Homogeneity of the photorefractive effect in reduced and unreduced KNbO3 crystals

It is obvious that the homogeneity of the photorefractive sensitivity has strong influence on devices such as optically driven spatial light modulators (SLM) 1-3. These applications involve two-dimensional image information and need position-independent transfer functions. The photorefractive homogeneity is based on the distribution of the photorefractive donor centers and traps in the crystal. Therefore it is affected by the crystal growth conditions and subsequent crystal treatments such as poling and electro-chemical reduction 4, 5.