Observation of the modulation instability and frequency-doubling in self-defocusing crystal

► We observe modulation instability and frequency-doubling by the same setup. ► In experiment we use self-defocusing photorefractive crystal LiNbO3:Fe. ► Frequency-doubling means the increasing of interference fringes spatial frequency. ► Frequency-doubling appears when the nonlinearity of the c-axis is bigger.