RESONANCES IN THE MULTIPHOTON IONIZATION OF HELIUM AT 248nm

D.H. Glass and P.G. Burke

Department of Applied Mathematics and Theoretical Physics,
The Queen's University of Belfast, Belfast, BT7 1NN, UK

The R-matrix-Floquet approach has been used to obtain multiphoton
ionization rates in He for the KrF laser wavelength of 248nm.
Calculations have been carried out for intensities from below
10$^{13}$Wcm$^{-2}$ to about 5 $\times$ 10$^{14}$Wcm$^{-2}$.
A discussion is given of the role of channel closing and intermediate
resonances in the ionization process.