Interaction of two counterpropagating waves in a Ca:Ga:Bi12TiO20 crystal upon photoinduced absorption of light

It is shown that the interaction of counterpropagating coherent light beams at a wavelength of 633 nm in a Bi₁₂TiO₂₀:Ca:Ga crystal leads to the formation of a holographic reflection grating, which is a combination of phase and amplitude components related to photoinduced perturbations of the refractive index and absorption coefficient of the crystal. The formation of the grating is accompanied by a photoinduced decrease in the absorption coefficient of light Δα by -0.07 cm^-1. Photoinduced bleaching of the crystal occurs when the crystal is exposed to incoherent radiation at 600 nm (Δα= -0.12 cm^-1), while an increase in absorption is observed upon irradiation at 570 nm.