FIELD-IONIZATION OF NOBLE-GAS ATOMS WITH A KELDYSH ADIABATICITY PARAMETER OF THE ORDER OF ONE

Laser ionization of neutral atoms using linearly and circularly polari zed light is compared in xenon and neon gases. The laser used for thes e experiments is operated at 1053-nm wavelength and 1.9-ps pulse lengt h with intensities ranging from 10(13) to 10(15) W/cm2. The intensity required to ionize with circular polarization is approximately a facto r of 2 higher than that required with linear polarization. This is con sistent with nonresonant field-ionization models. The ionization of ne utral Xe occurs with the Keldysh adiabaticity parameter gamma approxim ately 1, showing that the field-ionization picture is valid for gamma less-than-or-equal-to 1 rather than the usually quoted gamma much-less -thn 1.