Polariton dynamics in quantum wells studied by femtosecond four-wave mixing

The dynamics of the polarization on the polariton branches can be studied directly by spectrally resolving the diffracted wave in femtosecond four-wave mixing. This is exemplified on semiconductor multiple quantum wells. The transition from excitonlike to polaritonlike behavior is accomplished experimentally by means of a strong perpendicular magnetic field that significantly influences the oscillator strength and hence the longitudinal-transverse splitting. Solutions of the Maxwell-Bloch equations are in qualitative agreement with the experiment.