Abstract
Multiphoton ionization rates have been calculated for He at the KrF laser wavelength of 248 nm and for laser intensities up to 6 × 1014 W cm-2 using the R -matrix Floquet method. For intensities above that at which channel closing takes place it is found that intermediate five-photon resonances with bound states strongly influence the total rate. In particular, the resonance between the ground state and the 1s2p 1 Po state is found to occur at a laser intensity of 5 × 1014 W cm-2 . This resonance is investigated at several neighbouring wavelengths and its prominent nature, which is discussed in terms of a proposed nearby laser-induced degenerate state, should enable it to be observed experimentally.

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