Polaritonic effects in superlattices

We present a method to compute the optical functions of superlattices in the excitonic energy region including the effect of the coherence between the electron-hole pair and the electromagnetic field. The electron-hole screened Coulomb potential is adopted and the valence-band structure is taken into account in the cylindrical approximation, thus separating light- and heavy-hole motions. The: calculated optical functions have poles in correspondence to the polariton eigenvalues for a multiplicity of excitonic states. We also calculate the amplitudes of higher polariton branches and the line shapes of the optical functions. Numerical examples appropriate to GaAs/Ga1-xAlxAs superlattices are given and the effect of coherence is displayed in the line shape of the excitation spectrum.