Three-layer speckle structure in the photorefractive single crystal of lithium niobate

Integrated research of structural and optical homogeneities of the lithium niobate crystal with low photorefractive effect

“…This generates a complex pattern of maxima and minima of intensity (speckle pattern) the form of which is determined by the crystal structure and the features of its defect structure [1,2]. For the investigated crystals significantly changing over time three-layer structure of the PILS speckle pattern was observed [17], Fig. 1b.…”

“…Based on the geometry of the experiment (the distance from the crystal to the screen -b, distance between two brink points of the speckle pattern -a), scattering angle  was calculated by the formula  = arctg(a/b). Since the shape of the indicatrix of the scattered radiation can be varied and multiple [1,17] the outermost point of the PILS picture at which the scattering angle is determined was taken. It is the point at which the intensity of scattered radiation decreases tenfold.…”

Microstructures in ferroelectric lithium niobate single crystals

“…3). The step-wise appearance and development (fluctuating micro-structures-static microstructures-continuous trail) of the laser track revealed in single crystals by the study correlate with the development of triple-layer speckled patterns at photo-refractive light scattering (undesirable at recording) in a lithium niobate single crystal [3]. We have observed the periodic structure of a laser beam directed along the polar axis (Z) of a stoichiometric lithium niobate single crystal grown from melt of 58.6 mole % Li 2 O (Fig.…”

“…Recent studies have shown the structural heterogeneities of nano-, micro-and macro-scales emerging inevitably during non-equilibrium crystallisation along with clusters containing localised electrons formed by intrinsic and admixed defects, fractal structures, and laser-induced defects, all being responsible for optical properties of ferroelectric photo-refractive single crystals [1][2][3][4][5][6]. The studies on the processes creating the structures that affect photo-refraction and other properties of materials are scarce.…”

Complex study of the structural and optical homogeneity of lithium niobate crystals

“…In patterns obtained by laser conoscopy, in contrast to the cono scopic patterns observed in a polarization microscope, the large image size makes it possible to perform a detailed analysis of distortions in crystals both in the center of the field of view and at the periphery. This possibility is urgent for detecting and studying the fine features of structural and growth distortions, micro and nanostructures (which inevitably exist, especially in doped single crystals, due to the inhomogeneous dopant incorporation into the structure), and laser induced distortions in photorefractive single crystals [14][15][16].…”