Coherent control of terahertz emission and carrier populations in semiconductor heterostructures

A short laser pulse exciting semiconductor heterostructures will induce a time-varying polarization that in turn leads to the generation of terahertz radiation. Although there are several possible mechanisms for this time-dependent polarization, some depend critically on the dephasing time of the photoexcited carriers. For long dephasing times it is possible to control both the populations and the coherence of these particles by proper shaping of the optical pulse. We discuss our recent experimental and theoretical work on coherent terahertz radiation emitted from semiconductor heterostructures when the exciting optical fields are shaped in both amplitude and phase. Our shaping techniques include phase-locked pulse generation in a Michelson interferometer and pulse-train generation by phase-only filtering.