Resonances in atomic and molecular multiphoton processes

This essay discusses resonances that occur when multi-electron atoms and mo lecules are exposed to intense laser fields. The subject owes much to the f undamental studies by Ugo Fano on the interference of autoionizing states w ith continua giving rise to asymmetric peaks in excitation spectra. The app roach adopted is based on R-matrix Floquet theory, a nonperturbative ah ini tio method, which has been used to describe in a unified way a wide range o f multiphoton processes. The theory is illustrated by presenting results ob tained for resonances in the multiphoton spectra of He, Ar, and H-2. Finall y, the essay concludes by considering possible future directions of researc h.