FEW-CYCLE THZ EMISSION FROM COLD-PLASMA OSCILLATIONS

We report on THz emission from plasma oscillations in semiconductors e xcited by femtosecond optical pulses. Time-resolved correlation measur ements are performed on p-i-n and n-doped GaAs structures. In p-i-n st ructures coherent oscillations of the hot photogenerated carrier plasm a emit THz radiation. A fundamentally new emission process is proposed in n-doped GaAs structures. Here, the screening of the surface field starts plasma oscillations of the cold electrons in the GaAs bulk lead ing to an efficient emission of few-cycle THz radiation.