We calculate the photo-ionization cross-section from the ground state of thehelium atom, using the complex rotation method and diagonalization of sparsematrices. This produces directly the positions and widths of the doubly excited1Po resonances together with the photo-ionization cross-section. Ourcalculations up to the N=9 threshold are in perfect agreement with recentexperimental data and show the transition from a regular structure at lowenergy to a chaotic one at high energy, where various resonances stronglyoverlap.
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