[en] Laser pulses with a power of 10¹² W and a duration of 10^-13 s were focused onto both gas and solid targets. Strong emission of pulsed radiation at terahertz frequencies was observed from the resulting plasmas. The most intense radiation was detected from solid density targets and was correlated with the emission of MeV x rays and electrons. Results indicate that radiative processes in such plasmas are driven by ponderomotively induced space charge fields in excess of 10⁸ V/cm. This work constitutes the first direct observation of a laser-induced wake field