Multi-mode description of an interacting Bose-Einstein condensate

Opt. Express 8, 92 (2001)

Krzysztof Goral, Mariusz Gajda, and Kazimierz Rzazewski

We study the equilibrium dynamics of a weakly interacting Bose-Einstein condensate trapped in a box. In our approach we use a semiclassical approximation similar to the description of a multi-mode laser. In dynamical equations derived from a full N-body quantum Hamiltonian we substitute all creation (and annihilation) operators (of a particle in a given box state) by appropriate c-number amplitudes. The set of nonlinear equations obtained in this way is solved numerically. We show that on the time scale of a few miliseconds the system exhibits relaxation -- reaches an equilibrium with populations of different eigenstates fluctuating around their mean values.

Ionization of hydrogen atoms by intense vacuum ultraviolet radiation

J. Phys. B 34, 2245 (2001)

Jaroslaw Bauer, Lukasz Plucinski, Bernard Piraux, Robert Potvliege, Mariusz Gajda and Jacek Krzywinski

We study the ionization of hydrogen atoms by an intense pulsed beam of photons with energies of 17 or 50 eV. The work is motivated by the demonstration of the free-electron laser (FEL) action at the DESY Laboratory. The parameters chosen for the incident field are in the regime accessible by the FEL. Ionization yields are obtained within three different approaches, namely the strong-field approximation, the Floquet method and a numerical solution of the time-dependent Schrödinger equation. A marked stabilization effect for 50 eV photons is shown.