Ionization rates for He, Ne, and Ar subjected to laser light with wavelengths between 248.6 and 390 nm

Using the R-matrix Floquet approach, we have investigated multiphoton single ionization of helium, neon, and argon subjected to laser light with a wavelength between 248.6 and 390 nm. For a wavelength of 390 nm, we have investigated ionization rates for Ne and Ar at intensities up to 2.5x10(14) W/cm(2). In this intensity regime, the ionization rates no longer follow the multiphoton I-N power law. At an intensity of 2x10(14) W/cm(2), a tunneling model approximates the Ar ionization rates within a factor 3, but the differences are much larger for Ne. The ionization rates at 390 nm are affected by intermediate resonances, with these resonances both enhancing and inhibiting ionization. Multiphoton ionization cross sections for Ne and Ar at 248.6 nm have also been determined.