Light scattering in single crystals of nonlinear-optical photorefractive LiNbO3:Cu and LiNbO3:Zn

Abstract

535.36:548Comparative studies are made of the photorefractive scattering of light in nonlinear single crystals of lithium niobate with congruent compositions (LiNbO 3 ) doped with "photorefractive" Cu [0.015 mass %] and "nonphotorefractive" Zn [0.5 mass %] cations. For the first time it is found that single crystals doped with "photorefractive" and "nonphotorefractive" cations have different indicatrices for photorefractive light scattering. The aperture angle for photorefractive scattering reaches its steady state value more rapidly with high laser powers than with low. However, at high powers laser induced heating of the crystal is greater, and this leads to a narrowing of the scattering indicatrix. It is also found that photorefractive scattering in these single crystals depends on the region of the boule from which a sample has been cut. This indicates that there is a nonuniform distribution over the boule of the imperfections with localized electrons which determine the magnitude of the photorefractive effect.Introduction. Photorefractive recording of phase lattices, which is used for long-term memory and the creation of high selectivity devices for holographic recording, is currently far from perfection and is in a developmental stage [1,2]. To a significant extent this is because of a lack of optimal photorefractive single crystal materials [2]. One of the most promising materials for holographic information recording is single crystal lithium niobate (LiNbO 3 ), whose photorefractive properties can be varied over a wide range by varying the stoichiometry (the ratio R = Li/Nb) and doping [2][3][4][5]. Single crystals with a high photorefractive efficiency can be obtained by doping the lithium niobate structure with transition metal cations (Fe, Cu, Mn, Ni, etc.; "photorefractive" cations

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

“…The most anomalous behavior is typical for the LiNbO 3 :Cu (0.015 wt.%) bandwidth region, which indicates its high optical inhomogeneities apparently because of uneven distribution of defects as well as copper cations in the volume of the crystal. Heterogeneity of LiNbO 3 :Cu(0.015 wt.%) crystal is confidently shown on PILS pictures [2,7,9,11]. Edge position of the optical transmission of the third group crystals (LiNbO 3 :Y(0.46 wt.%) and LiNbO 3 :Y(0.24 wt.%):Mg(0.63)) is in good agreement with the first group crystals but the slope of the transmission curve to the xaxis is substantially less.…”

“…In literature mainly temporal changes of the second and third layers of PILS pattern been studied (described above) with different excitation radiation capacities [2,[7][8][9][10][11][12]. Temporal changes in the central (first) layer, directly in the passage of the laser beam, are studied least [1,23].…”

“…Raman spectra and PILS pictures of lithium niobate crystals of stoichiometric composition, as well as congruent crystals doped with cations listed above were investigated earlier in Refs. [2,4,[7][8][9][10][11][12][13][14]. Optical quality control and structural homogeneity of the grown crystals were carried out by laser conoscopy and electron spectroscopy.…”

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

“…In addition, these crystals are generally characterized by the nonuniform volume distribution of intrinsic and impurity defects [2,6,7]. Promising photorefractive materials are ferroelectric lithium nio bate crystals of stoichiometric composition (LiNbO 3st , R = Li/Nb = 1), as well as crystals of congruent com position (LiNbO 3con , R = Li/Nb = 0.946) doped with copper (LiNbO 3 :Cu) [2,[4][5][6][7][8][9][10]. Copper cations are multiply charged and may undergo charge exchange under illumination (Cu 2+ Cu + ) [9].…”

“…Promising photorefractive materials are ferroelectric lithium nio bate crystals of stoichiometric composition (LiNbO 3st , R = Li/Nb = 1), as well as crystals of congruent com position (LiNbO 3con , R = Li/Nb = 0.946) doped with copper (LiNbO 3 :Cu) [2,[4][5][6][7][8][9][10]. Copper cations are multiply charged and may undergo charge exchange under illumination (Cu 2+ Cu + ) [9]. However, the photorefractive properties of LiNbO 3 :Cu single crys tals practically have not been studied.…”