Univ Gottingen Inst Theoret Phys W-3400 Gottingen Germany
Max Planck Inst Festkorperforsch W-7000 Stuttgart Germany

A simple two-band model of a semiconductor in the presence of an arbitrarily strong pump laser is considered. Restricting the excitation strength to a finite part of the sample leads to a qualitative difference between resonant and nonresonant excitation of electron-hole pairs. For noninteracting electrons the dynamics can be solved exactly in the framework of scattering theory. Optically induced band gaps only show up in the local density of states in the excitation region. A sharp momentum selection rule for increasing excitation region only occurs for small excitation strength, while for larger excitation strength the weakening of the momentum selection rule is related to the width of the optically induced band gap in the infinite system.
 

PHYSICAL REVIEW B-CONDENSED MATTER, 44 7965-7974, 1991.