Optical Modulation near Intrinsic Absorption Edge in CdS Caused by Acoustic Domain Propagation

Abstract

Transmission modulation of the monochromatic light caused by propagation of an acoustic domain was first observed in CdS near intrinsic absorption edge. The modulation appears in an additional absorption and, as a consequence, in a shift of the absorption edge toward longer wavelength. The spectral dependence and the absorption dichroism of the effect are quite analogous to the field-induced absorption and can be explained qualitatively by Franz's theoretical formula. The transient change of the absorption during domain buildup is similar to the change of voltage drop across the domain rather than the acoustic flux itself. Quantitative studies also suggest the responsibility of the macroscopic d.c. field across the domain. Thus, the observed effect can be ascribed to the field-induced absorption due to the domain peak field of about 10 5 V/cm.