1,721,039 research outputs found
A study on the periodicity of periodic poled lithium niobate crystals growth by the off-center Czochralski technique
No full textA systematic study on the role of each growth parameter in the PPLN period and the modification of the domain width across the crystal due to the growth process is presented. We focus our attention to the effect of the random errors in the domain boundary position on the SHG conversion efficiency and show a way of optimizing the growth process in order to achieve the highest SHG conversion efficiency and to establish the tolerances on the fabrication processes
Model of the erbium ion exchange process in lithium niobate crystals
No full textA model based on the Nernst-Planck equations is discussed for the trivalent ion exchange process in lithium niobate crystals. Due to the material anisotropy and the different valence state of the exchanged species, a correction to the ion flux expression is considered to include the strain effects. The model is then used to describe the erbium ion exchange in both X- and Z-cut lithium niobate crystals. In this case, the dopant in-depth profiles measured by secondary ion mass spectrometry are well fitted by the theoretical profiles predicted by the model, supporting its validity. Since the model allows to predict the dopant profile into the substrate, it can be used to tailor the process parameters
High Resolution X-Ray Characterization of Sub-Micron Periodic Domain Structures in Lithium Niobate Crystals
No full textThe High Resolution X-Ray Diffraction technique in the reciprocal space mapping mode is exploited to study sub-micron periodic domain structures in lithium niobate crystals. Periodic satellite structure were detected around the reciprocal lattice points which carry information on the domain period and shape and also on the presence of lattice deformations. Moreover a pronounced diffuse scattering peak was observed, indicating the presence of a random displacement field possibly associated to the presence of randomly distributed structural defect
Quantification of Iron (Fe) in Lithium Niobate by Optical Absorption
No full textA quantitative method, based solely on optical absorption, to determine the total iron (Fe) concentration in Fe : LiNbO3 is proposed. Absorption spectra of several samples doped by thermal diffusion with different concentrations and different [Fe2+]/[Fe3+] ratios show an isosbestic point at 342 nm. At this wavelength the absorption is proportional to the total Fe concentration and does not depend on the oxidation state. Thanks to the large number of samples covering a wide range of concentrations, in this work it was possible to estimate an effective absorption cross-section relating the absorbance of a given sample to its iron content. The main advantage of the proposed method is in its simplicity and the fact that the result does not depend on the reduction degree of the sample. As it is known that the absorbance of Fe:LN at another wavelength (532 nm) gives information on the amount of Fe2+ present in the sample, our method makes it possible to characterize both the total Fe amount and its reduction degree within a single optical absorption measurement
Topographic investigation of ferroelectric domain structures in periodically-poled lithium niobate crystals by a profilometer
No full textA topographic investigation of periodically poled lithium niobate (PPLN) crystals was performed by recording a map of the crystal surface after a selective etching process using a standard profilometer. A procedure to correct for the systematic error introduced by the finite size of the tip is discussed in detail so that the width of ferroelectric domains can be mapped with an estimated tolerance of about 3% along the whole length of the sample. The method is applied to a PPLN structure obtained by the Czochralski off-center technique
On the dynamics of periodically-poled lithium niobate formation by off-center Czochralski technique
No full textThe formation mechanisms which might be responsible for the domain structures observed in periodic-poled lithium niobate crystals grown by the off-center Czochralski technique were investigated varying the process parameters. We show that the periodic inverted domains structure does not maintain the polarization over the whole crystal, as commonly accepted. In particular, a ‘‘separation plane’’ parallel to the growth axis exists and divides the crystal in two halves, each with periodic structure but with opposite domain sequences. A possible explanation of the phenomenon
is presented invoking both the thermoelectric effect fluctuation experienced by the growing crystal
Raman investigation of Fe in - diffused photorefractive waveguides on lithium niobate substrates
No full textLithium niobate crystals doped with iron by thermal diffusion: relation between lattice deformation and reduction degree
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