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Photoelectron Momentum Distributions of Single-Photon Ionization under a Pair of Elliptically Polarized Attosecond Laser Pulses
摘要： The attosecond ionization dynamics of atoms has attracted extensive attention during these days. However, the role of the initial state is not clearly understood. To address this question, we perform simulations on the neon atom and its model atom with different initial states by numerically solving the corresponding two-dimensional time-dependent Schr?dinger equations. We theoretically investigate atomic photoelectron momentum distributions (PMDs) by a pair of elliptically polarized attosecond laser pulses. We find that the PMD is sensitive not only to the ellipticities of the pulses, the relative helicity and time delay of the pulses, but also to the symmetry of the initial electronic states. Results are analyzed by the first-order time-dependent perturbation theory (TDPT) and offer a new tool for detecting the rotation direction of the ring currents.
关键词： photoelectron momentum distributions,elliptically polarized attosecond laser pulses,magnetic quantum numbers,the rotation direction of the ring currents
更新于2025-09-23 15:21:01
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Pulse-length effects in strong-field ionization of atoms by co-rotating and counter-rotating bicircular laser pulses
摘要： We study strong-?eld ionization of H and selected rare-gas atoms by solving the three-dimensional time-dependent Schr?dinger equation in the single-active-electron approximation with particular attention to the effect of pulse length on the total ionization yields (TIYs) produced by counter-rotating bicircular (CRBC) lasers compared to co-rotating bicircular (COBC) lasers. To this end, TIYs, photoelectron momentum distributions, and above-threshold ionization spectra are presented for various pulse durations and peak intensities. For pulses containing ?ve or more cycles of the fundamental near-infrared laser ?eld, the CRBC/COBC ratio of TIYs is affected due to ionization via excited states and multiphoton ionization channels. For pulses containing less than ?ve cycles, the CRBC/COBC ratio of TIYs depends on both the frequency combination and number of optical cycles: With the 1ω-2ω frequency combination, the ratio of TIYs is enhanced (reduced) for pulses with an odd (even) number of optical cycles. The 1ω-3ω frequency combination was considered for pulses containing two or three optical cycles, and for both pulse lengths the CRBC/COBC ratio of TIYs is less than unity.
关键词： photoelectron momentum distributions,bicircular laser pulses,time-dependent Schr?dinger equation,above-threshold ionization spectra,strong-?eld ionization
更新于2025-09-11 14:15:04
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-matrix-with-time-dependence theory for ultrafast atomic processes in arbitrary light fields
摘要： We describe an ab initio and nonperturbative R-matrix with time-dependence theory for ultrafast atomic processes in light fields of arbitrary polarization. The theory is applicable to complex, multielectron atoms and atomic ions subject to ultrashort (particularly few-femtosecond and attosecond) laser pulses with any given ellipticity, and it generalizes previous time-dependent R-matrix techniques restricted to linearly polarized fields. We discuss both the fundamental equations, required to propagate the multielectron wave function in time, as well as the computational developments necessary for their efficient numerical solution. To verify the accuracy of our approach, we investigate the two-photon ionization of He, irradiated by a pair of time-delayed, circularly polarized, femtosecond laser pulses, and compare photoelectron momentum distributions, in the polarization plane, with those obtained from recent time-dependent close-coupling calculations. The predictive capabilities of our approach are further demonstrated through a study of single-photon detachment from F? in a circularly polarized, femtosecond laser pulse, where the relative contribution of the co- and counter-rotating 2p electrons is quantified.
关键词： ultrafast atomic processes,R-matrix,circularly polarized laser pulses,single-photon detachment,time-dependence,photoelectron momentum distributions,arbitrary light fields,multielectron atoms
更新于2025-09-11 14:15:04
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High-order above-threshold ionization beyond the electric dipole approximation: Dependence on the atomic and molecular structure
摘要： We provide an in-depth analysis of high-order above-threshold ionization of atoms and molecules by strong laser pulses, using three different theoretical approaches beyond the electric dipole approximation: (i) the numerical solution of the time-dependent Schr?dinger equation, (ii) the classical three-step model, and (iii) the quantum-orbit model. In the classical and quantum-orbit models, we include an accurate description of the rescattering step by target-specific differential scattering cross sections. The considerable forward shift of the photoelectron momentum distributions along the laser propagation direction can be understood in terms of the nondipole electron motion after rescattering. An explanation of the additionally observed forward-backward asymmetry of the signal strength requires the accurate modeling of the rescattering step and the electron dynamics before the rescattering event. For the H2+ molecular ion, we compare the cases of parallel and perpendicular alignment of the molecular axis and we show that the interference pattern and its modification due to the nondipole effects are orientation dependent. Compared to atoms, the nondipole effects in molecular high-order above-threshold ionization appear more pronounced and amenable to experimental observation.
关键词： high-order above-threshold ionization,nondipole effects,photoelectron momentum distributions,quantum-orbit model,classical three-step model,H2+ molecular ion,electric dipole approximation,time-dependent Schr?dinger equation
更新于2025-09-04 15:30:14