Lawrence Berkeley National Laboratory

The temporal pro le of relativistic laser-plasma-accelerated electron bunches has been characterized. Coherent transition radiation at THz frequencies, emitted at the plasma-vacuum boundary, is measured through electro-optic sampling. The data indicates that THz radiation is emitted by a skewed bunch with a sub-50 fs rise time and a ~; 600 fs tail (half-width-at-half-maximum), consistent with ballistic debunching of 100 percent-energy-spread beams. The measurement demonstrates both shot-to-shot stability of the laser-plasma accelerator and femtosecond synchronization between bunch and probe beam.