Giant Optical Nonlinearity of Exciton and Biexciton system in Semiconductors

Abstract

Abstract Optical nonlinearities at the exciton resonance in semiconductors are studied under weak excitation regime. Third order optical nonlinearity is clearly observed even in the case of resonant excitation in the wide range of the pumping power. In ZnSe, sharp resonance of the third order nonlinearity at the transverse exciton energy is observed. The saturation power of such resonant optical nonlinearity depends strongly on the pulse duration. In the case of short pulse excitation less than 5ps, the third order power dependence holds up to 100kW/cm 2 . In this power region we can evaluate the effective χ (3) and obtain very large value, such as to 6×10 −2 esu. Analyzing the polarization dependences of the degenerate four wave mixing signal, the contribution of the free or bound two-exciton state, namely biexciton state, is examined.