Optimization of the photorefractive properties of KNbO3crystals

Photorefractive effects of pure and iron doped KNbO3 crystals with concentrations between 150 ppm and 300 ppm have been investigated. In order to optimize the photorefractive recording times and the amplitude of the refractive index changes the crystals were thermally treated with simultaneous photorefractive testing. The photoconductivity data and the photorefractive beam coupling gain dependent on the grating spacing show that the relative influence of electron and hole contribution is altered depending on the reduction treatment. The experimental results are discussed in terms of a two carrier model.