Giant excitonic optical nonlinearity in ZnSe grown by molecular beam epitaxy

In the low exciton density regime, we study the optical nonlinearity in the exciton resonant region in ZnSe grown by MBE on a GaAs substrate. At low temperature, excitons in bulk ZnSe largely contribute to enhance the nonlinearity. Using reflection type polarization spectroscopy with weak picosecond pulses, we evaluate third-order susceptibility and obtain huge value of χ⁽³⁾, over 10^-2 esu. From a degenerate four-wave mixing experiment with different polarization combinations, it is found that this huge nonlinearity originates from the exciton-exciton interaction.