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Dynamical distortions of structural signatures in molecular high-order harmonic spectroscopy
摘要： We study the signature of two-center interferences in molecular high-order harmonic spectra, with an emphasis on the spectral phase. With the help of both ab initio computations based on the time-dependent Schr?dinger equation and the molecular strong-field approximation (SFA) as developed by Chiril? et al. [Phys. Rev. A 73, 023410 (2006)] and Faria [Phys. Rev. A 76, 043407 (2007)], we observe that the phase behavior is radically different for the short and the long trajectory contributions. By means of Taylor expansions of the molecular SFA, we link this effect to the dynamics of the electron in the continuum. More precisely, we find that the value of the electric field at recombination time plays a crucial role in the shape of the destructive interference phase jump.
关键词： molecular spectroscopy,spectral phase,strong-field approximation,two-center interferences,time-dependent Schr?dinger equation,high-order harmonic generation
更新于2025-09-23 15:23:52
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Pathways to excitation of atoms with bicircular laser pulses
摘要： We study the excitation of the hydrogen atom by bichromatic circularly polarized laser pulses using numerical solutions of the time-dependent Schr?dinger equation. The results are in agreement with the selection rules for multiphoton processes in such fields, namely, excited states are populated in which orbital angular momentum and magnetic quantum numbers are either both odd or both even, independent of the relative helicity, peak intensity, and pulse duration of the pulses. For co-rotating pulses the results show that excitation predominantly proceeds to states with magnetic quantum number of the same helicity as the laser pulses. Besides pathways via direct photon absorption from the ground state our results indicate that a transfer of population among the Rydberg states occurs via (cid:2)-type transitions. In the case of counter-rotating pulses the largest excitation probability is found for Rydberg states that differ in magnetic quantum number by (cid:3)m = ±3. This pattern allows us to estimate how many photons from each of the two bichromatic fields have been absorbed. Finally, we confirm that a population in Rydberg states beyond a maximum orbital angular quantum number is unlikely.
关键词： Rydberg states,hydrogen atom,bichromatic circularly polarized laser pulses,time-dependent Schr?dinger equation,multiphoton processes
更新于2025-09-23 15:21:01
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Simulation of a hydrogen atom in a laser field using the time-dependent variational principle
摘要： The time-dependent variational principle is used to optimize the linear and nonlinear parameters of Gaussian basis functions to solve the time-dependent Schr?dinger equation in one and three dimensions for a one-body soft Coulomb potential in a laser field. The accuracy is tested comparing the solution to finite difference grid calculations using several examples. The approach is not limited to one particle systems and the example presented for two electrons demonstrates the potential to tackle larger systems using correlated basis functions.
关键词： laser field,time-dependent variational principle,time-dependent Schr?dinger equation,Gaussian basis functions,soft Coulomb potential
更新于2025-09-23 15:19:57
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Analysis of two-color laser-induced electron emission from a biased metal surface using an exact quantum mechanical solution
摘要： Photoelectron emission from solids, as driven by high-intensity lasers, offers a platform for the coherent control of electron motion on ultrashort spatiotemporal scales. By solving the time-dependent Schr?dinger equation, we present an exact analytical solution for the nonlinear ultrafast electron emission from a dc-biased metal surface illuminated by two-color laser fields. We systematically examine the combined effects of a dc electric field and two-color laser fields. In addition to the remarkable tunability of electron emission processes due to interference from two-color laser fields, we find that a strong dc electric field not only opens up more tunneling emission channels, but also introduces intense modulation to the emission current. We find surprising results that strong current modulation (with respect to the phase difference of the two-color lasers) persists (>70%), even with a large dc bias (i.e., ratio of the electric fields for dc : fundamental laser : second-harmonic laser ～= 1 : 0.5 : 0.07). In the meantime, the average emission current level increases by about three orders of magnitude relative to the case of zero dc bias. Application of our model to time-resolved photoelectron spectroscopy is exemplified and shows that the dynamics of the n-photon excited states depends strongly on the applied dc field. Our study suggests a practical way to maintain a strong modulation to high current photoemission, by the addition of a large dc bias for two-color laser-induced electron emission.
关键词： dc electric field,two-color laser fields,ultrafast electron emission,photoelectron emission,time-dependent Schr?dinger equation
更新于2025-09-23 15:19:57
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Dependence of direct and rescattered photoelectron spectra of fluorine anions on orbital symmetry in a short laser pulse
摘要： We theoretically investigate the photoelectron spectra of ?uorine anions by a few-cycle linearly polarized laser pulse for different atomic orbitals, which are calculated by an exact solution to the time-dependent Schr?dinger equation and by the strong-?eld approximation, respectively. Through the comparison of results by both methods, we show that the initial orbital symmetry strongly affects the main shape of the photoelectron spectra. Based on the saddle-point method, we ?nd that the orbital symmetry only affects the intracycle interference for the low-energy electron spectra. More importantly, it is found that the elastic scattering differential cross section leaves different ?ngerprints in the photoelectron spectra for atomic orbitals with different magnetic quantum numbers.
