arXiv subjects

Dmitry K. Efimov

Publications and source records attributed to Dmitry K. Efimov.

11 recordsLinked to original sources

arXiv2026

Restricted-Geometry Quantum Models Beyond Atoms: Application of the Eckhardt-Sacha approach to NSDI in Diatomic Systems

We present a (1+1)-dimensional quantum model designed to describe nonsequential double ionization (NSDI) in homonuclear diatomic molecules exposed to strong linearly polarized laser fields. Extending the restricted-geometry framework previously developed for atomic systems by Eckhardt and Sacha, our approach captures key features of NSDI, including the characteristic knee structure in double ionization yields. Despite its simplifying assumptions, the model shows good agreement with experimental data and proves particularly suitable for systems with $σ$-type orbital symmetry. It offers a computationally efficient tool for exploring multi-electron dynamics in molecular systems.

physics.atom-ph↗

arXiv2024

Quantum versus semi-classical signatures of correlated triple ionization in Dalitz plots

We investigate correlated three-electron escape in Ne when driven by an intense, infrared laser field. We do so by employing a reduced-dimensionality quantum-mechanical model and two three-dimensional semi-classical models. One semi-classical model is a recently developed one that accounts with effective coulomb potentials for the interaction between two bound electrons (ECBB) while it fully accounts for all other interactions. The other semi-classical model is the Heisenberg one, which effectively accounts for the interaction of each electron with the core via a soft-core potential. We identify and compare the signatures of correlated three-electron escape for both quantum and semi-classical models on Dalitz plots and find a better agreement between the quantum and the ECBB model. We also show that a central ``spot'' on the Dalitz plots is reproduced by all models. Using the ECBB model we associate this ``spot'' with the direct triple ionization pathway and argue this to be the case also for the quantum model. Devising a simple classical model that accounts for the direct pathway of triple ionization, we show that the width of this spot in the Dalitz plots solely depends on the time of tunnel-ionization.

physics.atom-ph↗

arXiv2023

Hyperfine interaction in the Autler-Townes effect II: control of two-photon selection rules in the Morris-Shore basis

We investigated the absence of certain bright peaks in Autler-Townes laser excitation spectra of alkali metal atoms. Our research revealed that these dips in the spectra are caused by a specific architecture of adiabatic (or ``laser-dressed'') states in hyperfine (HF) components. The dressed states' analysis pinpointed several cases where constructive and destructive interference between HF excitation pathways in a two-photon excitation scheme limits the available two-photon transitions. This results in a reduction of the conventional two-photon selection rule for the total angular momentum $F$, from $ΔF= 0,\pm 1$ to $ΔF\equiv 0$. Our discovery presents practical methods for selectively controlling the populations of unresolvable HF $F$-components of $ns_{1/2}$ Rydberg states in alkali metal atoms. Using numerical simulations with sodium and rubidium atoms, we demonstrate that by blocking the effects of HF interaction with a specially tuned auxiliary control laser field, the deviations from the ideal selectivity of the HF components population can be lower than $0.01\%$ for Na and $0.001\%$ for Rb atoms.

physics.atom-ph↗

arXiv2023

Strong-Field Double Ionization in a Three-Electron Atom: Momentum Distribution Analysis

We study strong-field double ionization in a three-electron atom by applying a simplified, reduced-dimensionality model with three active electrons. The influence of the spin-induced symmetry of the spatial part of the wavefunction on the final two-photoectron momentum distribution is discussed. We identify partial momentum distributions originating from different sets of spins of outgoing electrons providing in this way a quantum support connection between V-structure and direct ionization typically explained classically. Changes in the momentum distribution with increasing field amplitude obtained in our simplified model are shown to be well-correlated with experimental data known from the literature. The possible relation between the observed dependencies and different ionization mechanisms is discussed.

physics.atom-ph↗

arXiv2022

A systematic construction of Gaussian basis sets for the description of laser field ionization and high-harmonic generation

A precise understanding of mechanisms governing the dynamics of electrons in atoms and molecules subjected to intense laser fields has a key importance for the description of attosecond processes such as the high-harmonic generation and ionization. From the theoretical point of view, this is still a challenging task, as new approaches to solve the time-dependent Schrödinger equation with both good accuracy and efficiency are still emerging. Until recently, the purely numerical methods of real-time propagation of the wavefunction using finite grids have been frequently and successfully used to capture the electron dynamics in small one- or two-electron systems. However, as the main focus of attoscience shifts toward many-electron systems, such techniques are no longer effective and need to be replaced by more approximate but computationally efficient ones. In this paper, we explore the increasingly popular method of expanding the wavefunction of the examined system into a linear combination of atomic orbitals and present a novel systematic scheme for constructing an optimal Gaussian basis set suitable for the description of excited and continuum atomic or molecular states. We analyze the performance of the proposed basis sets by carrying out a series of time-dependent configuration interaction calculations for the hydrogen atom in fields of intensity varying from $5 \times 10^{13}\:\rm W/cm^2$ to $5 \times 10^{14}\:\rm W/cm^2$. We also compare the results with the data obtained using Gaussian basis sets proposed previously by other authors.

