Ionization rates for He, Ne, and Ar subjected to laser light with wavelengths between 248.6 and390nm

Abstract

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 $390\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. For a wavelength of $390\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, we have investigated ionization rates for Ne and Ar at intensities up to $2.5\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$. In this intensity regime, the ionization rates no longer follow the multiphoton ${I}^{N}$ power law. At an intensity of $2\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, a tunneling model approximates the Ar ionization rates within a factor 3, but the differences are much larger for Ne. The ionization rates at $390\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ are affected by intermediate resonances, with these resonances both enhancing and inhibiting ionization. Multiphoton ionization cross sections for Ne and Ar at $248.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ have also been determined.