Rescattering nonsequential ionization of Ne3+, Ne4+, Ne5+, Kr5+, Kr6+, Kr7+, and Kr8+in a strong, ultraviolet, ultrashort laser pulse

The ionization of Ne and Kr at 400 nm has been measured from 10${}^{13}$ to 10${}^{17}$ W/cm${}^{2}$ for charge states up to Kr${}^{8+}$. Nonsequential ionization is seen in the higher charge states Ne${}^{3+}$, Ne${}^{4+}$, Ne${}^{5+}$, Kr${}^{5+}$, Kr${}^{6+}$, Kr${}^{7+}$, and Kr${}^{8+}$ when the atomic response to the increasing external field strength moves from multiphoton to tunneling. A similar development in nonsequential ionization is seen in a semiclassical model and an empirical model of rescattering. The models show that nonsequential ionization not apparent in lower charge states can become prominent for higher charge states. It is possible to generalize these results and predict optimal wavelengths for multielectron excitation via nonsequential ionization. The findings indicate that ultraviolet to vacuum ultraviolet wavelengths can give the largest recollision for higher charge states.