Absorption gratings in ferroelectric Bi4Ti3O12

Ti3O12. Basic properties of absorption gratings in this crystal are investigated with beam-coupling experiments. Depending on the grating spacing, wavelength, and intensity of the writing beams, an absorption grating in our sample can be either in phase or shifted by 180° with respect to the light pattern. The formation mechanism of absorption grating is discussed and proposed to originate from a shallow-trap effect.