Quantum Kinetic Approach to Time-Resolved Photoionization of Atoms (original) (raw)
Physical Review A, 2010
The quantum regime of highly doubly excited states in two-electron atoms has, so far, been largely inaccessible both to numerical methods as well as to experiments. Recent advances in semiclassical closed orbit theory in combination with a quantum mapping approach have shown a new way into this region of high dynamical complexity. In particular, new scaling laws near the double-ionization threshold as well as the dominant semiclassical contributions to the total photoionization cross section can be identified. We will present this new approach here in all its detail. It is based on representing the photoionization cross section in terms of quantum maps. These quantum maps or quantum propagators are used as a starting point for developing an efficient numerical method for calculating cross sections. Furthermore, by writing the quantum operators in semiclassical approximations, it is possible to interpret the quantum results in terms of classical triple collision orbits and to derive threshold laws near the three-particle breakup point. Semiclassical and numerical quantum results show excellent agreement for a model system, namely collinear helium.
Laser-assisted photoionization: beyond the dipole approximation
Physical Review A, 2023
We present a theoretical study of atomic laser-assisted photoionization emission (LAPE) beyond the dipole approximation. By considering the non-relativistic non-dipole strong-field approximation (non-dipole Gordon-Volkov wave function), we analyze the different contributions to the photoelectron spectrum (PES), which can be written in terms of intra- and intercycle factors. We find that not only does our non-dipole approach exhibit asymmetric emission in the direction of light propagation, but also allows emission in dipole-forbidden directions. The former feature can be rooted both in intra- and intercycle interference processes, whilst the latter stems from a dependence of the sideband energy on the emission angle with respect to the propagation direction. Our theoretical scheme, presented here for He atoms in the 1s quantum state, is general enough to be applied to other atomic species and field configurations.
Physical Review A, 2006
A time-dependent approach for calculation of the triple differential cross section of sequential double photoionization of atoms by femto-and attosecond pulses is developed. The method involves the numerical solving of a system of coupled nonstationary Schrödinger equations which describe the inner-shell photoionization and the following Auger decay. The shape of the spectra and the angular distributions of photoelectrons are considered in the near-threshold region for the case of photoelectron-Auger electron coincidence experiments as well as for noncoincidence measurements. As examples, the cross sections for Ar͑2p͒ and Kr͑3d͒ sequential double photoionization are calculated and discussed. It is shown that the cross sections strongly depend on the duration of the ionizing pulse. In contrast, the asymmetry parameters, characterizing the angular distribution of photoelectrons, are practically independent of the characteristics of the pulse.
Physical Review A, 1997
Radiation conditions are introduced as an exact method to truncate numerical solutions of the timedependent Schrödinger-equation at the boundaries of the numerical grid. A rigorous derivation of radiation conditions is given by the Green-function method for one-and three-dimensional regions. An accurate finitedifference representation is obtained for a one-dimensional region. The method is applied to calculations of strong-field photoionization. The calculation of ionization probabilities and energy spectra by the truncated solution is illustrated. ͓S1050-2947͑97͒06107-6͔
Photoionization of Helium Atoms through a Superposition of Higher Harmonics
Acta Physica Hungarica A) Heavy Ion Physics, 2006
We present a coupled-channel calculation of two-photon single ionization of helium by a superposition of the 7th to the 13th harmonic of a Ti:sapphire laser. Solving the time-dependent two-electron Schrödinger equation with a coherent polychromatic field, the single-ionization probabilities are calculated. Besides Slater-like orbitals we use regular Coulomb wavepackets in our configurational interaction basis to describe the single-and double-electron continuum. Linearly polarized laser pulses are used in the length gauge within the dipole approximation. We applied cosines squared normalized envelope functions. The pulse intensity is varied between 10 9 and 10 12 W/cm 2 , the total duration of each harmonics is between 36-49 femtoseconds. Our results are compared to other ab initio calculations, the possible reasons of the discrepancies are discussed.
