The interaction of a laser-produced electron beam with an ultraintense laser pulse in free space is studied. We show that the optical pulse with $a_0=0.5$ imparts momentum to the electron beam, causing it to deflect along the laser propagation direction. The observed 3-degree angular deflection is found to be independent of polarization and in good agreement with a theoretical model for the interaction of free electrons with a tightly focused Gaussian pulse, but only when longitudinal fields are taken into account. This technique is used to temporally characterize a subpicosecond laser-wakefield-driven electron bunch. Applications to electron-beam conditioning are also discussed.

• Received 18 October 2004

DOI:https://doi.org/10.1103/PhysRevLett.95.035004