Multiphoton processes without the dipole approximation

Farhad H. M. Faisal

Peter W. Milonni

An approach to the calculation of cross sections for laser-assisted excitation transfer processes is outlined for the dipole–dipole case. The internal atomic variables are treated in the Heisenberg picture, while the simplest form of semiclassical collision theory is used for the atomic trajectories. A simple physical picture in the spirit of the Weizsäcker–Williams method emerges: The laser-assisted excitation transfer may be treated approximately as a single-atom multiphoton process in an applied field.

Farhad H. M. Faisal, A. Dalgarno

Avia Rosenhouse, Jacob Katriel

The multiphoton single-atom Dicke Hamiltonian in the dipole and the rotating-wave approximations is shown to reduce to the one-photon single-atom Dicke Hamiltonian via an approximate linearization process. For the special case of the Jaynes-Cummings Hamiltonian, it is shown that it is possible to derive a linearized form that is exactly equal to the original Hamiltonian.

Y. B. Band, Raanan Bavli, Donald F. Heller

P. Lambropoulos, Gary D. Doolen, Steven P. Rountree

It is shown that even for optical frequencies the dipole approximation is not always valid in multiphoton ionization. For certain photon frequencies, we find quadrupole-dipole contributions which are several orders of magnitude larger than the usual dipole-dipole contribution to two-photon ionization.