Ponderomotive effects on angular distributions of photoelectrons,.

We report the observation of intensity dependent angular distributions of photoelectrons in multiphoton ionization (MPI) of xenon by 1064nm light in the intensity range of .5 - 5x10(13) W/cm (2). The intensity dependence is shown to arise from the scattering of the photoelectrons from the ponderomotive potential created by the intense optical fields. This phenomena is a general, final-state effect which can severely restrict the usefulness of angular distribution measurements in high intensity MPI.