The method of spectral interferometry is applied to study the reflexion of laser pulses at semiconductor microstructures in the regime of linear response. Inside the semiconductor the light field is split into different excitonic polariton waves. Due to interference between them pronounced changes of phase and amplitude of light appear.

The investigations are directed on the influence of pumped carriers on the interference properties. In particular, the phase behaviour is sensitive to many-body effects between excited carriers, which influence the polariton properties. Starting at the non-excited semiconductor with increasing excitation the exciton features are washed out (Mott transition of excitons) and correspondingly the polariton interferences vanish.

Using semiconductor heterostructures with different electron-LO-phonon coupling strength the interplay of quantum kinetics of Coulomb scattering with the electron-LO-phonon scattering is investigated. Changing the time delay between pump and probe pulse new inside is expected on the dynamics of the excitation of semiconductors with short laser pulses and from more fundamental point of view on the coupling of light with the semiconductor.