February 7 , 2007

“Terahertz-optical spectroscopy of semiconductors: from “atomic” physics to terahertz optoelectronics”

Samuel Carter

JILA, Univ. of Colorado, Boulder

The optical properties of semiconductors are strongly influenced by excitons – bound electron hole pairs that behave as artificial atoms. I will discuss experiments in which transitions between exciton states in quantum wells are excited by intense terahertz radiation and probed by a weak near-infrared (NIR) beam. One of the most dramatic results is analogous to Autler-Townes splitting, an effect more commonly observed in atomic systems. The terahertz electric field strongly couples two exciton states, leading to a splitting in the NIR absorption. Mixing of the terahertz and NIR radiation also results in terahertz-optical sidebands, which provide a powerful spectroscopic tool. These results are an important step in understanding strongly driven quantum systems, and they also have important technological applications. The terahertz-driven quantum wells discussed here may represent the future of an existing optoelectronic device, the quantum well modulator. The presence of quantum coherence when these devices are driven at terahertz frequencies may lead to novel functionalities.