Abstract

According to the band-conduction model the erasure rate Γ of a photorefractive grating is given by where e is the electric charge, μm is the carrier mobility, and ε the dielectric constant along the direction of charge migration, n₀ is the density of free carriers, and f(k_g, ε) is a function that is nearly unity for small grating wavevector k_g. Because both the dielectric constant and the free-carrier mobility vary with direction in a BaTiO₃ crystal, the erasure rate Γ∝μ/ε of a photorefractive grating is also expected to depend strongly on the grating’s orientation. In fact, we find that it does not. Previous work¹ showed that pm/e is approximately independent of direction at T = 25 °C. To study μm/ε with ε changing, we heated a type A crystal² of BaTiO₃ from T = 16°C to 45°C. Over this range ε_⊥ decreases by 40%, while ε_|| increases by 20%. We find that the rates are the same for both grating orientations in spite of the different temperature dependencies of ε_⊥ and ε_||.

© 1991 Optical Society of America