Intense-field many-body S-matrix theory (IMST) provides a systematic ab initio approach to investigate the dynamics of atoms and molecules interacting with intense laser radiation. We review the derivation of IMST as well as its diagrammatic representation and point out its advantage over the conventional 'prior' and 'post' expansions which are shown to be special cases of IMST. The practicality and usefulness of the theory is illustrated by its application to a number of current problems of atomic and molecular ionization in intense fields. We also present a consistent S-matrix formulation of the quantum amplitude for high harmonic generation (HHG) and point out some of the most general properties of HHG radiation emitted by a single atom as well as its relation to coherent emission from many atoms. Experimental results for single and double (multiple) ionization of atoms and the observed distributions of coincidence measurements are analysed and the dominant mechanisms behind them are discussed. Ionization of more complex systems such as diatomic and polyatomic molecules in intense laser fields is analysed as well using IMST and the results are discussed with special attention to the role of molecular orbital symmetry and molecular orientation in space. The review ends with a summary and a brief outlook.

https://iopscience.iop.org/article/10.1088/0953-4075/38/3/R01/pdf

Intense-field many-body S-matrix theory

Atomic negative ions: structure, dynamics and collisions

In a recombining plasma the metastable states are known to accumulate population thereby slowing down the recombination process. We show that an account of the doubly excited autoionizing states, formed due to collisional recombination of metastable ions, results in a significant acceleration of recombination. A fully time-dependent collisional-radiative (CR) modeling for stripped ions of carbon recombining in a cold dense plasma demonstrates an order of magnitude faster recombination of He-like ions. The CR model used in calculations is discussed in detail.

/pdf/accelerated-recombination-due-to-resonant-deexcitation-of-1f85genuzf.pdf

Accelerated recombination due to resonant deexcitation of metastable states

To understand what happens when biological matter is irradiated needs a detailed knowledge of the microscopic distribution of interactions and especially of the energy deposited in irradiated matter. Monte Carlo event-by-event simulations are particularly suitable for this task. However, the development of these track-structure codes necessitates accurate interaction cross sections for all the electronic processes: ionization, excitation and elastic scattering. In these conditions, we have recently developed a Monte Carlo code for electrons in water, this latter being commonly used to simulate the biological medium. All the electronic processes are studied in detail via theoretical differential and total cross-section calculations. The purpose of this work is to make an inter-comparison of our cross sections with those used in the electron track-structure codes developed in the literature, and to compare macroscopic quantities such as stopping powers and mean energy transfer distributions to available experimental data and/or to theoretical predictions in liquid water.

Theoretical cross sections for electron collisions in water: structure of electron tracks.

Semiempirical formulae for multiple-ionization (MI) cross sections sigma n of atoms and ions by electron impact are suggested for ejection three or more electrons n>or=3. The formulae have been deduced on the basis of available experimental data on sigma n and the assumption of the Born-Bethe dependence of sigma n on the incident electron energy E. The formulae suggested can be used for estimation of MI cross sections sigma n, n>or=3, from threshold up to high electron energies E approximately=105 eV for an arbitrary atomic or ionic target.

Semiempirical formulae for multiple ionization of neutral atoms and positive ions by electron impact

On the basis of average experimental data we demonstrate scaling laws of electron-impact multiple ionization cross sections and propose expressions for the cross sections for arbitrary atoms and ions.

A scaling of multiple ionization cross sections

We present an easy to use expression for cross sections of electron-impact-induced 1s{sup 2}nl{r_arrow}1s{sup 2}n{sup {prime}}l{sup {prime}} excitation transitions with 2{le}n{le}n{sup {prime}}{le}4 in multiply charged ions of lithium isoelectronic sequence. This expression is based on our computations by convergent close-coupling (CCC) and Coulomb-Born with exchange and normalization (CBE) methods. We show scaling of the CCC and CBE cross sections with atomic number Z and use this scaling for presentation of the cross-section data. For 6{le}Z{le}30 the scaling is accurate to better than {plus_minus}20{percent} at any energy except in the vicinity of resonances. Contributions from indirect excitation channels do not scale with Z; however, for calculation of excitation rates it is enough to average locally these contributions over energy and to take them into account in a frame of a general scaling-based expression for the cross sections. For excitation rates, total inaccuracy caused by all simplifications in the cross-section presentation is likely to be less than {plus_minus}30{percent} even for most risky cases. This assessment is based on comparison of excitation rates, computed using our scaling-based expression for the cross sections, with the excitation rates, computed using high-resolution (CCC and R matrix) cross sections and experimental data. {copyright} {ital 1997} {ital Themore » American Physical Society}« less

https://plasma-gate.weizmann.ac.il/Pubs/praat97.pdf

A. Goldgirsh

Papers

A scaling of multiple ionization cross sections

Electron-impact-excitation cross sections of lithiumlike ions