Laser beam break-up to regular optical patterns and refractive structures formation in a photo refractive lithium niobate crystal

Break-up of a cw 632.8 nm wavelength laser beam to regular optical patterns during propagation through a photo refractive iron doped lithium niobate (LN:Fe) crystal is demonstrated. The power of the laser beam is varied in the range of 0.02–10 mW and 4mm and 10 mm lengths LN:Fe crystals are used in the experiments. Time evolution of the laser beam profile at the output face of the LN:Fe crystal showed the splitting of a Gaussian beam into two lobes and then formation of 2D micrometric scale regular optical patterns. The input beam power increase essentially speeds-up the regular optical pattern formation. 2-fold rotation symmetry regular optical patterns induct the quasi-crystalline photonic structures in LN:Fe crystal. A physical model to explain the experimental results is discussed