ABSORPTION GRATINGS IN FERROELECTRIC BI4TI3O12

Light-induced absorption changes are measured in ferroelectric Bi4Ti3O 12. Basic properties of absorption gratings in this crystal are invest igated with beam-coupling experiments. Depending on the grating spacin g, wavelength, and intensity of the writing beams, an absorption grati ng in our sample can be either in phase or shifted by 180 degrees with respect to the light pattern. The formation mechanism of absorption g rating is discussed and proposed to originate from a shallow-trap effe ct.