Comparison between exact numerical solution and quantum orbit theory

D. Bauer, D.B. Milosevic, and W. Becker

As the laser pulse duration approaches the few-cycle regime, angle-resolved photoelectron
spectra become strongly dependent on the carrier-envelope phase. Pronounced interference
patterns in the rescattering plateau have been attributed to the interference of the
relevant electron trajectories that lead to the same final energy. This interpretation in
the spirit of Feynman's path integral approach yields an intuitive physical understanding
while the actual calculation requires several simplifying assumptions, in particular the
neglect of Coulomb effects once the electron is emitted, and a simplified view of the
rescattering process.

The numerical solution of the time-dependent Schroedinger equation (TDSE), on the other
hand, yields the exact final wave function and thus all observables of interest, often,
however, without revealing the dominant physical processes. A window-operator method is
proposed that allows to extract energy-resolved wave packet information from the exact
wave function, facilitating a sensitive test of quantum orbit theory. The case of atomic
hydrogen in linearly and circularly polarized few-cycle pulses is discussed. Photoelectron
spectra obtained from the numerical solution of the TDSE are compared with those predicted
by the strong field approximation.