Resonantly enhanced multiphoton ionization of krypton and xenon with intense ultraviolet laser radiation

The absolute yield of singly and multiply charged ions of krypton and xenon and resulting photoelectron spectra produced by intense laser radiation in the range 285–310 nm are presented. Enhancement of the yield of ${\mathrm{Kr}}^{+}$ by two orders of magnitude in the vicinity of the 4$p^5$4d and 4$p^5$4d’ manifolds is observed at intensities exceeding ${10}^{13}$ W/${\mathrm{cm}}^2$. These observations extend the intensity at which strong resonant enhancement has been observed in multiphoton ionization by two orders of magnitude. A model incorporating line shifts and linewidths scaling linearly with intensity is in good agreement with the experimental results. Absolute cross sections for multiphoton ionization of xenon and krypton are presented and compared with recent theoretical calculations.