Ultra-intense laser-driven target normal sheath radiation in the terahertz region

Ultra-intense radiation in the terahertz (THz) regime emitted from the rear side of laser-irradiated solid target is experimentally investigated using a 20 TW fs laser system. The THz radiation emitted in a conical angle around 45 degrees is of radially polarized and has its duration of tens of ps. The waveform, angular distribution, polarization and laser intensity dependence of the observed radiation are in good agreement with those predicted for the radiation from deceleration of >sub-MeV electrons passing through the sheath electric field behind the target.