Nonlinear phase-resolved polariton spectroscopy in ZnSe epilayers

The influence of thermalized carriers on the exciton polariton propagation in a semiconductor ZnSe layer is investigated by reflection spectroscopy. Reflected laser pulses are characterized in amplitude and phase by using the method of spectral interferometry (SI). The complex coefficient of reflection is given for the low excitation density by a broadened Elliot formula. For increasing density scattering between the carriers and the laser-induced polarization is accounted by the solution of the semiconductor Bloch equations. In the spectral phase we find a delicate dependence of a π-jump at the heavy-hole resonance of the carrier density while the spectral amplitude practically remains the same.