Marc Dussauze

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.

Fluorescence and second-harmonic generation correlative microscopy to probe space charge separation and silver cluster stabilization during direct laser writing in a tailored silver-containing glass

We report on fluorescence and second-harmonic generation correlative microscopy of femtosecond direct laser-induced structures in a tailored silver-containing phosphate glass. We compare the spatial distributions of the related permanent electric field and silver clusters. The latter appear to be co-localized where the associated electric potential ensures favorable reduction-oxidation conditions for their formation and stabilization. Space charge separation is shown to occur prior the cluster formation. The associated electric field is a key parameter for silver clustering, thanks to electric field assisted silver ion motion. Future photonic structures combining 3D laser-structured fluorescence and nonlinear optical properties in such tailored glass will require an optimal control of the induced electric field distribution.

Correlation between second-order optical response and structure in thermally poled sodium niobium-germanate glass

We have carried out Raman and second harmonic generation (SHG) measurements to probe thermal poling-induced phenomena in glass 20Na2O-80[0.35Nb2O5-0.65GeO2]. A SHG response of 0.6 pm/V was measured after poling in a ∼3 μm thick layer under the anode and found to deviate from the widely used electric field-induced SHG model. This effect was associated with complex structural rearrangements in the subanode layer involving destruction of nonbridging oxygen atoms, formation of molecular oxygen, and enhancement of cross-linking in the glass network.

Enhanced Raman scattering in thermally poled sodium-niobium borophosphate glasses

Micro-Raman analysis has been carried out on the cross section of thermally poled sodium-niobium borophosphate glasses. We were able to measure with accuracy an enhanced Raman response from the nonlinear optical (NLO) layer formed at the anode side of the poled glasses. The thickness of the NLO layer has been estimated. Several spectral changes were observed within this layer, which manifest important structural rearrangements after thermal poling. Possible mechanisms leading to structural reorganization in the space charge region are discussed.

Structure and optical properties of amorphous lead-germanate films developed by pulsed-laser deposition

Lead-germanate materials are attractive systems for photonics applications. In this context, amorphous lead-germanate films were grown by pulsed-laser deposition at different substrate temperatures and oxygen pressures using a glassy target of composition 0.4PbO-0.6GeO(2). Optical and infrared measurements showed that the substrate temperature has a strong influence on the optical quality and stability of the deposited films. An accurate characterization of films was achieved by comparing experimental and simulated transmittance spectra in the infrared, and allowed to probe the structural evolution and variations in composition as a function of oxygen pressure. The results showed that the difference in reactivity of lead and germanium toward oxygen in the laser-produced plasma allows for composition adjustments in the lead-germanate films by varying the oxygen pressure in the deposition chamber.

Large second order optical nonlinearity in thermally poled amorphous niobium borophosphate films

Thin films of sodium niobium borophosphate glass were deposited on silicon wafer and borosilicate glass substrates by radio frequency sputtering. Thermal poling of the films was performed under various voltage conditions. The chemical composition of the films after poling was controlled by x-ray energy dispersive spectroscopy and compared to the initial composition. The second harmonic signals generated by thermal poling were analyzed in reflection mode. The recorded complex Maker fringes pattern signals were simulated and fitted using a multilayer model for the estimation of the second harmonic generation nonlinear coefficients χ(2). The results are compared to previously published χ(2) coefficients obtained for bulk oxide glasses (∼3pm∕V, approximately fourfold as strong as the highest value reported in thermally poled fused silica). Resulting from this study thermally poled niobium sodium borophosphate thin films are revealed of real interest as potential electro-optic devices.

