Influence of exciton-exciton interactions on frequency-mixing signals in a stable exciton-biexciton system

Transient nondegenerate four-wave mixing was performed in the femtosecond domain on a stable exciton-biexciton system. For excitation with two spectrally narrow pulses of frequencies omega (1) and omega (2) that have no spectral overlap with each other, only a frequency-mixing signal at 2 omega (1)-omega (2) was observed. The polarization dependence of the frequency-mixing signal intensity changed dramatically with increasing frequency difference between the incident pulses. Our results demonstrate that the frequency-mixing signal is strongly correlated with the exciton dynamics and the dramatic change of its polarization dependence is caused by the exciton-exciton interactions.