P. Bourson

The composition dependence of the Raman spectrum and new assignment of the phonons in

The Raman spectrum of has been measured for various scattering configurations in crystals with different compositions. The comparison between spectra recorded for the congruent and the nearly stoichiometric crystals shows significant differences in the shape and the number of Raman peaks. The analysis of results leads to a new and complete assignment of the long-wavelength optical phonons in .

Lattice site of Mg ion in LiNbO3 crystal determined by Raman spectroscopy

The defect structure of Mg-doped lithium niobate crystals was studied with varying Mg doping concentration by means of Raman scattering measurements. The Mg content dependences of both the frequency and damping of the two lowest-frequency A1(TO) phonon modes were used to derive the Mg incorporation mechanism in the LiNbO3 lattice. Results indicated that Mg ions are located on the Li site for low doping and then replace both Li and Nb ions for larger concentration.

Optical damage resistance in undoped LiNbO3 crystals

Abstract Photo-induced birefringence changes are investigated on several undoped LiNbO 3 crystals as a function of laser-irradiation time and intensity. Comparison points out that the changes are the smallest in the crystals grown from high temperature top seeded solution (TSS). It is concluded that the optical damage resistance in undoped LiNbO 3 crystals is increased with a decrease of the amount of intrinsic defects related to the non-stoichiometry. The necessity to carefully control the true crystal composition is stressed.

Raman spectroscopy as a probe of the rare-earth ions location in LiNbO3 crystals

Abstract The LiNbO 3 crystals doped with Nd 3+ , Dy 3+ and Er 3+ ions were investigated by means of Raman scattering measurements. Data were compared with results recorded in undoped congruent crystal and highly Mg-doped samples. The doping dependence of frequency and damping in the E(TO 1 ) and the two lowest frequency A 1 (TO) phonon modes were employed to deduce the incorporation site of rare earth doping ions in LiNbO 3 lattice.

Characterization of short-range heterogeneities in sub-congruent lithium niobate by micro-Raman spectroscopy

The spectral widths of Raman lines in nominally pure lithium niobate are measured as a function of the cationic molar ratio, in a wide range from stoichiometry (50 mol% Li) to sub-congruent compositions (below 48.6 down to 47 mol% Li). The broadening observed on the sub-congruent side follows the same slopes as on the congruent-to-stoichiometric side. It is shown that micro-Raman analysis permits one to characterize short-range heterogeneities at the micron scale, such as growth striations in bulk crystals or lithium out-diffusion in the surroundings of titanium-diffused waveguides, with a typical accuracy of 0.04 mol%.

Experimental Study of NaCl Aqueous Solutions by Raman Spectroscopy: Towards a New Optical Sensor

Raman spectroscopy was used to study the NaCl aqueous solutions around the solid-liquid phase transition. Special attention was devoted to the modification induced by the salt on the OH stretching band of water. Investigations were carried out in the temperature range between-21 and 10 °C, for concentrations from 0 to 200 g/L. We demonstrated that micro-Raman spectroscopy can be used as a marker, allowing the determination of the salt concentration of an aqueous solution with an error close to ±5%.

Microstructure and defects probed by Raman spectroscopy in lithium niobate crystals and devices

Raman microprobe applied on LiNbO3 (LN) crystals and derived materials or devices is shown to be a tool to detect either local variations or changes of the whole structure. Position, width, or intensity of one Raman line can be used as markers of a structural change. Indeed, each Raman line can be assigned to a peculiar ionic motion and is differently sensitive to application of strain, temperature change, and electric field. Some vibrational modes are especially associated to the site of Li ion, or Nb ion, or still oxygen octahedron, so that they can be affected by the introduction of dopant ion on one or another site. Therefore, Raman Spectroscopy (RS) can be used as a site spectroscopy to describe the mechanism of doping incorporation in the LN lattice, allowing the optimization of some linear and non-linear optical properties according to the dopant concentration and substitution site. The composition or the content of non-stoichiometry related defects could be derived from the width of some lines. Any damage or local disorder can be detected by a line broadening. The quality or preservation of the structure after chemical treatment, or laser pulses, can be thus checked. The structure of ion-implanted or proton-exchanged wave-guides and periodically poled lithium niobate as well can be imaged from frequency shift or intensity change of some lines. RS is thus a useful way to control the structure of LN and/or to optimize the preparation parameters and its properties.

Raman Study of Neutral and Charged Domain Walls in Lithium Niobate

In this work, we demonstrate the application of micro-Raman spectroscopy for the investigation of the neutral and charged domain walls in the congruent and MgO-doped lithium niobate single crystals. We present local changes of the intensity and frequency of three Raman lines in the vicinity of the domain walls and discuss the influence of the bulk screening of depolarization field on these parameters.

Luminescence of in lithium niobate: influence of the chromium concentration and crystal composition

The luminescence spectrum of Cr 3C in LiNbO3 has been investigated, especially in the R-line range from 7200 up to 7500 ˚ A. For this, we have studied several chromium-doped LiNbO3 crystals with various Li/Nb ratios and different doping concentrations. In addition to the lines which were previously reported, several new peaks were detected in our investigations. In fact, the structure, the shape and the relative intensity of each line are shown to be strongly dependent on the content of doping and on the intrinsic defects related to the non-stoichiometry of the crystal. Among all peaks, we focus our attention on four main lines, which can be separated into two groups, according to their behaviours. The contribution of the first group to the whole spectrum diminishes with increasing Li/Nb ratio so that it vanishes for the stoichiometric composition. The second group of lines, occurring at higher wavelengths, is reported for the first time and is shown to be closely related to the Li/Nb ratio, especially when approaching the stoichiometric composition. These lines exhibit a similar behaviour with increasing Li/Nb ratio or Cr concentration. An explanation of the possible origins of these four peaks is given.

Raman Probe on PPLN Microstructures

We analyse the Raman spectrum recorded during scanning across the domain walls of a periodically poled lithium niobate single crystal. We show that the intensity of scattered light is sensitive to the stresses and electric fields in the vicinity of domain walls. These features are amplified due to large elasto-optic and electro-optic coefficients of lithium niobate.