Vector two-wavelength interaction on reflection holographic gratings in cubic gyrotropic photorefractive crystals

The interaction of two counterpropagating light waves on reflection holographic gratings is studied in cubic photorefractive crystals with the natural optical activity. The anisotropy of contributions from intramode (without a change in the refractive index of natural circularly polarised waves) and intermode processes to the interaction of the waves in a bismuth titanate crystal is considered. It is shown that the polarisation dependences of the effective gain and the polarisation vectors of the interacting light beams measured at a wavelength of 633 nm in a (100) cut Bi₁₂TiO₂₀:Fe, Cu crystal of thickness 2.6 mm well agree with numerical calculations with the use of the two-beam coupling constant equal to 6.8 cm^-1.