Improvements of sensitivity and refractive-index changes in photorefractive iron-doped lithium niobate crystals by application of extremely large external electric fields

Applying external electric fields of as much as 65 kV/mm reveals significant enhancement of refractive-index changes Δns and of photorefractive sensitivity S. Samples with different iron concentrations and oxidation–reduction states were investigated. Refractive-index changes of up to Δns=11.5×10-4 and sensitivities as high as S=40 cm/J were measured (ordinary light polarization; light wavelength, λ=488 nm). The refractive-index changes are space-charge limited, but the photorefractive sensitivity S exhibits for large externally applied electric fields a linear increase up to the highest field values used. No nonlinear enhancement of the charge transport was observed. However, the excellent high-field material performance and the record values for Δns and S obtained improve the applicability of LiNbO3 crystals.