Á. Péter

Growth of stoichiometric LiNbO3 single crystals by top seeded solution growth method

Abstract Stoichiometric LiNbO 3 single crystals have been grown using the top-seeded solution growth method from potassium containing flux. Spectroscopic properties (e.g. the UV absorption edge, OH-vibrational band) have been used for the characterization of the crystal composition. Optical homogeneity and the formation of lattice defects were compared with those of undoped off-congruent composition crystals prepared by the Czochralski method.

Temperature dependence of the absorption and refraction of Mg-doped congruent and stoichiometric LiNbO3 in the THz range

The absorption coefficient and the index of refraction of Mg-doped LiNbO/sub 3/ crystals with different compositions are determined in the 30 - 200 cm-1 frequency range. We find that stoichiometric LiNbO/sub 3/ has smaller absorption and index of refraction than congruent samples.

Growth and properties of Bi2TeO5 single crystals

The authors report the successful growth of Bi2TeO5 single crystals by the Czochralski method. This crystal is a new prospective piezoelectric material. Boules as large as 25 mm diameter and 50 mm length were grown, providing pale yellow, optically transparent specimens suitable for indepth physical investigations.

Nonlinear refraction and absorption of Mg doped stoichiometric and congruent LiNbO3

The light induced change of refraction is studied in pure and Mg doped LiNbO3 with congruent and stoichiometric compositions by the Z-scan method using all-lines visible argonion laser, up to MW/cm2 intensity level. In Mg-doped congruent and stoichiometric crystals with Mg concentrations above threshold a positive change in the refractive index was found, in contrast to all other cases where beam fanning and negative change of the refractive index were observed. The beam distortion in the samples doped above threshold was related to thermal lensing, while below it to the photorefractive effects. It was also shown that for thermal lensing nonlinear absorption plays a dominant role. The Z-scan method was found to be an alternative technique to decide whether the Mg dopant level is above or below the photorefractive threshold. The damage resistance of the Mg doped samples above threshold was higher for the stoichiometric crystal than for the congruent one and increased with the amount of the built-in Mg conc...

Investigation of the photorefractive effect in Bi2TeO5

Single crystals of Bi2TeO5, both undoped and doped with transition‐metal‐ion dopants, were grown with high optical quality. Continuous‐wave four‐wave‐mixing experiments on these crystals show a strong photorefractive signal with a multicomponent decay. The photorefractive efficiency was studied as a function of the wavelength, intensity, polarization direction, and crossing angle of the laser write beams, and the sample orientation. Both absorption and phase gratings were observed with their relative strengths dependent on the laser wavelength and sample dopants. The signal evolves in time from a defect population grating, to trapped charge gratings involving two different types of traps, to fixed gratings produced by oxygen ion displacements. The photorefractive effect in this material is found to be of the photoconductive type and it produces a larger diffraction efficiency than that observed in sillenite materials under the same experimental conditions. A mechanism is proposed for the various physical ...

Dopants in photorefractive bismuth tellurite Bi2TeO5 crystals

Bi2TeO5 is a new nonlinear optical crystal with interesting photorefractive properties. A photorefractive grating that was written into a sample more than four years ago is still measurable. The present investigation was directed to different dopants that were expected to modify the optical and photorefractive properties of the crystal. Method of the analysis and the distribution coefficients are presented for Cr, Mo, V, Fe, Ni, and Cu dopants. The influence of the specific dopants on various characteristics is discussed.

Measurement of laser-induced refractive index changes of Mg-doped congruent and stoichiometric LiNbO3

Light-induced refractive index changes and nonlinear absorption of undoped and Mg-doped LiNbO3 with congruent and stoichiometric composition were investigated by the Z-scan method using an all-visible argon-ion laser with intensities up to the MW/cm2 level. Charge coupled device recordings demonstrate that the Z-scan method is suitable for quantitative study of Mg-doped samples, while it can be used only for qualitative measurements of undoped samples because of beam fanning in the latter case. Stoichiometric LiNbO3 doped with 5 mol % Mg shows positive refractive index changes opposite to those in cases of undoped congruent, undoped stoichiometric and 5 mol % Mg-doped congruent LiNbO3. The refractive index change of Δne=2.5×10−5 measured at 0.37 MW/cm2 light intensity for stoichiometric LiNbO3:Mg is six times smaller than that of congruent LiNbO3:Mg at 0.1 MW/cm2.

Refractive index changes in Mg-doped LiNbO3 caused by photorefraction and thermal effects

The origin of light-induced refraction changes in Mg-doped congruent and stoichiometric LiNbO3 (LN) has been investigated using the Z-scan method. The limitations of this method are discussed. We showed that in 5 mol% Mg-doped congruent LN photorefraction (PR) dominates among the nonlinear effects at the MW cm−2 light intensity level. For 2–5 mol% Mg-doped stoichiometric samples at the same intensity level PR are absent as shown by CCD recordings of the beam cross section, the sign of the changes and the excellent fitting of the Z-scan curves. From the magnitude and the intensity dependence of the measured nonlinear refraction of the Mg-doped stoichiometric crystals we concluded that a thermal effect is responsible for the changes observed. The thermally induced refractive index changes are associated with nonlinear absorption.

Revealing growth defects in non-linear borate single crystals by chemical etching

Abstract Inorganic cyclic borates such as β-BaB 2 O 4 (BBO), LiB 3 O 5 (LBO), CsLiB 6 O 10 (CLBO) and Li 2 B 4 O 7 (LTB) are excellent non-linear optical (NLO) materials, particularly in the ultraviolet region. Another type of borate is YAl 3 (BO 3 ) 4 (YAB) which is utilized as a laser host and for self-frequency doubling. Growth imperfections causing scattering and absorption of laser beams affect the performance and the use of borate single crystals. Defects, like inclusions, twins, grain boundaries and dislocations form readily in crystals grown by both the high temperature top-seeded solution growth (HTTSSG) method (BBO, LBO, YAB) and the Czochralski technique (CLBO, LTB). Chemical etching methods have been developed on various planes of the different borate crystals, in order to reveal the nature and the distribution of these defects. These methods have successfully been used to characterize NLO borate crystals. The origins of lattice defect formation are discussed in terms of the growth parameters.

IR absorption spectroscopy of water in CsLiB6O10 crystals

AbstractPolarized absorption spectra of CsLiB 6 O 10 crystals have been measured between )186 and 25 C in the 1500–7500cm 1 wavenumber range. A series of absorption bands have been observed with intensities depending on the thermalhistory of the crystals. Three of them have been assigned as the fundamental H–O–H bending mode (d ¼ 1650 cm 1 ),and symmetric and asymmetric OH stretching modes of the bound H 2 O molecule (m s ¼ 3413 cm 1 and m a ¼ 3581 cm 1 ,respectively). Additional features in the 3800–4400, 4700–5300 and 6500–7100 cm 1 ranges have been interpreted asovertones and combinations of the fundamental H 2 O vibrations. The above assignments have been verified by detectingthe isotopic replica of the bands in a crystal treated in D 2 O vapour atmosphere. The possible sites for the H 2 O moleculein the lattice have been deduced from polarization angle dependence measurements. 2003 Elsevier B.V. All rights reserved. PACS: 42.70.Mp; 61.72.)y; 78.30.HvKeywords: FTIR spectroscopy; H