Theory of inner-shell photoionization of fixed-in-space molecules
Physical Review A, 2001
A theory is presented for the calculation of molecular inner-shell photoionization near thresholds and electron-molecular-ion elastic scattering. The interaction of the incoming/outgoing electron with each atom of the formation ͑except for the ionized atom͒ is accounted for by suitable boundary conditions imposed on the electron wave function at nuclei of these atoms in the system. The theory is applied to calculations of the form of the photoelectron angular distribution for 1s photoionization of the C atom in the CO diatomic molecule, as well as for the photoelectron angular distribution due to photodetachment from a quasimolecular negative ion consisting of a C Ϫ ion located near a neutral O atom.
Multicentered Theory of Molecular Photoionization
Surface Review and Letters, 2002
A new theory for near-threshold photoionization of inner electrons of atoms confined in multicentered atomic formations, e.g. molecules or clusters, is developed. The formulas for fixed-in-space molecules have been derived. The interaction of the photoelectron in the continuum with atoms that surround the atom being ionized, is replaced by the suitable boundary conditions imposed on the photoelectron wave function at the location of nuclei of these atoms in the molecule. The general formulas derived are used to calculate photoelectron angular distributions of diatomic molecules. The calculated data are in qualitative agreement with experimental data and results of other calculations.
Photoionization dynamics from : a one-electron model
Chemical Physics Letters, 2004
Quantum dynamics of photoionization from Cl À 2 is investigated by constructing a purely one-electron model Hamiltonian of the anion calibrated with the help of ab initio theoretical calculations at the MRSD-CI level. A mean-field time-dependent Fourier grid Hamiltonian method is used to investigate the modulation of the dynamics of photoionization from Cl À 2 caused by the coupling of electronic and nuclear motions. Vibrational quenching at low coupling strength is predicted to turn into vibrational enhancement of ionization at higher strengths of coupling.
Journal of Physics: Conference Series, 2014
We study the photoionization and autoionization of Helium atom subject to ultrashort laser pulses by using a Feshbach formalism in the time domain. We solve the time-dependent Schrödinger equation in terms of a configuration interaction (CI) spectral method, in which the total wavefunction is expanded with configurations defined within bound-like (Q) and scattering-like (P) halfspaces. The method allows one to provide accurate descriptions of both the atomic structure (energy positions and widths) and the photodynamics. We illustrate our approach by i) calculating the time-resolved one-photon ionization below the He + (n=2) ionization threshold, from 1 1 S e and 2 1 P o initial states, then reaching the lowest autoionizing states of 1 S e , 1 P o and 1 D e final symmetries ii) studing the temporal formation of the Fano profile of 1 P o resonances and iii) showing its performance in obtaining the perturbative long-time limit of one-and two-photon ionization cross sections using ultrashort laser pulses following a recently developed procedure in Phys. Rev. A, 77, 032716 (2008).
Controlled strong non-dipole effects in photoionization of confined atoms
Journal of Physics B: Atomic, Molecular and Optical Physics, 2000
It is demonstrated that non-dipole effects in low energy photoionization of atoms surrounded by a repulsive semi-transparent potential can be increased by many orders of magnitude due to virtual levels occuring in the spectra of photoelectrons as a result of confinement. The strengths, widths and positions of such resonances in non-dipole channels can be controlled by altering the characteristics of the confining potential, and under certain circumstances can be so large that treating quadrupole transitions as a perturbation breaks down, even for photon energies as low as tens of eV. Our conclusions have relevance to the interpretation of non-dipole photoemission spectra from solids, molecules, atoms trapped inside fullerene molecules, quantum dots, etc. Non-dipole electric-dipole-electric-quadrupole (E1-E2) interference effects in angular distribution spectra of photoelectrons due to photoionization of free atoms have attracted much attention in recent years, both from theorists (