Abstract

Ultrafast technology has created new opportunities for investigating the properties of many-body systems. For example, an intense pump optical pulse tuned in the transparency regime induces virtual charge fluctuations between the conduction and valence bands that renormalize all the semiconductor parameters. Augmented by correlation effects, such processes result in a "dressed" interacting system whose excitation spectrum can be measured by a weak probe pulse. The exciton absorption in undoped semiconductors was investigated with this technique in [1]. As the pump intensity increases, the bound state resonance shifts to the blue; this is called the AC (optical) Stark effect. Unlike atomic systems, in semiconductors the optically excited electrons and holes interact with each other; and many-body effects need to be addressed [2]. A narrow-band pump pulse blue-shifts the resonance and slightly enhances its oscillator strength [3,4]. The oscillator strength is significantly reduced if the pulse is ultrashort (100 fs or less) [5].

© 1994 Optical Society of America