Femtosecond single-beam direct laser poling of stable and efficient second-order nonlinear optical properties in glass

We depict a new approach for the localized creation in three dimensions (3D) of a highly demanded nonlinear optical function for integrated optics, namely second harmonic generation. We report on the nonlinear optical characteristics induced by single-beam femtosecond direct laser writing in a tailored silver-containing phosphate glass. The original spatial distribution of the nonlinear pattern, composed of four lines after one single laser writing translation, is observed and modeled with success, demonstrating the electric field induced origin of the second harmonic generation. These efficient second-order nonlinear structures (with χeff(2) ∼ 0.6 pm V−1) with sub-micron scale are impressively stable under thermal constraint up to glass transition temperature, which makes them very promising for new photonic applications, especially when 3D nonlinear architectures are desired.

Polarization mechanisms and structural rearrangements in thermally poled sodium-alumino phosphate glasses

Thermally poled glasses of composition 0.20Na2O–0.15Al2O3–0.65P2O5 were investigated by second harmonic generation (SHG) to characterize the induced second order optical nonlinearities (χ2), and by infrared reflectance and micro-Raman spectroscopy to probe structural rearrangements in the nonlinear optical (NLO) layer. The SHG signals showed anodic and bulk χ2 contributions, with the anodic response being one order of magnitude stronger. Also, a good agreement was found between the thickness of the NLO anodic layer (approximately 3 μm) and the depth where structural changes were detected. The latter include the destruction of bonds between phosphorus and nonbridging oxygen atoms, this process leads to the release and migration of sodium cations and oxide anions and to the enhancement of glass network connectivity in the anodic NLO layer.Thermally poled glasses of composition 0.20Na2O–0.15Al2O3–0.65P2O5 were investigated by second harmonic generation (SHG) to characterize the induced second order optical nonlinearities (χ2), and by infrared reflectance and micro-Raman spectroscopy to probe structural rearrangements in the nonlinear optical (NLO) layer. The SHG signals showed anodic and bulk χ2 contributions, with the anodic response being one order of magnitude stronger. Also, a good agreement was found between the thickness of the NLO anodic layer (approximately 3 μm) and the depth where structural changes were detected. The latter include the destruction of bonds between phosphorus and nonbridging oxygen atoms, this process leads to the release and migration of sodium cations and oxide anions and to the enhancement of glass network connectivity in the anodic NLO layer.

Towards second-harmonic generation micropatterning of glass surface

Thermal poling of sodium borophosphate niobium glasses, previously coated with a thin silver layer micropatterned by femtosecond laser irradiation, is demonstrated. The field-assisted ion-exchange process for fabricating planar surface in this glass substrate is analyzed. Inside the silver ablated lines obtained by femtosecond laser irradiation, we clearly observe a change in the distribution of the frozen electrostatic field that is modulated by the Ag+/Na+ ion-exchange process during the thermal poling.

Properties and structural investigation of gallophosphate glasses by 71Ga and 31P nuclear magnetic resonance and vibrational spectroscopies

The structure and optical properties of new gallophosphate glasses in the pseudo-binary system xGa2O3 − (100 − x) NaPO3 (x = 0 to 30 mol%), have been investigated. The effect of the progressive addition of Ga2O3 on the local glass structure has been evaluated using Raman and infrared spectroscopies, and 71Ga and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. 71Ga MAS NMR spectra collected at ultrahigh magnetic field (21.1 T) and fast spinning rates (60 kHz) permit the quantification of gallium in 4-, 5- and 6-fold coordination as a function of the Ga2O3 concentration. At low concentrations of Ga2O3, high-coordinate gallium coordinates to oxygens associated with the phosphate chains, increasing the dimensionality and strengthening the glassy network. At moderate Ga loadings, tetrahedral Ga is incorporated into the phosphate chains, introducing additional branching sites which further enhances network connectivity. Higher Ga2O3 content results in the formation of Ga–O–Ga bonds, thereby inhibiting glass formation. 31P MAS NMR and Raman and infrared spectroscopies provide complementary information about the distribution and connectivity of the phosphate groups within the glass network, supporting a structural model which is correlated with the measured optical and thermal properties of the Ga2O3–NaPO3 glasses as a function of the Ga2O3 concentration.