Analysis of reduced interband absorption mechanisms in semiconductor quantum wells

Mechanisms for reduced interband absorption using intersubband coherence or intersubband coupling in semiconductor quantum wells are analyzed by exactly solving the density matrix equation. By placing some mild limitations on the diagonal density matrix elements, general analytic solutions are obtained without weak-field restrictions. Our solutions demonstrate reduced absorption, various nonlinear processes, and coupling-field-modulation of interband transitions. Our results agree well with previous results for three-level atomic systems, give insights into nonlinear mechanisms, and point out the importance of nonperturbative approaches to this class of problems.>