Christine Galez

Harmonic nanocrystals for biolabeling: a survey of optical properties and biocompatibility.

Nonlinear optical nanocrystals have been recently introduced as a promising alternative to fluorescent probes for multiphoton microscopy. We present for the first time a complete survey of the properties of five nanomaterials (KNbO(3), LiNbO(3), BaTiO(3), KTP, and ZnO), describing their preparation and stabilization and providing quantitative estimations of their nonlinear optical response. In the light of their prospective use as biological and clinical markers, we assess their biocompatibility on human healthy and cancerous cell lines. Finally, we demonstrate the great potential for cell imaging of these inherently nonlinear probes in terms of optical contrast, wavelength flexibility, and signal photostability.

Nano-FROG: Frequency Resolved Optical Gating by a nanometric object

We present a technique to characterize ultrashort pulses at the focal plane of a high numerical aperture objective with unprecedented spatial resolution, by performing a FROG measurement with a single nanocrystal as nonlinear medium. This approach can be extended to develop novel phase-sensitive techniques in laser scanning microscopy, probing the microscopic environment by monitoring phase and amplitude distortions of femtosecond laser pulses.

Characterization of the nonlinear optical properties of nanocrystals by Hyper Rayleigh Scattering

BackgroundHarmonic Nanoparticles are a new family of exogenous markers for multiphoton imaging exerting optical contrast by second harmonic (SH) generation. In this tutorial, we present the application of Hyper-Rayleigh Scattering (HRS) for a quantitative assessment of the nonlinear optical properties of these particles and discuss the underlying theory and some crucial experimental aspects.MethodsThe second harmonic properties of BaTiO3, KNbO3, KiTiOPO4 (KTP), LiNbO3 and ZnO nanocrystals (NCs) are investigated by HRS measurements after careful preparation and characterization of colloidal suspensions.ResultsA detailed analysis of the experimental results is presented with emphasis on the theoretical background and on the influence of some experimental parameters including the accurate determination of the nanocrystal size and concentration. The SH generation efficiency and averaged nonlinear optical coefficients are then derived and compared for six different types of NCs.ConclusionsAfter preparation of colloidal NC suspensions and careful examination of their size, concentration and possible aggregation state, HRS appears as a valuable tool to quantitatively assess the SH efficiency of noncentrosymmetric NCs. All the investigated nanomaterials show high SH conversion efficiencies, demonstrating a good potential for bio-labelling applications.

Nonlinear optical and magnetic properties of BiFeO3 harmonic nanoparticles

Second Harmonic Generation (SHG) from BiFeO3 nanocrystals is investigated for the first time to determine their potential as biomarkers for multiphoton imaging. Nanocrystals are produced by an auto-combustion method with 2-amino-2-hydroxymethyl-propane-1,3-diol as a fuel. Stable colloidal suspensions with mean particle diameters in the range 100–120 nm are then obtained after wet-milling and sonication steps. SHG properties are determined using two complementary experimental techniques, Hyper Rayleigh Scattering and nonlinear polarization microscopy. BiFeO3 shows a very high second harmonic efficiency with an averaged 〈d〉 coefficient of 79 ± 12 pm/V. From the nonlinear polarization response of individual nanocrystals, relative values of the independent dij coefficients are also determined and compared with recent theoretical and experimental studies. Additionally, the particles show a moderate magnetic response, which is attributed to γ-Fe2O3 impurities. A combination of high nonlinear optical efficiency and magnetic response within the same particle is of great interest for future bio-imaging and diagnostic applications.

Design and optimization of a low frequency electric field sensor using Pockels effect

The present paper proposes an optical device for measuring low-frequency (50-60 Hz) high electric fields (0-200 kV.cm/sup -1/) using a LiNbO/sub 3/ crystal as sensing medium without any contacting electrode. Thus, a good galvanic insulation of material and person is obtained. An experimental setup is developed in the laboratory by using the electro-optical effect or Pockels effect, and several measurements are realized. Simulations are performed with the finite element method (FEM) to optimize the sensing medium of the device. Experimental and simulation results are presented and discussed. The sensor induces a weak disturbance of the local electric field to be measured. The sensibility of the sensor is about 4 /spl mu/A/(kV.cm/sup -1/).

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.

Electrical conductivity of α-LiIO3 acid type crystals at 1 kHz

Abstract The temperature dependence of the electrical conductivity of α-LiIO3 acid type crystals is studied. By applying a very low amplitude electric field at 1 kHz and performing a continuous sampling of measurements, differences, reproducible for all the investigated samples, appeared between the first and subsequent heatings The anomalies occurring during the first heating are attributed mainly to inclusions of mother liquor, HIO3 and Li1-xHxIO3. The ‘intrinsic’ conductivity is measured after a first annealing at about 470 K; the activation energies are then calculated.

Second-Harmonic Generation Imaging of LiIO3/Laponite Nanocomposite Waveguides

We have developed LiIO3/laponite nanocomposite thin films to form waveguides with quadratic nonlinear optical properties. The films are dip-coated and annealed to induce LiIO3 crystallisation within the laponite matrix. LiIO3 nanocrystal orientation can be controlled using an electric field during the annealing process. In this article we perform the characterisations of the nanocomposite films through m-line spectroscopy and second harmonic generation microscopy (SHGM). Both refractive indexes deduced from m-line spectra and the SHG signal are shown to depend on the nanocrystal orientation distribution, and a relationship between the optical properties and microscopic structure of the films is developed.

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.