J. Bouillot

Lithium iodate nanocrystals in Laponite matrixfor nonlinear optical applications

A Laponite clay-based lithium iodate nanocomposite have been synthesized for nonlinear optical applications. After addition of lithium iodate aqueous solution to a colloidal suspension of Laponite JS, thin layers are elaborated from this sol using dip-coating technique. After drying and heat treatments between 150 and 220°C, LiIO3 crystallizes in the matrix with nanometer size. As a result of their strong dipolar moment, the LiIO3 crystals can be orientated under an external electric field during nucleation. Planar waveguides have been elaborated on glass substrates and studied using m-lines spectroscopy. The experimental nonlinear optical response has been compared to predictions of a model and an effective nonlinear coefficient deff=1.4pm∕V has been measured.

Characterization of planar waveguides obtained by proton exchange in lithium iodate

Abstract Due to its non-linear optical properties, lithium iodate is commonly used in optical devices. By proton exchange, performed by immersing z -cuts LiIO 3 single crystals in a molten hydrated nitrate salt, we formed a solid solution Li 1− x H x IO 3 layer close to the surface. This modification of the structure increases the refractive index so that a waveguide is created. The index profile obtained by m-lines spectroscopy combined with structure characterization by μ-Raman and X-ray diffraction experiments allows us to describe the diffusion process of hydrogen in LiIO 3 .

LiIO3: growth and properties for optical and photoluminescent applications

Abstract Lithium iodate crystals (α-LiIO3) exhibit large piezoelectric, elasto-optic and non-linear optical effects. Indeed, the high non-linear coefficients of this material make it very useful for second harmonic generation and frequency mixing (d31 and d33 lying between −6 and −7×10 −12 V −1 m for wavelength between 1.06 and 2.12 μm ) [1] , [2] . Moreover, its very large transparency range [3] from 300 nm to 5 μm is very interesting for applications in the IR range. Our present studies concern physical characterizations of this material: • the phase transitions versus temperature have been studied by differential thermal analysis, thermogravimetry and X-ray measurements [4] ; • dielectric measurements versus temperature, by using the impedance spectroscopy technique, have led to a better understanding of the ionic conduction process occurring in α-LiIO3 [5] and optical applications: • waveguides have been realized in this material by ionic (H+) implantation [6] ; • photoluminescence studies have been performed in Cr3+ doped crystals. After a short description of the growth technique, results concerning photoluminescence are developed.

Relaxation phenomena in lithium iodate crystals

Abstract Ionic conductivity of lithium iodate crystals grown in various conditions has been studied in the polar c-axis direction. The dielectric response at room temperature is associated with relaxation of space charges. The temperature dependence of the dc ionic conductivity shows quite different activation energies in the range 35–470 K which are well related to the doping and acidity of the growth solution.

Orientation of LiIO3 Nanocrystals in Laponite Matrix for Periodically Structured Non-Linear Waveguides

Abstract A new clay-based nanocomposite has been developed for non-linear optical waveguiding applications. Thin layers are deposited on glass substrates by using dip coating technique from an aqueous solution made of a Laponite suspension mixed with a lithium iodate (LiIO3) aqueous solution. Transparent layers with waveguiding properties are obtained with an effective non-linear coefficient of about 1.4 pm/V for a 55% vol. LiIO3 composite. Control of nanocrystals orientation has been performed by applying an electric field with Corona discharge or deposited gold electrodes. Characterisation of nanocrystals orientation was done by Second Harmonic Generation (SHG) measurements and polarised light optical microscopy.

SFM and EFM Studies on a Clay-Based Dielectric Nanocomposite

Abstract A Laponite clay-based lithium iodate nanocomposite has been synthesized for non-linear optical applications. The surface morphology of dip-coated optical waveguides were analysed by Scanning Force Microscopy (SFM) techniques. Individual Laponite particles were first imaged by using Intermittent-Contact Atomic Force Microscopy on pure Laponite layers. Electrostatic Force Microscopy was then used on nanocomposite waveguides in order to obtain a “chemical contrast” of sample surface. The strong electrical contrast observed was attributed to sample topography and not to the different properties of each nanocomposite constituent. Finally, in ambient conditions, dip-coated layers were also shown to be sensitive to humidity which leads to the occurrence of surface lithium iodate crystals with sub-micrometer size.

Safe probe for high electric field measurements

The present study concerns an optical electric field measuring device using a lithium niobate (LiNbO/sub 3/) crystal as sensing medium, without any contacting electrode. Such a device has the advantage of providing a good galvanic insulation of materials and persons. A likely application is electric field measurement near electric power installations (frequency 50-60 Hz). The principle of measurement implements the electro-optical effect in the crystals and results from the way in which polarized light is analyzed after going through the crystal. Experimental setups have been developed in order to both validate the physical principle, and calibrate the probe. Simulations of this device with the finite element method being in good agreement with experiment, the implementation of the probe in the foreseen environment are studied. Then, a probe prototype, for which measurement can be realized far away with optical fibers, is performed. Simulated and experimental results near electric power installations are discussed. The results obtained using the prototype are very promising so far.

Design and optimization of an optical high electric field sensor

The present paper proposes an optical device for measuring low frequency high electric fields using a LiNbO/sub 3/ crystal as sensing medium without any contacting electrode. Simulations have been performed in order to find the best design of the sensing element in the sensor.

Optimization of an optical device for low-frequency electric field measurement

The conventional measurement systems for low frequency (50 - 60 Hz) high electric fields measurement currently lay on active metallic probes which can disturb the measured electric field. The present study concerns an optical device using a LiNbO3 crystal, which is known to be electrooptic, as sensing medium. The experimental set-up uses two electrodes to create the electric field to be measured. The principle of measurement implements the electrooptical effect in the crystal without any contacting electrode and is based on the classical static method in which the polarization of light is analyzed after going through the crystal. In order to minimize thermo-optical effects, the light beam propagates along the optical axis and the electric field is applied perpendicularly to the beam. Thanks to an excellent agreement between simulation with Finite Element Method and experiment, the shape of the crystal and its protection ring are optimized. The crystal used here has a regular octagonal section (radius #1.5 mm) and a length of 8 mm.