Coherent exciton interactions: Dependence on excitation fluence and polarization

The coherent interaction between excitons is revisited by examining the influence of coherent photo-excited excitons on the absorption spectra of ZnSe/ZnMgSSe multiple quantum wells for various polarization configurations. For purely resonant excitation at the heavy-hole exciton, a blueshift of the exciton absorption is found. This distinct blueshift shows a linear dependence on excitation fluence, but with different slopes for different polarization configurations. In the coherent regime the smallest shift is found for an orthogonal linear polarization of the pump and probe, noticeably smaller than the shift for same linear polarization. The strongest shift is found for the same circular polarization. Furthermore, we demonstrate experimentally that pump and probe and four-wave mixing spectra contain equivalent information about the shift and broadening of the exciton line. A linear correlation between the blueshift and the homogeneous linewidth is found in both pump and probe and four-wave mixing.