Observation of Terahertz Emission from a Laser-Plasma Accelerated Electron Bunch Crossing a Plasma-Vacuum Boundary

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 $0.3\mu \mathrm{J}$ per pulse within a 100 mrad angle, and that increasing the transverse plasma size and electron beam energy could provide more than $100\mu \mathrm{J}/\mathrm{p}\mathrm{u}\mathrm{l}\mathrm{s}\mathrm{e}$.