Lattices In Lithium Niobate Research Articles

Структурные исследования кристаллов ниобата лития, легированных церием

In this research the structural characteristics of LiNbO3 : Ce (0.13–2.15 mol. %) samples were studied.The concentration dependences of the unit cell parameters of LiNbO3 : Ce crystals were considered. The mechanism of impurity incorporation and the location of intrinsic defects in a LiNbO3 : Ce crystal (0.43 mol. %) were established. Cerium occupied the vacant lithium position in the lithium niobate lattice.

Рентгенографические исследования сегнетоэлектрических кристаллов ниобата лития, легированных редкоземельными элементами

The lattice structural distortions of LiNbO3 crystals doped with samarium with a concentration of 1.0, 1.9, 2.5 mol. % were studied by X-ray diffraction methods. It was found that the samarium atoms and some of the niobium atoms occupied the vacant positions of lithium in the crystal lattice, and some of the niobium atoms were located in the empty octahedron. The octahedra of SmLiO6 was distorted more strongly than octahedra of NbLiO6 when niobium atoms entered the vacant positions of lithium. The smallest changes in the bond lengths in the octahedra of the main motif and in the defect region as well as along the polar axis in the lithium niobate lattice were observed in the sample with a samarium concentration of 2.5 mol. %.

A Low propagation loss planar waveguide structure fabricated on lithium niobate via low fluence argon-ion irradiation

A low propagation loss waveguide structure was fabricated on lithium niobate crystal using 70 MeV argon-ion irradiation with a low fluence of 1 × 1012 ions/cm2. Guided modes were detected in visible and near-infrared regions; the propagation loss at 633 nm is ∼0.8 dB/cm. meaning this waveguide can be used for visible and near-infrared communications The Raman spectra of the waveguide layer and substrate indicate the lithium niobate lattice structure has been preserved after the low dose argon-ion irradiation. The results indicated that the low fluence Ar-ion can be used for optical waveguide fabrication on lithium niobite crystal.

Spectroscopic properties of trivalent chromium ion in lithium niobate crystals

The formulas of crystal field theory are derived for a particular case of the C3v symmetry group. Convenient and numerically simple methods are proposed to take into account the polarization of the local environment of the Cr3+ impurity ion in LiNbO3. The parameters of intraion interactions for Cr3+ in lithium and niobium positions in the lithium niobate lattice and the distortion of the niobium octahedron in lithium niobate, which is caused by the incorporation of trivalent chromium ion, are determined.

Light propagation in double-periodic nonlinear photonic lattices in lithium niobate

Single- and double-periodic one-dimensional photonic lattices are formed in lithium niobate using both titanium in-diffusion and holographic grating recording. We investigate linear band structures and diffraction properties of such superlattices and observe a decrease of discrete diffraction with increasing modulation depth of the second superimposed lattice. In weakly modulated superlattices with tailored diffraction properties, our results demonstrate the formation of discrete solitons having a propagation constant inside the extra mini-gap formed inside the Brillouin zone.

“Incoherent” generation of spatial gap solitons within one-dimensional photorefractive photonic lattices in lithium niobate

The effect of the formation of spatial gap solitons within one-dimensional optically induced photo-refractive photonic lattices in iron-doped lithium niobate is experimentally investigated. Mutually incoherent Bragg-matched beams with optical powers in the microwatt range from two different He-Ne lasers are used to generate immobile spatial gap solitons within the lattice with a spatial period of 15 μm.

Discrete Diffraction and Spatial Self-Action of Light Beams in One-Dimensional Photonic Lattices in Lithium Niobate

Features of the behavior of light beams in one-dimensional photonic lattices in iron-doped lithium niobate have been experimentally studied. It is demonstrated that bright discrete spatial solitons and bright gap solitons can be formed in this system using 633 nm radiation on a microwatt power level. © 2005 Pleiades Pub- lishing, Inc.

