Picosecond beats in coherent optical spectra of semiconductor heterostructures: photonic Bloch and exciton-polariton oscillations

Propagation of short pulses of light in multilayer semiconductor structures containing excitons is modelled by solving time-dependent Maxwell equation s with the use of the scattering state technique. This approach allows this problem to be reduced to finding the eigenstates (scattering states) of th e system, subject to the stationary Maxwell equations with appropriate boun dary conditions. Then, the time-dependent electric field in the system can be found by Fourier integration of the scattering states. Application of th is technique to the problem of light-propagation in laterally confined Brag g mirrors reveals the effect of photonic Bloch oscillations, i.e., oscillat ions of photons between two inclined mini-gaps of the optical superlattice, analogous to the well-known electronic Bloch oscillations. The scattering state technique is applied to the problem of propagation of exciton-polarit ons in semiconductor films. The pulsed excitation induces a grating of diel ectric polarization in the direction of propagation of light, which arises through interference between two exciton-polariton branches. The grating ev olves backwards relative to the light propagation direction because of the multiple re-emission and re-absorption of photons by excitons. Inhomogeneou s broadening of excitons exerts a dramatic influence on the time-resolved c oherent optical spectra of semiconductor structures through the vertical mo tional narrowing effect in bulk crystals and multiple quantum wells (MQWs). The polariton interference governs the resonant Rayleigh scattering (RRS) spectra of the MQWs. In particular, a drastic difference between the RRS sp ectra of Bragg-arranged and anti-Bragg-arranged MQWs is predicted.