Strong species dependence of high order photoelectron production in alkalimetal atoms

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