Dynamic Stark effect in interacting electron-hole systems: Light-enhanced excitons

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Abstract
A model semiconductor driven by a strong classical monochromatic laser beam is investigated. The resulting energy spectrum is found to be renormalized as a function of laser intensity and frequency. The stationary state is controlled by contact with a phonon heat bath. This state can be described as a pinned Bose-condensed state, the order parameter of which considerably increases with the light intensity (‘‘light-enhanced excitons’’). The optical response with respect to a second weak light beam consists of a spectrum with amplifying, transparent, and absorbing sections. The so-called Coulomb enhancement is considerably modified.