SHORT-PULSE TERAHERTZ RADIATION FROM HIGH-INTENSITY-LASER-PRODUCED PLASMAS

The interaction between high-intensity, ultrashort laser pulses and plasmas leads to the emission of coherent, short-pulse radiation at terahertz frequencies. In this work we discuss a model for this effect and its experimental realization. Our measurements constitute the direct observation of laser-induced. wake fields. From gas-density targets, resonant enhancement of the terahertz emission is observed if the plasma frequency is close to the inverse pulse length of the exciting laser pulse. :At higher plasma densities, the emission of subpicosecond, unipolar electromagnetic pulses is observed. With the use of solid density targets, emission of more than 0.5 mu J of far-infrared-radiation energy was measured. Simultaneous emission of MeV x rays and 0.6-MeV electrons was observed and correlated with the terahertz emission. This indicates that the radiative processes in such plasmas are driven by ponderomotively induced space-charge fields in excess of 10(8) V/cm.