physics.chem-ph↗

arXiv2021

Strong-field triple ionization of atoms with $p^3$ valence shell

The interaction of strong pulsed femtosecond laser field with atoms having three equivalent electrons in the outer shell ($p^3$ configuration, e.g. nitrogen) is studied via numerical integration of a time-dependent Schrödinger equation on a grid approach. Single, double and triple ionization yields originating from a completely antisymmetric wave function are calculated and extracted using a restricted-geometry model with the soft-core potential and three active electrons. The direct triple ionization channel is found to produce a larger yield than the channel connected with single and then direct double ionization. Compared against earlier results investigating the $n s^ 2 n p^1$ configuration, we propose that the differences found here might in fact be accessible through electron's momentum distribution.

physics.atom-ph↗

arXiv2020

Symphony on Strong Field Approximation

This paper has been prepared by the Symphony collaboration (University of Warsaw, Uniwersytet Jagielloński, DESY/CNR and ICFO) on the occasion of the 25th anniversary of the "simple man's models" which underlie most of the phenomena that occur when intense ultrashort laser pulses interact with matter. The phenomena in question include High-Harmonic Generation, Above-Threshold Ionization, and Non-Sequential Multielectron Ionization. "Simple man's models" provide, both an intuitive basis for understanding the numerical solutions of the time-dependent Schrödinger equation, and the motivation for the powerful analytic approximations generally known as the Strong Field Approximation (SFA). In this paper we first review the SFA in the form developed by us in the last 25 years. In this approach SFA is a method to solve the TDSE using a systematic perturbation theory in a part of the Hamiltonian describing continuum-continuum transitions in the presence of the laser field. In this review we focus on recent applications of SFA to HHG, ATI and NSMI from multi-electron atoms and from multi-atom. The main novel part of the presented theory concerns generalizations of SFA to: (i) time-dependent treatment of two-electron atoms, allowing for studies of an interplay between Electron Impact Ionization (EII) and Resonant Excitation with Subsequent Ionization (RESI); (ii) time-dependent treatment in the single active electron (SAE) approximation of "large" molecules and targets which are themselves undergoing dynamics during the HHG or ATI process. In particular, we formulate the general expressions for the case of arbitrary molecules, combining input from quantum chemistry and quantum dynamics. We formulate also theory of time-dependent separable molecular potentials to model analytically the dynamics of realistic electronic wave packets for molecules in strong laser fields.

quant-ph↗

arXiv2020

Strong-field ionization of atoms with $p^3$ valence shell: Two versus three active electrons

For a model atom with the $p^3$ valence shell we construct consistent three- and two-active electrons models enabling their direct comparison. Within these models, we study the influence of the third active electron on the double ionization yield in strong femtosecond laser fields. We reveal proportionality between double ionization signals obtained with both models in the field intensity region where non-sequential ionization dominates. We derive analytically a correspondence rule connecting the double ionization yields obtained within the three- and two-active electrons models.

physics.atom-ph↗

arXiv2020

Ab initio study of time-dependent dynamics in strong-field triple ionization

An ab initio analysis of strong-field three-electron ionization in a restricted-dimensionality model reveals the dynamics of the ionization process and the dominant channels for double (DI) and triple ionization (TI). Simulations using wave functions that respect the Pauli principle show that the most likely channel is a sequence of single ionization (SI) and DI, while direct TI has a much lower probability. The dominant DI process has the highest probability for a singlet of up- and down-spin electrons. The results demonstrate the significance of the Pauli principle for the selection of dominant pathways in ionization and possibly other many-electron processes in strong fields.

physics.atom-ph↗

arXiv2019

Double ionization of a three-electron atom: Spin correlation effects

We study the effects of spin degrees of freedom and wave function symmetries on double ionization in three-electron systems. Each electron is assigned one spatial degree of freedom. The resulting three-dimensional Schrödinger equation is integrated numerically using grid-based Fourier transforms. We reveal three-electron effects on the double ionization yield by comparing signals for different ionization channels. We explain our findings by the existence of fundamental differences between three-electronic and truly two-electronic spin-resolved ionization schemes. We find, for instance, that double ionization from a three-electron system is dominated by electrons that have the opposite spin.

physics.atom-ph↗

arXiv2018

Restricted space ab initio models for double ionization by strong laser pulses

Double electron ionisation process occurs when an intense laser pulse interacts with atoms or molecules. Exact {\it ab initio} numerical simulation of such a situation is extremely computer resources demanding, thus often one is forced to apply reduced dimensionality models to get insight into the physics of the process. The performance of several algorithms for simulating double electron ionization by strong femtosecond laser pulses are studied. The obtained ionization yields and the momentum distributions of the released electrons are compared, and the effects of the model dimensionality on the ionization dynamics discussed.

physics.atom-ph↗