PHOTOELECTRON INITIAL CONDITIONS FOR TUNNELING IONIZATION IN A LINEARLY POLARIZED LASER

A precise measurement of the initial kinetic energy of photoelectrons born in a high-intensity, Linearly polarized laser has been made in th e long-pulse tunneling limit. The shape of the angular distribution of electrons outside the laser focus is related to the initial momenta t he electrons gain from the field. The measurements of nonzero drift mo menta for high-charge states of neon indicate tunneling ionization is occurring and agree with the predictions of the Ammosov-Delone-Krainov (ADK) model [M. V. Ammosov, N. B. Delone, and V. P. Krainov, Sov. Phy s. JETP 64, 1191 (1986)]. The validity of this model allows the value of the electron's initial kinetic energy to be limited to approximatel y 0.2% of its average quiver energy. [S1050-2947(98)07008-5].