Dispersion in laser-driven relativistic quantum systems

The wave packet dynamics of electrons driven by strong laser fields is examined with the objective to both describe and manipulate the spreading dynamics. Having established analytical methods based on either classical or quantum mechanics, the quantum approach is first applied to free, laser-driven electrons. Intuitive results are found for both the relativistic and the nonrelativistic regime beyond the dipole approximation. In order to generalize the concept of recollisions to relativistic energies where magnetic field effects are important, the electron dynamics in standing laser fields with linear and circular polarization are analyzed and compared. Furthermore, a novel scheme of two consecutive laser pulses is introduced, which allows for recollisions with the maximum electron energy accessible in propagating laser fields. In this scheme, the Lorentz drift is employed both to separate electrons from atoms or molecules and to drive them back for recollisions. Aiming to increase the reaction probabilities of recollisions, two methods to inverse wave packet spreading are introduced. Both approaches, i.e. refocusing with a harmonic potential and magnetic refocusing, can be implemented in the scheme with two consecutive laser pulses to enable effective, relativistic recollisions

Laser-induced nonresonant nuclear excitation in muonic atoms

Coherent nuclear excitation in strongly laser-driven muonic atoms is calculated. The nuclear transition is caused by the time-dependent Coulomb field of the oscillating charge density of the bound muon. A closed-form analytical expression for electric multipole transitions is derived and applied to various isotopes; the excitation probabilities are in general very small. We compare the process with other nuclear excitation mechanisms through coupling with atomic shells and discuss the prospects to observe it in experiment.Comment: 7 pages, 5 figure

Refocussed relativistic recollisions

It is demonstrated that a magnetic field pulse can be applied to refocus a spreading electron wave packet in a relativistic recollision scheme. The drift due to the Lorentz force occurring in strong laser fields is employed to separate an electron from the core. Before it is driven back for recollision by a second counter-propagating laser pulse, the dynamics of wave packet spreading is reversed by a magnetic field pulse. At the instant of recollision, the electron wave packet is refocussed to small spatial widths while it holds maximal kinetic energy. This way, efficient recollisions are shown to occur up to the high-energy regime

Relativistic classical and quantum dynamics in intense crossed laser beams of various polarizations

The dynamics of an electron in crossed laser fields is investigated analytically. Two different standing wave configurations are compared. The counterpropagating laser waves are either linearly or circularly polarized. Both configurations have in common that there are one-dimensional trajectories on which the electron can oscillate with vanishing Lorentz force. The dynamics is analyzed for the situations when the electron moves in the vicinity of these ideal axes. If the laser intensities imply nonrelativistic electron dynamics, the system is described quantum mechanically. A semiclassical treatment renders the strongly relativistic regime accessible as well. To describe relativistic wave packets, the results of the classical analysis are employed for a Monte Carlo ensemble. This allows for a comparison of the wave packet dynamics for both configurations in the strongly relativistic regime. It is found for certain cases that relativity slows down the dynamics, i.e., for higher laser intensities, wave packet spreading and the drift away from the ideal axis of vanishing Lorentz force are shown to be increasingly suppressed

Analytical Approach to Wave Packet Dynamics of Laser-Driven Particles beyond the Dipole Approximation

An analytical approach to quantum mechanical wave packet dynamics of laser-driven particles is presented. The time-dependent Schroedinger equation is solved for an electron exposed to a linearly polarized plane wave of arbitrary shape. The calculation goes beyond the dipole approximation, such that magnetic field effects like wave packet shearing are included. Analytical expressions for the time-dependent widths of the wave packet and its orientation are established. These allow for a simple understanding of the wave packet dynamics

Relativistic effects in bound two-particle systems

The predictions of relativistic Schrödinger theory (RST) for the relativistic effects in helium-like ions with high nuclear charge ($Z\sim 30$-80) are elaborated in the electrostatic approximation (i.e. neglection of the magnetic interactions). The corresponding RST results are found to meet with the experimental data and with the predictions of other theoretical approaches, provided an estimate of the (neglected) magnetic effects is taken into account. This suggests to carry through high-precision calculations (including the magnetic forces) in order to further test the physical significance of RST