EXCITON REDSHIFT FOR COHERENT PUMPING NEAR THE ABSORPTION-EDGE

The excitons are studied for a direct-gap semiconductor irradiated with a strong monochromatic laser beam near the exciton resonance. Starting from the Bethe-Salpeter equation in the screened-ladder approximation for the system polarization function, we study the pump-field influence on the excitons in the collision-free limit. Far from the absorption edge the results for the excitonic optical Stark effect are confirmed. For pump frequencies near the nominal Is-exciton position we propose a change from the blueshift to a redshift of the exciton. Physical reasons for this, and the experimental observability are discussed.