Atomic Inner-Shell Excitation Induced by Coherent Motion of Outer-Shell Electrons

Outer-shell electrons coherently driven by intense radiation can transfer energy in a direct intraatomic process to inner-shell excitations. Provided that the effective momentum transfer $\Delta q$ is sufficiently low ($\Delta q\lesssim \frac{\hslash }{a_0}$), the amplitudes governing the coupling of the outer electrons to the atomic core constructively sum. The effective cross section, which can be related to fast atom-atom collisions (≳10 MeV/u), is evaluated in a limiting form closely resembling the Bethe result for inelastic electron scattering from atoms.