arXiv subjects

Francois Mauger

Publications and source records attributed to Francois Mauger.

27 records · Page 2Linked to original sources

arXiv2012

Delayed double ionization as a signature of Hamiltonian chaos

We analyze the dynamical processes behind delayed double ionization of atoms subjected to strong laser pulses. Using reduced models, we show that these processes are a signature of Hamiltonian chaos which results from the competition between the laser field and the Coulomb attraction to the nucleus. In particular, we exhibit the paramount role of the unstable manifold of selected periodic orbits which lead to a delay in these double ionizations. Among delayed double ionizations, we consider the case of "Recollision Excitation with Subsequent Ionization" (RESI) and, as a hallmark of this mechanism, we predict oscillations in the ratio of RESI to double ionization yields versus laser intensity. We discuss the significance of the dimensionality of the reduced models for the analysis of the dynamical processes behind delayed double ionization.

physics.atom-ph↗

arXiv2011

Annular billiard dynamics in a circularly polarized strong laser field

We analyze the dynamics of a valence electron of the buckminsterfullerene molecule (C60) subjected to a circularly polarized laser field by modeling it with the motion of a classical particle in an annular billiard. We show that the phase space of the billiard model gives rise to three distinct trajectories: "Whispering gallery orbits", which only hit the outer billiard wall, "daisy orbits" which hit both billiard walls (while rotating solely clockwise or counterclockwise for all time), and orbits which only visit the downfield part of the billiard, as measured relative to the laser term. These trajectories, in general, maintain their distinct features, even as intensity is increased from 10^10 to 10^14 W*cm^-2. We attribute this robust separation of phase space to the existence of twistless tori.

physics.atom-ph↗

arXiv2011

Mechanism of delayed double ionization in a strong laser field

When intense laser pulses release correlated electrons, the time delay between the ionizations may last more than one laser cycle. We show that this "Recollision-Excitation with Subsequent Ionization" pathway originates from the inner electron being promoted to a sticky region by a recollision where it is trapped for a long time before ionizing. We identify the mechanism which regulates this region, and predict oscillations in the double ionization yield with laser intensity.

physics.atom-ph↗

arXiv2010

Controlling double ionization of atoms in intense bichromatic laser pulses

We consider the classical dynamics of a two-electron system subjected to an intense bichromatic linearly polarized laser pulse. By varying the parameters of the field, such as the phase lag and the relative amplitude between the two colors of the field, we observe several trends from the statistical analysis of a large ensemble of trajectories initially in the ground state energy of the helium atom: High sensitivity of the sequential double ionization component, low sensitivity of the intensities where nonsequential double ionization occurs while the corresponding yields can vary drastically. All these trends hold irrespective of which parameter is varied: the phase lag or the relative amplitude. We rationalize these observations by an analysis of the phase space structures which drive the dynamics of this system and determine the extent of double ionization. These trends turn out to be mainly regulated by the dynamics of the inner electron.

nlin.CD↗

arXiv2010

Simulated annealing algorithm for finding periodic orbits of multi-electron atomic systems

We adapt the simulated annealing algorithm to the search of periodic orbits for classical multi-electron atomic systems. This is done by minimizing the n-th return distance to the initial position on a Poincare surface of section under an energy constraint. Here we give evidence of the feasibility of the method by applying it to the helium atom in the ground state for one to three spatial dimensions. We examine the structure of the dynamics and connect its organization to the periodic orbits we have found.

physics.atom-ph↗

arXiv2010

Nonlinear dynamics of recollisions in the double ionization processes of atoms in strong fields

Double ionization processes triggered by intense linearly polarized laser fields have revealed the paramount role of electron-electron collisions. It has been shown that the correlated dynamics of such electronic collisions can be modeled by a two dimensional symplectic map which captures the bare essentials of the energy exchange processes occurring during a recollision between the two electrons. We investigate linear and nonlinear properties of this map and connect them to the dynamical organization of phase space and related statistical data

physics.atom-ph↗

arXiv2010

Dynamics of recollisions for the double ionization of atoms in intense laser fields

We investigate the dynamics of electron-electron recollisions in the double ionization of atoms in strong laser fields. The statistics of recollisions can be reformulated in terms of an area-preserving map from the observation that the outer electron is driven by the laser field to kick the remaining core electrons periodically. The phase portraits of this map reveals the dynamics of these recollisions in terms of their probability and efficiency.

physics.atom-ph↗

arXiv2010

Recollisions and correlated double ionization with circularly polarized light

It is generally believed that the recollision mechanism of atomic nonsequential double ionization is suppressed in circularly polarized laser fields because the returning electron is unlikely to encounter the core. On the contrary, we find that recollision can and does significantly enhance double ionization, even to the extent of forming a "knee", the signature of the nonsequential process. Using a classical model, we explain two apparently contradictory experiments, the absence of a knee for helium and its presence for magnesium.

physics.atom-ph↗

arXiv2009

From recollisions to the knee: A road map for double ionization in intense laser fields

We examine the nature and statistical properties of electron-electron collisions in the recollision process in a strong laser field. The separation of the double ionization yield into sequential and nonsequential components leads to a bell-shaped curve for the nonsequential probability and a monotonically rising one for the sequential process. We identify key features of the nonsequential process and connect our findings in a simplified model which reproduces the knee shape for the probability of double ionization with laser intensity and associated trends.

physics.atom-ph↗