Optical Nonlinearity and Bistability due to the Biexciton Two-Photon Resonance in CuCI

Abstract

It is well established that biexcitons can be generated directly by two-photon absorption in CuCI. The intensity dependent nonlinearity arising from this resonance can be used to obtain optical bistability. Recently, Koch and Haug(1) and also Hanamura(2) have predicted the possibility of a bistable operation in a CuCI Fabry-Perot etalon. Hanamura uses a density matrix formalism and predicts that the switching can respond in a picosecond time scale due to the virtual formation of biexcitons. Koch and Haug obtain the complex dielectric function from a Green's function formalism and suggest a bistable behavior for a thin CuCI slab. They use a constant value for the biexciton linewidth, γxx, and a zero value for the exciton linewidth, γx. Their results indicate that a 1-μm-thick CuCI etalon, with natural reflecting surfaces, can give rise to bistability with a switch-on intensity of about 0.1 MW/cm2. The biexciton resonance, however, is located on the tail of the exciton resonance, which acts as a background absorption.