Effects of spatial dispersion and damping on exciton absorption

Exciton absorption is studied in the spatially dispersive case. The energy-propagation properties of the medium are used to define the absorption coefficient. The interplay of dispersion and damping in determining the absorption coefficient is discussed and a critical value of the damping above which the dispersion effects disappear is derived analytically. Furthermore, the dependence of the spectral and of the integrated absorption coefficient on the auxiliary boundary condition is discussed.