Nonequilibrium theory of the optical Stark effect and spectral hole burning in semiconductors.

We consider the influence of intense coherent laser fields on the electronic and optical properties of semiconductors. Using nonequilibrium Green's function techniques and exploiting the analogies to superconducting and Bose condensed systems, we discuss the nature of the renormalizations and the collective excitations in the collisionless regime. Experimentally, this situation can be realized i) under nonresonant excitation of virtual electron-hole pairs and ii) under resonant excitation with ultrashort pulses. We explain the recently observed optical Stark effect as well as spectral hole burning and derive from first principles the longitudinal and transverse dielectric functions including exciton correlations.