Light Reflection from Inhomogeneous Dielectric Formed by High Density Z₃-Excitons in CuCl

抄録

Photo-induced reflectivity change in Z₃-exciton region of a CuCl single crystal ∼3.4 μm thick has been studied to monitor the inhomogeneous distribution of high density excitons. A pump and probe technique has been used. The results have been analyzed qualitatively using a model in which the reflection of light from a dielectric composed of a directly photo-modulated thin layer and a moderately modulated remaining region is treated. In a typical case of ∼5 MW/cm² excitation at 3.234 eV at 1.6K, the shift of the Z₃-exciton energy and its damping constant in the directly modulated layer have been estimated to be 3±1 meV and 4±1 meV, respectively. The effective thickness of the layer has been evaluated to be less than 0.2 μm. A fact suggesting the propagation of photo-excitation effects toward the rear surface region which is far apart compared with the penetration depth of the pump beam has been found.