Study of the self-defocusing in LiNbO sub(3):Fe,Mg crystals

We present an experimental study of the photorefractive self-defocusing in LiNbO sub(3):Fe,Mg crystals which is investigated by using the Z-scan technique. The self-defocusing effect nonlinearity appears weak in LiNbO sub(3):Fe,Mg crystals. The experimental results show that self-defocusing is due to the photorefractive lens-like effect. The holographic recording and two-wave mixing are investigated in order to explain this effect in LiNbO sub(3):Fe,Mg crystals. We describe the principle and application of Z-scan technique, and analyze the single wavelength Z-scan measurements of the nonlinear absorption coefficient and the nonlinear refractive index and its sign of the samples LiNbO sub(3):Fe and LiNbO sub(3):Fe,Mg.