The Continuum Approximation

A Jiménez, Luca Argenti, Fernando Martı́n

We present a study of radiative continuum-continuum transitions in helium in the presence of doubly-excited states by using the attosecond RABITT technique beyond the Single Active Electron approximation. On the one hand, transition amplitudes between correlated continuum states are calculated both by direct numerical solution of the time-dependent Schrodinger equation as well as with a two-photon perturbative model. The effect of autoionizing states on the sideband phaseshift is thus analyzed. On the other hand, we apply the soft-photon approximation to quantify the effects the IR probe intensity on the sideband non-resonant overtone components.

K. T. Hecht

Robin Shakeshaft, R. M. Potvliege

We formulate a nonperturbative approximation for treating the multiphoton ionization of an atom. Our approximate ionization amplitude is the time average of the matrix element for the electron, having absorbed enough photons to reach the continuum threshold, to jump into the continuum state represented by the Kroll-Watson scattering wave function.

Jean-Louis Basdevant

Bruce Cameron Reed

Erkki Kyrola

Studies the coupling of N discrete levels to a common continuum. The discrete levels, which can include both genuine bound states and autoionisation states, are assumed to be coupled to the continuum and to each other in such a way as to permit a rotating wave approximation in the Schrodinger equation. A general solution for the model is derived with the aid of Laplace transforms and the Weisskopf-Wigner approximation. The author discusses general properties of the discrete level populations and the electron spectrum like population trapping, zeros, crossings, resonances and confluences. As examples the author treats cases where two or three discrete levels interact with a continuum.