Atoms and Electrons in Intense Laser Beams

We report the first direct observation of electron inelastic scattering from the ponderomotive potential of an intense pulse in vacuum. Electrons gained up to 0.2 eV when scattered from the temporal leading edge of a 1064 nm (1.165 eV) 140 picesecond laser pulse, and lost comparable amounts of energy when scattered from the trailing edge. When directed to the most intense part of the pulse, they were deflected out of the beam.