Few-Cycle THz Emission from Cold Plasma Oscillations

We report on THz emission from plasma oscillations in semiconductors excited by femtosecond optical pulses. Time-resolved correlation measurements are performed on p-i-n and n -doped GaAs structures. In p-i-n structures coherent oscillations of the hot photogenerated carrier plasma 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 leading to an efficient emission of few-cycle THz radiation. {copyright} {ital 1997} {ital The American Physical Society}