The scattering of an ultrashort electromagnetic pulse by atomic particles is described using a consistent quantum-mechanical approach taking into account excitation of a target and nondipole electromagnetic interaction, which is valid in a broad spectral range. This approach is applied to the scattering of single- and few-cycle pulses by a multielectron atom and a hydrogen atom. Scattering spectra are obtained for ultrashort pulses of different durations. The relative contribution of “elastic” scattering of a single-cycle pulse by a hydrogen atom is studied in the high-frequency limit as a function of the carrier frequency and scattering angle.

The excitation of a two-level system by a chirped laser pulse is analyzed using an analytical approach (in the perturbation-theory limit) that involves the modified rotating-wave approximation and the numerical solution to the Bloch equation. The dependence of the population of the upper energy level on the chirp is studied for various radiation intensities and pulse durations. An exact solution is compared with the result obtained using the modified rotating-wave approximation and the perturbation theory. It is demonstrated that, for a certain range of parameters, the excitation probability of a two-level system can be effectively controlled via a variation in the chirp.

Statistical models combined with the local plasma frequency approach applied to the atomic electron density are employed to study the photoionization cross-section for complex atoms. It is demonstrated that the Thomas–Fermi atom provides surprisingly good overall agreement even for complex outer-shell configurations, where quantum mechanical approaches that include electron correlations are exceedingly difficult. Quantum mechanical photoionization calculations are studied with respect to energy and nl quantum number for hydrogen-like and non-hydrogen-like atoms and ions. A generalized scaled photoionization model (GSPM) based on the simultaneous introduction of effective charges for non-H-like energies and scaling charges for the reduced energy scale allows the development of analytical formulas for all states nl. Explicit expressions for nl = 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, and 5s are obtained. Application to H-like and non-H-like atoms and ions and to neutral atoms demonstrates the universality of the scaled analytical approach including inner-shell photoionization. Likewise, GSPM describes the near-threshold behavior and high-energy asymptotes well. Finally, we discuss the various models and the correspondence principle along with experimental data and with respect to a good compromise between generality and precision. The results are also relevant to large-scale integrated light–matter interaction simulations, e.g., X-ray free-electron laser interactions with matter or photoionization driven by a broadband radiation field such as Planckian radiation.

The possibility of the phase control for the excitation of a quantum system in the discrete spectrum under the action of a short high-intensity laser pulse with a controlled phase is theoretically analyzed. The analysis is performed using the example of the simplest two-level system (TLS) employing a numerical solution to equations for the optical Bloch vector. It is demonstrated that the excitation probability and the mean dipole moment of the quantum system, which determine the normal luminescence and the superradiance in the TLS ensemble, respectively, substantially depend on the phase of the laser pulse for relatively short and powerful laser pulses.

The dynamics of photoexcitation of the hydrogen atom in the discrete and continuous spectra under the action of laser pulses in the attosecond range of time and pulse durations has been analyzed using perturbation theory. It is shown that over time interval shorter than or on the order of pulse duration, the time dependence of the photoexcitation probability is generally oscillating by nature. It has been established that for certain values of parameters, the envelope of this dependence has a peak, the position of which is determined by the pulse duration and carrier frequency.

Novel phenomena and methods related to dielectronic capture and dielectronic recombination are studied for non-local thermodynamic equilibrium (LTE) plasmas and for applications to non-LTE ionization balance. It is demonstrated that multichannel autoionization and radiative decay strongly suppress higher-order contributions to the total dielectronic recombination rates, which are overestimated by standard approaches by orders of magnitude. Excited-state coupling of dielectronic capture is shown to be much more important than ground-state contributions, and electron collisional excitation is also identified as a mechanism driving effective dielectronic recombination. A theoretical description of the effect of angular-momentum-changing collisions on dielectronic recombination is developed from an atomic kinetic point of view and is visualized with a simple analytical model. The perturbation of the autoionizing states due to electric fields is discussed with respect to ionization potential depression and perturbation of symmetry properties of autoionization matrix elements. The first steps in the development of statistical methods are presented and are realized in the framework of a local plasma frequency approach. Finally, the impact of collisional–radiative processes and atomic population kinetics on dielectronic recombination is critically discussed, and simple analytical formulas are presented.