Evelyne Fargin

Optical non-linearity in oxide glasses

The origin of the optical non-linear response has been investigated in two different types of oxide glasses. Linear and non-linear refractive indices have been obtained by interferometric measurements. Correlations between the local structure of polarizable entities within glasses and their optical activities have been tentatively established through ab initio calculations.

Correlations between structural properties of Nb2O5NaPO3Na2B4O7 glasses and non-linear optical activities

Abstract Information about the origin of the optical non-linear response in transparent glasses can be gained from a detailed structure investigation using Raman and X-ray absorption spectroscopies. The effects resulting from the introduction of niobium oxide in the sodium borophosphate matrix of composition 0.95NaPO 3 0.05Na 2 B 4 O 7 are described. For small niobium concentrations, the formation of distorted NbO 6 octahedra is observed. The increase of niobium concentration allows the progressive linking of corner-shared and less distorted octahedra. The correlative evolution of the measured third order susceptibilities χ (3) is analyzed on the basis of the bond orbital theory. A good agreement between experimental and calculated χ (3) is obtained as long as the NbO 6 entities are isolated from each other, but the clustering of these entities increases the non-linear response, χ (3) .

Large second-harmonic generation of thermally poled sodium borophosphate glasses

Second harmonic generation (SHG) has been obtained in a rich in sodium niobium orophosphate glass by a thermal poling treatment. The thermally poled glass SHG signal has been studied through an original analysis of both transmitted and reflected polarized Maker-fringe patterns. Therefore, the second order nonlinear optical (NLO) efficiency was estimated from the simulation of the Maker-fringe patterns with a stepwise decreasing profile from the anode surface. A reproducible chi(2) susceptibility value as high as 5.0 +/-0.3 pm/V was achieved at the anode side. The nonlinear layer, found to be sodium-depleted up to 5 microm deep inside the anode side, identical to the simulated nonlinear zone thickness, indicates a complex space-charge-migration/ nonlinear glass matrix response process.

Second harmonic generation optimization in thermally poled borophosphate glasses and characterization by XANES and XPS

Second harmonic generation (SHG) in poled glasses opens new opportunities in material research and device development for optics. SHG results that relate to thermally poled new borophosphate glasses have been analyzed. By a cycling poling–depoling process an optimization of the SHG response can be obtained. As the signal is localized near the surfaces in contact with the electrodes during poling, XPS and X-ray absorption near-edge spectroscopy (XANES) spectroscopies have been performed to characterize cathodic and anodic surfaces of these glasses before poling, and after poling or depoling treatments. Structural differences are observed by XANES at the O K-edge after poling on both surfaces. Moreover, an accumulation of Na+ mobile cations is evidenced on the cathodic surface by XPS spectroscopy confirming the migration of Na+ mobile cations after the glass has been submitted to high dc field. Finally, the XPS and XANES investigations of poled glasses evidences some breakage of phosphate chains in the glass network which occur during the poling treatment. Conversely, bridging bonds are partly restored after thermal depoling.

Precise and absolute measurements of the complex third-order optical susceptibility

We present precise and absolute measurements of full complex third-order optical susceptibility on different fused-silica and original glasses composed of tellurium, titanium, and niobium erbium. These materials are designed to be the key point for applications ranging from high-power laser systems to optoelectronics; their nonlinear index of refraction is a major property and thus must be accurately known. A large dispersion (more than 30%) of the nonlinear index of fused-silica glasses was found. Measurements on tellurium glasses have shown strong nonlinearities, to be linked to the configurations of their cations and anions.

Time-resolved absolute interferometric measurement of third-order nonlinear-optical susceptibilities

A modified Mach–Zehnder interferometer has been built for measurement of nonlinear-optical susceptibilities in bulk materials. Both slow- and fast-intensity-dependent refractive-index changes can be measured in absolute value, with femtosecond time resolution, high sensitivity, and precision, by means of a new fringe-locking technique. Results on fast nonlinearities of CS2 liquid and glasses are presented.

Nonlinear optical properties for TiO2 containing phosphate, borophosphate, and silicate glasses

A theoretical and experimental analysis of the optical properties for titanium-containing glasses is reported. A bond orbital theory elaborated by M. E. Lines [Phys. Rev. B 41, 3372 (1990); 41, 3383 (1990); 43, 11 978 (1991)] for crystals has been extended to these glasses, where the influence of the Ti–O bond environment has been considered. The resulting calculated values obtained for linear and nonlinear indices have been successfully compared with absolute experimental indices independently measured using a Mach–Zehnder interferometer. This agreement involves an adjustment of a local field factor f, varying from 1 to 1.2, which emphasizes the importance of the titanium–oxygen environment particularly upon the nonlinear optical properties of the investigated materials.

Impact of storage induced outgassing organic contamination on laser induced damage of silica optics at 351 nm

The impact of storage conditions on laser induced damage density at 351 nm on bare fused polished silica samples has been studied. Intentionally outgassing of polypropylene pieces on silica samples was done. We evidenced an important increase of laser induced damage density on contaminated samples demonstrating that storage could limit optics lifetime performances. Atomic Force Microscopy (AFM) and Gas Chromatography -Mass Spectrometry (GC-MS) have been used to identify the potential causes of this effect. It shows that a small quantity of organic contamination deposited on silica surface is responsible for this degradation. Various hypotheses are proposed to explain the damage mechanism. The more likely hypothesis is a coupling between surface defects of optics and organic contaminants.

Thermally poled new borate glasses for second harmonic generation

Abstract Second harmonic generation (SHG) in poled glasses opens new opportunities in material research and device development for optics. Within this context (1−x)LaMgB5O10–xTiO2 and (1−x) LaMgB 5 O 10 –x Nb 2 O 5 (0⩽x⩽0.4) glasses have been formed and characterized. The structure of unpoled glasses has been studied by IR, Raman, and XAFS spectroscopies. Optical properties of transmission like linear refractive indexes and third-order non-linear optical susceptibility χ(3) have been investigated. A second harmonic signal was observed for each thermally poled composition, except for the LaMgB5O10 matrix glass.

Evidence of a green luminescence band related to surface flaws in high purity silica glass

Using luminescence confocal microscopy under 325 nm laser excitation, we explore the populations of defects existing in or at the vicinity of macroscopic surface flaws in fused silica. We report our luminescence results on two types of surface flaws: laser damage and indentation on fused silica polished surfaces. Luminescence cartographies are made to show the spatial distribution of each kind of defect. Three bands, centered at 1.89 eV, 2.75 eV and 2.25 eV are evidenced on laser damage and indentations. The band centered at 2.25 eV was not previously reported in photo luminescence experiments on indentations and pristine silica, for excitation wavelengths of 325 nm or larger. The luminescent objects, expected to be trapped in sub-surface micro-cracks, are possibly involved in the first step of the laser damage mechanism when fused silica is enlightened at 351 nm laser in nanosecond regime.