关键词： ?uorine anions,laser pulse,photoelectron spectra,elastic scattering differential cross section,time-dependent Schr?dinger equation,orbital symmetry,strong-?eld approximation,saddle-point method
更新于2025-09-23 15:19:57
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Selection of the magnetic quantum number in resonant ionization of neon using an XUV-IR two-color laser field
摘要： A recent experiment [Villeneuve et al. Science 356, 1150 (2017)] has shown that two-color photoionization of neon by the combination of an attosecond XUV pulse train and a moderately strong, linearly polarized IR pulse can preferentially produce photoelectrons with orbital angular quantum number l = 3 (f-wave) and magnetic quantum number m = 0. This result was rationalized by the occurrence of different Stark shifts of m = 0 and |m| = 1 sub-levels in the IR laser field. Here we perform 3D time-dependent Schrodinger equation calculations with a neon effective potential to identify the mechanism for the selective excitation and ionization of m = 0 sub-levels. Calculations of the ionization and excitation yields as a function of the IR intensity and the XUV and IR photon energy reveal that a coupling between two dominant ionization channels involving 3p and 3d intermediate excitations is responsible for the observed m-level selectivity. We compare calculated and measured photoelectron velocity map images and ionization yields over a range of IR intensities and XUV and IR photon energies, and confirm that the m = 0 or |m| = 1 channel, and thus a single set of the quantum numbers, (Jion, l, m), can be selected by an appropriate choice of these parameters.
关键词： photoelectron velocity map images,XUV-IR laser field,neon,time-dependent Schrodinger equation,two-color photoionization,magnetic quantum number,Stark shifts
更新于2025-09-23 15:19:57
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Two-Electron Interference in Strong-Field Ionization of He by a Short Intense Extreme Ultraviolet Laser Pulse
摘要： Double ionization of helium by a single intense (above 1018 W=cm2) linearly polarized extreme ultraviolet laser pulse is studied by numerically solving the full-dimensional time-dependent Schr?dinger equation. For the laser intensities well beyond the perturbative limit, novel gridlike interference fringes are found in the correlated energy spectrum of the two photoelectrons. The interference can be traced to the multitude of two-electron wave packets emitted at different ionization times. A semianalytical model for the dressed two-photon double ionization is shown to qualitatively account for the interference patterns in the joint energy spectrum. Similar signatures of interferences between transient induced time-delayed ionization bursts are expected for other atomic and molecular multielectron systems.
关键词： strong-field ionization,two-electron interference,time-dependent Schr?dinger equation,double ionization,extreme ultraviolet laser pulse
更新于2025-09-19 17:13:59
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in a circularly polarized laser pulse
摘要： The dissociation of H2 + in a circularly polarized laser pulse is numerically studied by simulating the time-dependent Schr?dinger equation. After absorbing one or three photons, the nuclear wave packets carrying the angular momenta ˉh and 3 ˉh dissociate along the 2pσu state. Due to the broad initial kinetic-energy distribution of the superimposed nuclear vibrational states, the one-photon and three-photon dissociation pathways may end with the same kinetic energy. These coexisting dissociation pathways with same parities but different orbital angular momenta interfere with each other, resulting in the spiral nuclear momentum distribution in the laser polarization plane. The interference structure in the nuclear momentum distribution offers another freedom to identify the dissociation pathways of molecules in strong laser fields.
关键词： time-dependent Schr?dinger equation,photon dissociation pathways,circularly polarized laser pulse,spiral nuclear momentum distribution,H2 + dissociation
更新于2025-09-19 17:13:59
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Photoelectron holography from multiple-return backscattering electron orbits
摘要： We theoretically investigate the photoelectron momentum distributions of a diatomic molecule in a linearly polarized two-color laser ?eld by solving the time-dependent Schr?dinger equation. An upward curvature interference pattern is found in the two-dimensional photoelectron momentum spectra. Resorting to a simple semiclassical analysis and the strong-?eld approximation theory, we show that the interference pattern corresponds to a holographic pattern from the second-return backscattering electron orbits and, furthermore, the underlying physics of the distinct observation of such interference pattern is revealed. The holographic patterns from the backscattering electron orbits with the different return times may encode the information of the target structure at different times after ionization.
关键词： strong-?eld approximation theory,backscattering electron orbits,time-dependent Schr?dinger equation,photoelectron holography
更新于2025-09-16 10:30:52
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irradiated by a co-rotating two-color circularly polarized laser field
摘要： The high-order harmonic generation process of H2+ in a co-rotating two-color circularly polarized laser pulse was investigated by numerically solving the time-dependent Schr?dinger equation. Compared with the target of the atom, the harmonic intensity of H2+ is remarkably enhanced. Moreover, the harmonic intensity of H2+ approaches its maximum when the electric field amplitude ratio of the fundamental frequency and the second one is approximately 1:2.3. By analyzing the evolution of the time-dependent wave packets, the enhancement of harmonic intensity may be attributed to an increase in the probability of the ionized electron recolliding with the parent ion. In addition, the dependence of harmonic intensity on the internuclear distance and the alignment angle of H2+ is explored. We found that the ellipticity of the particular harmonic order changes with the molecular alignment angle, which provides a chance to generate an extreme ultraviolet coherent light pulse with controllable polarization.
关键词： time-dependent Schr?dinger equation,H2+,harmonic intensity,alignment angle,extreme ultraviolet coherent light pulse,controllable polarization,co-rotating two-color circularly polarized laser field,internuclear distance,high-order harmonic generation
更新于2025-09-12 10:27:22