Coulomb-Volkov approximation for near-threshold ionization by short laser pulses

The formation of near-threshold structures in the angle-resolved photoelectron spectrum, the cusp in the transverse electron momentum distribution, and the forward-backward asymmetry is influenced by the residual Coulomb potential of the remaining atomic core acting on the electron detached by strong short-laser pulses. We show that an improvement beyond the strong-field approximation---the Coulomb-Volkov distorted wave approximation---is capable to reproduce these features found in the exact solution of the time-dependent Schr\"odinger equation in the multiphoton regime and the transition from the multiphoton to the tunneling regime.