Results of computer simulations concerning gain spectra of In0.05Ga0.95As quantum wells are
presented. A novel multi-plasmon concept of a light absorption and laser gain of low-
dimensional structures is comprehensively discussed. A generalized theory of multi-plasmon
optical transitions in direct gap quantum wells is developed using the cumulant expansion
method and fluctuation-dissipation theorem. Multi-quantum LO-phonon-plasmon optical
transitions are investigated with account on coherent memory effects in quantum wells. It is
shown that a red shift of the absorption edge can be caused not only by the well-known
mechanism of band gap shrinkage but also by multi-plasmon transitions. The comparison
with other theories and experimental data measured in In0.05Ga0.95As quantum wells is given.
