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We perform a systematic analysis of quantum interference in nonsequential double ionization focusing on the recollision excitation with subsequent ionization (RESI) mechanism, employing the strong-field approximation (SFA). We find that interference has a major influence on the shape, localization, and symmetry of the correlated electron momentum distributions. In particular, the fourfold symmetry with regard to the parallel momentum components observed in previous SFA studies is broken. Two types of interference are observed and thoroughly analyzed, namely that caused by electron indistinguishability and intracycle events, and that stemming from different excitation channels. We find that interference is most prominent around the diagonal and antidiagonal in the parallel-momentum plane and provide fully analytical expressions for most interference patterns encountered. We also show that this interference can be controlled by an appropriate choice of phase and excited-state geometry. This leads a to myriad of shapes for the RESI distributions including correlated, anticorrelated, and ring shaped. [ABSTRACT FROM AUTHOR]

We investigate direct above-threshold ionization in diatomic molecules, with particular emphasis on how quantum interference is altered by a driving field of nonvanishing ellipticity. This interference may be either temporal, i.e., related to ionization events occurring at different times, or spatial, i.e., related to the electron emission at different centers in the molecule. Employing the strong-field approximation and saddle-point methods, we find that, in general, for nonvanishing ellipticity, there will be a blurring of the temporal and spatial interference patterns. The former blurring is caused by the electron velocity component perpendicular to the major polarization axis, while spatial interference is washed out as a consequence either of s-p mixing or of the temporal dependence of the ionization prefactor. Both types of interference are analyzed in detail in terms of electron trajectories, and specific conditions for which sharp fringes occur are provided. [ABSTRACT FROM AUTHOR]

We perform theoretical investigations of laser-induced nonsequential double ionization with few-cycle pulses, with particular emphasis on the dependence of the electron-momentum distributions on the carrier-envelope phase. We focus on the recollision-excitation with subsequent tunneling ionization (RESI) pathway,' in which a released electron, upon return to its parent ion, gives part of its kinetic energy to promote a second electron to an excited state. At a subsequent time, the second electron is freed through tunneling ionization. We show that the RESI electron-momentum distributions vary dramatically with regard to the carrier-envelope phase. By performing a detailed analysis of the dynamics of the two active electrons in terms of quantum orbits, we relate the shapes and the momentum regions populated by such distributions to the dominant set of orbits along which rescattering of the first electron and ionization of the second electron occurs. These orbits can be manipulated by varying the carrier-envelope phase. This opens a wide range of possibilities for controlling correlated attosecond electron emission by an adequate pulse choice. [ABSTRACT FROM AUTHOR]

We perform a detailed analysis of the importance of causality within the strong-field approximation and the steepest-descent framework for the recollision-excitation with subsequent tunneling ionization (RESI) pathway in laser-induced nonsequential double ionization (NSDI). In this time-delayed pathway, an electron returns to its parent ion and, by recolliding with the core, gives part of its kinetic energy to excite a second electron at a time t'. The second electron then reaches the continuum at a later time t by tunneling ionization. We show that, if t' and t are complex, the condition that recollision of the first electron occurs before tunnel ionization of the second electron translates into boundary conditions for the steepest-descent contours and thus puts constraints on the saddles to be taken when computing the RESI transition amplitudes. We also show that this generalized causality condition has a dramatic effect on the shapes of the RESI electron momentum distributions for few-cycle laser pulses. Physically, causality determines how the dominant sets of orbits of an electron returning to its parent ion can be combined with the dominant orbits of a second electron tunneling from an excited state. All features encountered are analyzed in terms of such orbits and their quantum interference. [ABSTRACT FROM AUTHOR]

We perform a detailed analysis of how the interplay between the residual binding potential and a strong laser field influences above-threshold ionization (ATI), employing a semianalytical, Coulomb-corrected strong-field approximation (SFA) in which the Coulomb potential is incoiporated in the electron propagation in the continuum. We find that the Coulomb interaction lifts the degeneracy of some SFA trajectories and we identify a set of orbits that, for high enough photoelectron energies, may be associated with rescattering. Furthermore, by performing a direct comparison with the standard SFA, we show that several features in the ATI spectra can be traced back to the influence of the Coulomb potential on different electron trajectories. These features include a decrease in the contrast, a shift towards lower energies in the interference substructure, and an overall increase in the photoelectron yield. All features encountered exhibit very good agreement with the ab initio solution of the time-dependent Schrodinger equation. [ABSTRACT FROM AUTHOR]

Using the recently developed Coulomb quantum orbit strong-field approximation, we perform a systematic analysis of several features encountered in above-threshold ionization photoelectron angle-resolved distributions, such as side lobes and intra- and intercycle interference patterns. The latter include not only the well-known intracycle rings and the near-threshold fan-shaped structure, but also previously overlooked patterns. We provide a direct account of how the Coulomb potential distorts different types of interfering trajectories and changes the corresponding phase differences, and show that these patterns may be viewed as generalized holographic structures formed by up to three types of trajectories. We also derive analytical interference conditions and estimates valid in the presence or absence of the residual potential, and assess the range of validity of Coulomb-corrected interference conditions provided in the literature. [ABSTRACT FROM AUTHOR]