Electro-optic and photorefractive two-beam coupling properties of lead barium niobate crystals

Lead barium niobate crystals (Pb_1-xBa_xNb ₂O₆) are attractive photorefractive materials for holographic data storage. The electro-optic coefficients r₃₃ and r₁₃ are determined using a Mach-Zehnder interferometer setup, and are measured to be 160±20 and 32±4 pm/V, respectively. The angular dependence of the photorefractive two-beam coupling gain is also investigated, and the products of the electro-optic coefficients and the electron-hole competition factor rζ are determined and compared with the electro-optic coefficients obtained using the interferometric method. It is found that the electron-hole competition factor is at least 0.7, indicating that the photorefractive process is mostly due to electrons. The effective trap densities at several wavelengths are also determined from the gain dispersion measurements, and are found to be 1.3-2.2×10¹⁶ cm^-3.