Observation of Gigawatt-Class THz Pulses from a Compact Laser-Driven Particle Accelerator

We report the observation of sub-picosecond terahertz (T-ray) pulses with energies $geq460$ $mu$J from a laser-driven ion accelerator, thus rendering the peak-power of the source higher even than that of state-of-the-art synchrotrons. Experiments were performed with intense laser pulses (up to 5*10^19 W/cm²) to irradiate thin metal foil targets. Ion spectra measured simultaneously showed a square law dependence of the T-ray yield on particle number. Two-dimensional particle-in-cell simulations show the presence of transient currents at the target rear surface which could be responsible for the strong T-ray emission.