Coulomb effects in the dipole and nondipole regimes of strong-field ionization

Due to recent advancements in measurement precision and in laser field generation techniques, new phenomena were observed in strong-field ionization physics. It appeared that the explanation of new phenomena were based on the previously unidentified Coulomb field effects of the atomic core on the ionized electron, and on the interrelations of the Coulomb field and nondipole effects. The aim of this thesis is two fold. Firstly, we develop analytical methods for more accurate description of the strong-field ionization process, which is based on a more accurate treatment of the electron dynamics in the laser and Coulomb field of the atomic core, with an emphasize on nondipole effects. Secondly, we apply the developed analytical methods, along with the common theoretical machinery of strong-field physics, for explanation of the results of recent and ongoing experiments devoted to the interplay of the Coulomb and nondipole effects in strong-field ionization process in mid-infrared laser fields of linear and elliptical polarization, as well as for extension of the strong-field holography technique into the nondipole regime. Within the first aim, we advance the quantum theory of the Coulomb-corrected strongfield approximation, calculating the high-order correction terms to the electron continuum wave function in the laser and Coulomb fields using the eikonal-Volkov approximation and describe nonadiabatic momentum shifts for photoelectrons. Further, we develop a classical theory for the description of multiple recollisions of the ionized electron with the atomic core, which is the basis for understanding of the, so-called, Coulomb focusing phenomenon. The key point is a restriction of the interaction to well specified and defined rescattering points along the electron classical trajectory, which leads to analytical estimates for the momentum transfer at these points and, subsequently, for the total momentum transfer to any electron tunneled at any arbitrary phase of the laser field. Although, the Coulomb field is treated as a perturbation near each scattering point, it appears to disturb the global dynamics significantly via multiple recollisions. The derived analytical formulas for the Coulomb momentum transfer of the classical theory are employed to gain a deeper insight into the features of Coulomb focusing in different field configurations. In particular, we provide an explanation and scaling for the counterintuitive negative shift of the Coulomb focusing cusp in a recent experiment with a linearly polarized mid-infrared laser field, and show its dependence on the photoelectron energy. Further, we explain the appearance of the sharp ridge of low-energy electrons in the experimental photoelectron momentum distribution in an elliptically polarized laser field, and show how it is related to the shift of photoelectron momentum distribution against the laser propagation direction due to nondipole effects. Finally, we give an interpretation of the experimental results on strong-field photoelectron holography in the nondipole regime. We employ three different theoretical techniques for calculation of interference patterns: Coulomb-corrected strong-field approximation, Quantum-Trajectory Monte Carlo simulations and Simple-man’s three-step model, and provide a description of the nondipole features of the interference fringes. We analyze the signature of atomic species for the interferometric holography pattern in the photoelectron distribution, discussing the cases of a xenon atom and an O₂ molecule