Strong species dependence of high order photoelectron production in alkali metal atoms

We present a theoretical and experimental study of the production of very high order photoelectrons from alkali metal atoms interacting with intense, midinfrared radiation. The strength of this process shows an unexpectedly strong species dependence. We find that this dependence can be explained via the difference in the cross section for electron-ion scattering from the different atoms. This allows us to directly relate the high energy portion of the photoelectron spectrum to specific features of the electron-ion potential.