nanoscale structuring of solid surfaces provides a powerful tool for controlling the spatial characteristics and efficiency of the harmonic emission. Here we study HHG in a prototypical phase-change material Ge2Sb2Te5 (GST). In this material the crystal phase can be reversibly changed between a crystalline and amorphous phase by light or electric current mediated methods. We show that optical phase-switching is fully reversible and allows for dynamic control of harmonic emission. This introduces GST as new addition to materials that enable flexible metasurfaces and photonic structures that can be integrated in devices and allow for ultrafast optical control.

Quantum mechanical modeling of high-intensity laser pulse interaction with hydrogen atom with considering the magnetic field and polarization

In the study of the non-relativistic interaction between high-intensity femtosecond laser pulses and atoms, the influence of the magnetic field is commonly overlooked. This work investigates the effects of the magnetic field in the high-intensity few-cycle laser pulses with non-relativistic intensity of 3.5×1014W/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3.5 \ imes 10^{14} { }\\;\\;{\ ext{W}}/{\ ext{cm}}^{2}$$\\end{document} at the center wavelength of 800 nm on the high-order harmonic generation (HHG), attosecond pulse train (APT), isolated attosecond pulse (IAP), and the electron trajectory in the hydrogen atom, employing the numerical solution of the time-dependent Schrödinger equation in three dimensions (3D-TDSE). Two polarizations, linear and circular, are considered. A comparison with the scenario where the magnetic field is not considered shows that the magnetic field can apply significant corrections to the results. Particularly, considering the magnetic field for circular polarization can make the cutoff frequency of HHG coincide with the semi-classical relationship of ħωc=Ip+3.17Up\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbar {\\upomega }_{{\ ext{c}}} = {\ ext{I}}_{{\ ext{p}}} + 3.17{\ ext{U}}_{{\ ext{p}}}$$\\end{document}, a case that for circular polarization does not exist without considering the magnetic field. Moreover, accounting for the magnetic field leads to a reduction in the attosecond pulse duration for circular polarization for APT (360as\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$360{\ ext{ as}}$$\\end{document} versus 241as\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$241{\ ext{ as}}$$\\end{document}) and for IAP (834as\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$834{\ ext{ as}}$$\\end{document} versus 602as\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$602{\ ext{ as}}$$\\end{document}). Additionally, the difference in production efficiency of HHG and APT between linear and circular polarization is reduced by two orders of magnitude, when magnetic field is considered. Although considering the magnetic field complicates the electron trajectory, especially for circular polarization, however, our quantum model provides enhanced insight into how the interaction works, especially when and where the electron collides with the parent nucleus. In this case, the quantum mechanical modeling largely covers the huge difference of not considering the magnetic field in the results predicted by other works.

High-order harmonic generation in helium: A comparison study

High-order harmonic generation in helium: A comparison study

Role of localized electronic states in high-order harmonic generation from doped semiconductors

Role of localized electronic states in high-order harmonic generation from doped semiconductors

Sub-cycle strong-field tunneling dynamics in solids

Tunneling ionization is a crucial process in the interaction between strong laser fields and matter which initiates numerous nonlinear phenomena including high-order harmonic generation, photoelectron holography, etc. Both adiabatic and nonadiabatic tunneling ionization are well understood in atomic systems. However, the tunneling dynamics in solids, especially nonadiabatic tunneling, has not yet been fully understood. Here, we study the sub-cycle resolved strong-field tunneling dynamics in solids via a complex saddle-point method. We compare the instantaneous momentum at the moment of tunneling and the tunneling distances over a range of Keldysh parameters. Our results demonstrate that for nonadiabatic tunneling, tunneling ionization away from Γ point is possible. When this happens the electron has a nonzero initial velocity when it emerges in the conduction band. Moreover, consistent with atomic tunneling, a reduced tunneling distance as compared to the quasi-static case is found. Our results provide remarkable insight into the basic physics governing the sub-cycle electron tunneling dynamics with significant implications for understanding subsequent strong-field nonlinear phenomena in solids.

Caustic effects on high-order harmonic generation in graphene

Caustic effects on high-order harmonic generation in graphene

High-order harmonic generation in graphene quantum dots in the field of an elliptically polarized pulse

High-order harmonic generation in graphene quantum dots in the field of an elliptically polarized pulse

Control of quantum paths in harmonic generation through orthogonal fields specific frequency ratios

By solving a two-dimensional, time-dependent Schrödinger equation, we investigate high-order harmonic generation for the H2+ molecular ion in orthogonally polarized two-color laser pulses. We find that harmonic generation depends on the frequency ratio n=ωyωx . When the wavelength is 800 nm and n = 1.2, the harmonic plateau becomes smoother, and the quantum orbital interference decreases. We change the fundamental wavelength and find that the harmonic spectrum exhibits a supercontinuum structure, and the quantum orbital is controllable. When the wavelength is 1600 nm and 2000 nm, and n = 1.2, we gain a deeper understanding of the physical process of harmonics. We have provided the time-frequency distribution and the probability density of an electron wave packet picture. Next, we analyzed the impact of the carrier-envelope phase on harmonics, and we combined Lissajous figures to continue our analysis. The research results find that when the carrier-envelope phase is 0, 0.5π, π, and 1.5π, the harmonic intensity becomes higher, and all exhibit a supercontinuum structure. We chose certain orders of harmonics, and isolated attosecond pulses can be synthesized.

Angle-dependent high-order harmonic generation in a topological phase transition of monolayer black phosphorous

Angle-dependent high-order harmonic generation in a topological phase transition of monolayer black phosphorous