Factors that influence the modulation instability in self-defocusing photorefractive crystal

We report on the experimental observation of the modulation instability in self-defocusing photorefractive LiNbO3: Fe crystal. Experimental results show that the modulation instability is related to the illumination time; and it is also related to the angle that between the direction of c-axis and the direction of the threadlike beam that illuminate the crystal. And the modulation instability is also related to the shape of the incident light.