Frédéric Adamietz

Two‐Way Molecular Switches with Large Nonlinear Optical Contrast

Molecular switches: Highly efficient acido- and photoswitchable frequency doublers (see scheme) based on the indolinooxazolidine core are studied by means of hyper-Rayleigh experiments and quantum-chemical calculations.To optimize the nonlinear optical (NLO) contrast, a series of indolinooxazolidine derivatives with electron-withdrawing substituents in the para position on the indolinic residue have been synthesized. Their linear and nonlinear optical properties have been characterized by UV-visible absorption and hyper-Rayleigh scattering measurements, as well as by ab initio calculations. The two-way photo- or pH-triggered switching mechanism has been demonstrated by comparing the absorption spectra of the zwitterionic and protonated open forms (POF). Hyper-Rayleigh measurements have revealed that the second-order NLO contrast between the closed indolinooxazolidine and the open pi-conjugated colored forms remain very large upon substitution. Theory and measurements show that for the POFs the amplitude of the first hyperpolarizability follows the Hammett parameters of the withdrawing groups. However, because the measurements are performed in resonance, to recover this behavior, elaborate procedures including homogeneous and inhomogeneous broadenings, as well as single-mode vibronic structures are necessary to extrapolate to the static limit.

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.

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.

Planar waveguides formed by Ag + –Na + ion exchange in nonlinear optical glasses: diffusion and optical properties

All-optical communication systems are the subject of intense research related to the integration of nonlinear optical materials. In sodiocalcic borophosphate glasses that contain niobium oxide and exhibit high nonlinear optical indices, planar waveguides have been formed by a Ag(+)-Na(+) ion-exchange technique. WKB analysis has been used to characterize the diffusion profiles of silver ions exchanged in glass substrate samples chemically by an electron microprobe technique and optically by an M-line technique. These methods permit the Ag(+) penetration depth and diffusion profile shape and index profiles to be determined. The results are analyzed and discussed in relation to Ca(2+) concentration and exchange conditions in glasses. The Ag(+) diffusion in these glasses can be almost entirely controlled for index-profile engineering.

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.

Enhancement of second harmonic generation signal in thermally poled glass ceramic with NaNbO3 nanocrystals

Glass ceramic composites were prepared by bulk crystallization of NaNbO3 in sodium niobium borate glasses. A homogeneous bulk crystallization of the NaNbO3 phase takes place during heat treatments that produces visible-near infrared transparent materials with ∼30nm NaNbO3 nanocrystallites. Upon thermal poling, a strong Na+ depleted nonlinear optical thin layer is observed at the anode side that should induce a large internal static electric field. In addition, the χ(2) response of the poled glass ceramic composites increases from 0.2 up to 1.9pm∕V with the rate of crystallization. Two mechanisms may be considered: a pure structural χ(2) process connected with the occurrence of a spontaneous ferroelectric polarization or an increase of the χ(3) response of the nanocrystallites that enhances the electric field induced second harmonic generation process.

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.

Experimental and Theoretical Investigation of the First-Order Hyperpolarizability of Octupolar Merocyanine Dyes

Hyper-Rayleigh scattering experiments and quantum chemical calculations are combined to investigate the second-order nonlinear optical responses of a series of three-arm merocyanine derivatives. They exhibit an octupolar hyperpolarizability response with lower amplitude than crystal violet due to a lower extent of the photoinduced charge transfer and reduced bond length alternation. Strong effects on the second-order optical response measured close to the two-photon absorption level are clearly evidenced; for example, the effective measured polarization ratio deviates below the ideal octupolar value of 3/2 even at very low excitation power. These effects are attributed to two-photon absorption resonance, which we believe modifies dynamically the population of the ground state versus that of the excited state.

Contribution of XAFS analysis to the study of the correlation between optical nonlinearity and the geometry of titanium sites in glasses

Abstract In the context of a general investigation of the nonlinear optical properties of glasses, we report here the effect of introducing TiO 2 in various silicate and borophosphate glass matrixes. A correlation study is carried out between the magnitude of the measured nonlinear indices n 2 of these materials and the local structure around titanium which can be deduced using XAFS analysis. This allows to point out that square-based pyramids are particularly efficient when present in borophosphate glasses.

Crystal growth and optical characterizations of Yb3+-doped LiGd6O5(BO3)3 single crystal: a new promising laser material

Single crystals of a new oxyborate, Yb-LGOB, were obtained by an original flux method and interesting spectroscopic properties of this new laser crystal are reported.