Laser excitation and Beutler-Fano resonances

The experiment just described is one of a much more general class of studies in which the spectral properties of atoms are modified by a strong field laser and then probed by another laser - often chosen to have a weak field, so that it does not affect the atom further, although that is by no means essential. 

Even if only one laser is involved in probing existing spectral structure, the possibility must always be borne in mind that the strength of the laser field can modify the couplings within the atom, so that the autoionising line may exhibit a different profile from the one of the free atom in the weak field limit. This problem is actually quite involved, because bound 

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