Growth of diamond film on single crystal lithium niobate for surface acoustic wave devices

Single crystalline lithium niobate thin films on diamond are useful for surface acoustic wave devices that operate at gigahertz frequency. The differences in the atomic bonding and crystalline structure between the lithium niobate and diamond and the high interfacial energy were responsible for formation of microcrystalline films of lithium niobate deposited on polycrystalline diamond. We have carried out growth of continuous diamond layer on single crystal lithium niobate by microwave chemical vapor deposition to overcome the above deficiencies. The temperature of the substrate during deposition has been maintained near 700 °C to reduce the loss of lithium from lithium niobate and to reduce the thermal stresses. Characterization by x-ray diffraction and Raman spectroscopy showed that the lithium niobate lattice is preserved without incorporation of carbon and the diamond layer is free from graphitic carbon. The integrated lithium niobate-diamond layered structure is shown to be suitable for surface acoustic wave devices.

On the compositional nature of bulk doped periodic poled lithium niobate crystals

The compositional nature of the Erbium, Neodymium and Yttrium bulk doped periodic poled lithium niobate crystals obtained by the off-centered Czochralski technique has been studied. It has been observed that, in all cases, the impurity concentration is constant along the periodic domain structure. Moreover, it is shown that there exists a periodical variation in the Nb concentration, which is directly related with an inversion in the Li/Nb ratio along the periodic domain structure. The magnitude of the Nb variation seems to depend on the nature of the dopant and its position in the lithium niobate lattice, together with the value of the segregation coefficient of the impurity and the shape of the solid–liquid interface during growth.

Computer simulation of channeling spectra with the cassis program

The recently developed Monte Carlo program CASSIS for the simulation of channeling phenomena was upgraded in order to enable the generation of energy spectra for Rutherford backscattering in channeling conditions. The basic concepts of the module added are described and discussed. The feasibility of the program is demonstrated by comparing experimental and simulation results for simple bulk materials like diamond and silicon as well as for the trigonal lithium niobate lattice. For all three cases excellent agreement between experiment and calculation were obtained. Additionally spectra measured for a fully strained Si0.75Ge0.25 layers on silicon, which show interesting channeling effects, e.g. catastrophic dechanneling were successfully simulated.

Upconversion luminescence properties of Er3+ions doped in lithium niobate single crystals

Abstract Laser selective excitation is used to study the spectroscopic properties of Er3+ ions doped in Lithium Niobate (LNB) single crystals, where it substitutes for the Li+ or Nb5+ sites both having local C3 symmetry. Excited state absorption resulting in energy upconverted fluorescence are observed (for dopant concentrations range 0.045 to 0.37 mol.%) for temperatures up to 297 K. The upconversion mechanism is dominated by the sequential two photon excitation process. The polarised excitation and emission spectra of the upconverted fluorescence reveal the existence of multiple sites and inhomogeneously broadened energy levels as a consequence of the disordered structure of the LNB lattice.

Lattice constants of K- and Mg-doped LiNbO 3. Comparison with nonstoichiometric lithium niobate

The dependencies of lithium niobate lattice constants on stoichiometry and concentration of K and Mg dopants were investigated with the help of X-ray powder diffraction. It was found that in contrast to MgO dopant, an addition of K 2O to the congruent LiNbO 3 melt leads to a decrease of the lattice constants. A similar reduction of a and c parameters is observed if the Li content of the crystal is increased, which is accompanied by an improvement of the lithium niobate lattice structure because of diminishing concentration of intrinsic nonstoichiometric defects.

Diffusion of Aluminum, Scandium and Gallium Ions into Lithium Niobate Single Crystals

Diffusion of aluminum, scandium and gallium ions in single crystals has been studied. Stoichiometric crystals have been grown by the Czochralski method using a double crucible and automatic powder supply system. Diffusant concentration profiles were measured by secondary ion mass spectrometry. The diffusivities of all ions depended on the Li/Nb ratio of single crystals. The diffusion coefficients were larger in the samples with lithium deficient composition than in that with stoichiometric composition. This behavior was explained by a cation vacancy model in the lithium niobate lattice.