Spectral signatures of x((5)) processes in four-wave mixing of homogeneously broadened excitons

The influence of fifth-order coherences on the spectrally resolved four-wav e mixing response of predominantly homogeneously broadened quasi-two-dimens ional excitons is studied. Fifth-order signatures are discussed as a functi on of spectral position and excitation polarization. An exciton-biexciton b eating for positive delay times is the dominant effect, which is pronounced at the exciton-biexciton transition for collinearly polarized excitation a nd at the exciton transition for cross-linearly polarized excitation. For n egative delay times and collinearly polarized excitation a pronounced excit on-biexciton beating at the exciton resonance is observed that is vanishing for long negative delays owing to the faster dephasing in the two-exciton continuum compared with the bound biexciton state. These results are in qua litative agreement with microscopic model calculations that include the coh erent dynamics of one- and two-exciton resonances up to the fifth order in the optical field. (C) 2001 Optical Society of America.