Coherent radiation in the 0.3-3 THz range has been generated from femtosecond electron bunches at a plasma-vacuum boundary via transition radiation. The bunches produced by a laser-plasma accelerator contained 1.5 nC of charge. The THz energy per pulse within a limited 30 mrad collection angle was 3-5 nJ and scaled quadratically with bunch charge, consistent with coherent emission. Modeling indicates that this broadband source produces about 0.3 microJ per pulse within a 100 mrad angle, and that increasing the transverse plasma size and electron beam energy could provide more than 100 microJ/pulse.

Gamma-neutron activation experiments have been performed with relativistic electron beams produced by a laser wakefield accelerator. The electron beams were produced by tightly focusing ͑spot diameter Ϸ6 m) a high power ͑up to 10 TW͒, ultra-short (у50 fs) laser beam from a high repetition rate ͑10 Hz͒ Ti:sapphire ͑0.8 m͒ laser system, onto a high density (Ͼ10 19 cm Ϫ3) pulsed gasjet of length Ϸ1.5 mm. Nuclear activation measurements in lead and copper targets indicate the production of electrons with energy in excess of 25 MeV. This result was confirmed by electron distribution measurements using a bending magnet spectrometer. Measured ␥-ray and neutron yields are also found to be in reasonable agreement with simulations using a Monte Carlo transport code.

The temporal profile of relativistic laser-plasma-accelerated electron bunches has been characterized. Coherent transition radiation at THz frequencies, emitted at the plasma-vacuum boundary, was measured through electro-optic sampling. Frequencies up to the crystal detection limit of 4 THz were observed. Comparison between data and theory indicates that THz radiation from bunches with structure shorter than approximately = 50 fs (root-mean-square) is emitted. The measurement demonstrates both shot-to-shot stability of the laser-plasma accelerator and femtosecond synchronization between bunch and probe beam.