Bloch Oscillations and Ultrafast Coherent Optical Phenomena

Abstract

In this chapter, we discuss Bloch oscillations and other ultrafast coherent optical phenomena. We address in particular the observation of such phenomena in semiconductor heterostructures, which are an ideal playground to observe these effects, since the potential landscape of such heterostructures can be nearly freely designed. Thus, they can be used to model many basic solid-state effects, which are related to coherent transport in solids, such as Bloch oscillations, Zener breakdown, and others. After introducing the time-resolved techniques to trace the wave-packet dynamics, we first discuss double wells, which are the simplest system to investigate coherent wave-packet motions in the solid state. We then generalize to multiwell systems, which directly leads to Bloch oscillations in biased semiconductor superlattices. The coherent oscillation generates terahertz (THz) radiation, thus opening the way for a novel class of tunable emitter devices. At very high electric fields, Zener tunneling can become a competing process: the coupling to higher bands leads to a directed transport along the field, preventing the Bloch oscillations. Finally, we discuss wave-function tomography experiments, where we directly probe wave functions using a novel experimental technique.