Rigorous coupled-wave diffraction theory is used to analyze two-wave and multiwave mixing in diffusion-controlled photorefractive barium titanate, which is modeled by the Kukhtarev equations. These equations are partially decoupled to yield a system of two equations between the electron density and the electrostatic field (and hence the induced refractive index profile). The transmitted and reflected optical fields, the dielectric modulation, the electrostatic field, and the electron density are studied for the cases in which the interfering, incident optical fields have equal and unequal amplitudes for different values of the linear refractive index mismatch and for different values of photorefractive crystal length. In each case the exact longitudinal inhomogeneity in the photorefractive medium is analyzed with the use of rigorous coupled-wave diffraction theory and an exact Kukhtarev analysis. We compare the evolution of the diffracted orders for different sample lengths to show that the nature of the steady state (oscillatory or nonoscillatory) critically depends on the sample length. Our computations study in BaTiO3 the conditions for temporal instability resulting in self-pulsation and for anisotropic diffraction contributing to significant generation of higher orders (assuming that two plane waves are incident on the photorefractive material).