arXiv subjects

Gerd van de Sand

Publications and source records attributed to Gerd van de Sand.

4 recordsLinked to original sources

arXiv2000

Semiclassical description of multiphoton processes

We analyze strong field atomic dynamics semiclassically, based on a full time-dependent description with the Hermann-Kluk propagator. From the properties of the exact classical trajectories, in particular the accumulation of action in time, the prominent features of above threshold ionization (ATI) and higher harmonic generation (HHG) are proven to be interference phenomena. They are reproduced quantitatively in the semiclassical approximation. Moreover, the behavior of the action of the classical trajectories supports the so called strong field approximation which has been devised and postulated for strong field dynamics.

physics.atom-ph↗

arXiv2000

Inelastic semiclassical Coulomb scattering

We present a semiclassical S-matrix study of inelastic collinear electron-hydrogen scattering. A simple way to extract all necessary information from the deflection function alone without having to compute the stability matrix is described. This includes the determination of the relevant Maslov indices. Results of singlet and triplet cross sections for excitation and ionization are reported. The different levels of approximation -- classical, semiclassical, and uniform semiclassical -- are compared among each other and to the full quantum result.

physics.atom-ph↗

arXiv1999

Irregular orbits generate higher harmonics

The spectrum of higher harmonics in atoms calculated with a uniformized semiclassical propagator is presented and it is shown that higher harmonic generation is an interference phenomenon which can be described semiclassically. This can be concluded from the good agreement with the quantum spectrum. Moreover, the formation of a plateau in the spectrum is specifically due to the interference of irregular, time delayed, trajectories with regular orbits without a time-delay. This is proven by the absence of the plateau in an artificial semiclassical spectrum generated from a sample of trajectories from which the irregular trajectories (only a few percent) have been discarded.

physics.atom-ph↗

arXiv1998

Semiclassical time--dependent propagation in three dimensions: How accurate is it for a Coulomb potential?

A unified semiclassical time propagator is used to calculate the semiclassical time-correlation function in three cartesian dimensions for a particle moving in an attractive Coulomb potential. It is demonstrated that under these conditions the singularity of the potential does not cause any difficulties and the Coulomb interaction can be treated as any other non-singular potential. Moreover, by virtue of our three-dimensional calculation, we can explain the discrepancies between previous semiclassical and quantum results obtained for the one-dimensional radial Coulomb problem.

physics.atom-ph↗