Photorefractive Effects in LiNbO3 and LiTaO3

Abstract

Lithium niobate (LiNbO 3 ) and lithium tantalate (LiTaO 3 ) crystals have gained increasing interest during recent years because of their fascinating physical properties, such as piezoelectricity, ferroelectricity, pyroelectricity, birefringence, electrooptical, and nonlinear-optic effects. These properties have been successfully utilized for applications in various fields. Basic experiments on acoustic surface wave propagation, electrooptical modulation, optical wave guiding, second harmonic generation, and pyroelectric detection have been performed with these crystals.LiNbO 3 and its isomorphous compound LiTaO 3 are not found in nature. The first successful growth of large single crystals by the Czochralski technique was reported by Ballman [1]. A peculiarity results from the fact that the congruently melting composition (about 48.4 mol % Li 2 O) does not coincide with the stoichiometric one (50 mol % Li 2 O). The crystals have a perovskite-like structure with oxygen octahedra and are trigonal with only one structural phase transition (paraelectric-ferroelectric) at the Curie temperature T c of about 1150 • C for LiNbO 3 and about 610 • C for LiTaO 3 . The nonpolar high-temperature phase belongs to the space group R3c (point group 3m) and at T c the transition to the ferroelectric low-temperature phase of the space group R3c (point group 3m) occurs. At room temperature LiNbO 3 is negatively birefringent. The birefringence of LiTaO 3 is very small at room temperature and positive for the congruently melting composition. More information about growth and fundamental properties of LiNbO 3 can be found in [2,3]. 83

Optical nonlinearities of small polarons in lithium niobate

“…22 This bulk photovoltaic effect [23][24][25][26][27] is one of the most important features of doped LiNbO 3 , i.e., crystals with extrinsic defect centers, such as Fe Li . It is because it represents an important step within the cascade of charge-transport phenomena 28,29 that result in the photorefractive effect, [30][31][32][33] allowing for a variety of photorefractive phenomena in various photovoltaic ferroelectrics. 34 Due to the application of continuous-wave laser light, a phenomenological description of the photovoltaic effect served convincingly over the last decades.…”

All-optical synchronization for quantum networking

“…For this particular experiment, the SHG up-conversion stages consist of AR coated, bulk magnesium-doped PPLN (MgO:PPLN) crystals (Covesion). Traditionally, undoped PPLN devices (bulk or waveguide structure) suffer greatly from photorefractive effect [Buse et al 2007,Kashin et al 2011 due to their intrinsic properties of large electro-optic coefficient, strong photo-voltaic effect, and strong space charge field. Contrarily to undoped PPLN devices, 5% of magnesium are added to lithium niobate in order to make the crystal more resistance against such effect, hence higher damage threshold.…”

Intra-Cavity Nonlinear Frequency Conversion with Cr3+-Colquiriite Solid-State Lasers

“…In last years, periodically-poled stoichiometric lithium tantalate (PPSLT) has been paid much attention due to its resistance to photorefractive damage and laser damage (Buse et al, 2007;Skvortsov et al, 1993) compared with other similar ferroelectric materials as congruent lithium tantalate (CLT) and congruent or stoichiometric lithium niobate (CLN or SLN, respectively). These properties should be specially taken into account in intracavity configurations, where powers confined in the nonlinear crystal can raise high values.…”