Ziheng Huang

Increased optical-damage resistance in tin-doped lithium niobate

Applications of lithium niobate in nonlinear optics at high light intensities are seriously hampered by optical damage. Recent investigations have shown that Hf(4+) and Zr(4+) ions have some advantages in suppressing optical damage of LiNbO(3) with respect to Mg(2+). Here we present Sn-doped LiNbO(3) (Sn:LN). Experimental results indicate that Sn:LN has similar optical damage resistance to Mg-doped LiNbO(3), but the doping threshold of Sn is only 2.5 mol.%, where its distribution coefficient is 0.98. Hence Sn(4+) ion turns out to be another good choice for increasing optical damage resistance of LiNbO(3).

Influence of composition on the photorefractive centers in pure LiNbO3 at low light intensity.

The influence of composition on the photorefractive effect in pure LiNbO3 crystals at low light intensity was investigated. The experimental results indicate that different defects dominate the photorefractive centers of pure LiNbO3 with various compositions. Bipolarons are considered to be responsible for the enhanced photovoltaic field in reduced near-stoichiometric LiNbO3, and their bulk photovoltaic constant kappa is estimated to be approximately 6.95 x 10(-32) m3/V. Q polarons (composed of two bipolarons) are introduced to explain the photorefractive effect of congruent LiNbO3 at both low and high light intensities.

The relationship between the switching field and the intrinsic defects in near-stoichiometric lithium niobate crystals

Several near-stoichiometric lithium niobate (LiNbO3) plates were prepared by the vapour transport equilibrium technique. Domain reversal was carried out on these samples by electric field poling. A nonlinear dependence of switching field on the concentration of anti-site niobium ( ) ions was observed. This nonlinear relationship was explained by a two-dimensional model based on the dynamics of the domain wall. A parameter of θc, denoting the critical position of the domain wall round ions, was introduced to describe domain reversal. The domain wall energy per unit area for near-stoichiometric lithium niobate was also roughly calculated to be larger than 0.27 J m−2.

Light-induced superlow electric field for domain reversal in near-stoichiometric magnesium-doped lithium niobate

Light-induced domain reversal of near-stoichiometric Mg-doped LiNbO3 crystal was investigated with a focused 532 nm continuous laser beam. The lowest electric field applied to accomplish domain nucleation is only 30 V/mm and 1/80 of the coercive field, which is safe and convenient for us to fabricate domain structures. Under this superlow applied field, the pinning effect of domain wall is so obvious that the inverted domain reveals a gear shape contrary to the hexagon in a higher applied field. Then two-dimensional domain patterns with the smallest domain size of 4 μm have been fabricated.

Determination of the Li/Nb ratio in LiNbO3 crystals prepared by vapor transport equilibration method

Off-congruent lithium niobate (LiNbO 3 ) single crystal was prepared by vapor transport equilibration (VTE). The Li/ Nb ratio was determined by means of indirect methods such as the lattice parameters, the fundamental absorption edge position and the IR vibrational spectrum. Comparison of the results of the VTE LiNbO 3 with those of the congruent crystal and congruent composition melt added 6 wt% K 2 O. In all cases the Li 2 O content was found to be closer to 50% than that of the congruent composition melt added 6 wt% K 2 O. The homogeneity of the composition in the crystal was also investigated. The data presented in this work show that the VTE method can be effectively applied to produce LiNbO 3 stoichiometric crystal.

Investigations of centers formed in UV-light-induced absorption for LiNbO3 highly doped with Mg and Hf

UV-light-induced absorption in LiNbO(3) highly doped with Mg and Hf was investigated. Distinct decay behavior was attributed to the different centers formed under UV illumination, i.e., the shallow and intermediate deep centers for trapping holes. O- formed near doped cation at the niobium site was suggested to be the origin of the shallow center, whereas that formed near cation vacancy was suggested to be the origin of the intermediate deep center. The influence of the sample status (oxidized or reduced) on the UV-light-induced absorption was demonstrated to support our suggestion. Two different dark decay processes were associated with relaxations of holes from the shallow centers to two unequivalent Nb(Nb) adjacent to the doped cations at niobium sites.

The electrostatic depinning mechanism of domain wall for near-stoichiometric lithium niobate crystals

We studied theoretically the pinning?depinning transition of the domain wall on the surface of near-stoichiometric lithium niobate (NSLN) crystals. Based on the analysis of electrostatic interaction between the electrode and the sample surface, the detailed depinning mechanism of the domain wall at the pinning defect was shown. Using the classical shell-model, the critical parameter ?c for the domain wall at the reversal of was estimated to be 11? and the domain wall energy per unit area for NSLN crystals was also calculated roughly as 1.3?J?m?2.

Photochromic effect in LiNbO(3): Fe :Co.

In this paper, Co(2)O(3) was codoped in LiNbO(3): Fe crystals. It was found that Co codoping can give rise to the strong photochromic effect in LiNbO(3): Fe. Based on the UV-VIS-NIR absorption spectra, photorefractive sensitivities, and EPR results for both virgin and sensitized states of the crystal, the photochromic mechanism in this material was suggested as follows. During sensitization, electrons transfer from O(2-) to Fe(3+) directly while holes are thermally excited from O- into the valence band and then partly trapped by Co(2+), which leads to the darkening of the crystal. In bleaching process, the electrons are excited from Fe(2+) to the conduction band by green light and recombine with the holes on the Co(2+) level. Sensitizing/bleaching experiments were also carried out in LiNbO(3): Fe: Co crystals. Fast sensitization found for this material is beneficial to two-color recording.