Role of Coulomb focusing on the electron transverse momentum of Above-Threshold Ionization.

We have investigated the 2D photoelectron momentum spectra for ATI of atoms exposed to linearly polarized pulses by quantum mechanical calculations. By comparing the 2D momentum spectra for the long-range and short-range Coulomb potentials, the focusing of the electron transverse momentum by the long-range interaction is clearly revealed. Analysis indicates that the Coulomb attraction of the parent core to the returning electron is responsible for the focusing of the electron transverse momentum. Moreover, the strong dependence of the focusing of the electron transverse momentum on the laser wavelength and intensity is discussed.