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The coherent photogalvanic effect leads to the generation of a current under the absorption interference of coherent beams and allows for the inscription of space‐charge gratings leading to a second‐order susceptibility (χ(2)). The inscribed grating automatically results in quasi‐phase‐matching between the interfering beams. Theoretical and experimental studies, considering the degenerate case of second‐harmonic generation, show significant conversion efficiency enhancements. However, the link between the theory and experiment is not fully established such that general guidelines and achievable conversion efficiency for a given material platform are still unclear. In this work, the phenomenological model of coherent photogalvanic effect in optical waveguides is theoretically analyzed. This model predicts the existence of non‐degenerate sum‐frequency generation quasi‐phase‐matching gratings, which is confirmed experimentally for the first time. Furthermore, the time dynamics of the space‐charge grating inscription in coherent photogalvanic process is formulated. Based on the developed theoretical equations, the material parameters governing the process for stoichiometric silicon nitride are extracted. The results obtained provide a basis to compare the performances and potentials of different platforms. This work not only supplements the theory of coherent photogalvanic effect, but also enables us to identify critical parameters and limiting factors for the inscription of χ(2) gratings. [ABSTRACT FROM AUTHOR]

The results of electro-optic coefficient measurements performed with three commonly applied techniques used to assess electro-optic coefficients: the Mach-Zehnder, the Teng-Man, and the attenuated total reflectance technique are reported. It is shown that the signal obtained by the Mach-Zehnder and Teng-Man techniques is strongly influenced by the multiple internal reflection and piezo- and electrostrictive thickness change effects, which in our opinion have not been addressed sufficiently in the literature. A novel approach based on using Abelès matrix formalism is implemented for the retrieval of electro-optic coefficients from experimental data. The measurement results, errors, and comparison of the obtained electro-optic coefficient values with the ones expected from the second harmonic generation measurements are discussed. It is demonstrated that, by applying incidence angle scan measurements in Teng-Man technique, an analytic approximation that ignores multiple internal reflection and thickness change effects can provide an electro-optic coefficient estimate within the precision of 2%. This value is much less than the error caused by the thickness change effect that may appear in the attenuated total reflectance technique which inherently has low sensitivity to the thickness modulation effects in the sample. [ABSTRACT FROM AUTHOR]

In this study we report investigationof the polymer film morphologymodifications during their corona poling for fabrication of nonlinearoptically (NLO) active materials. We demonstrate that at certain polingconditions surface and spatial inhomogeneities in the poled area ofthe sample appear. Densities of the inhomogeinities depend on thestrength of the poling field, the sample temperature during the poling,and the prepoling conditions. Optimization of the poling conditionsdirected toward avoiding surface modifications enables us to increasethe overall observable effective nonlinearity of the sample up to10 times. To investigate, understand, and eventually explain the formationof the spatial and surface structure inhomogeinites in the poled materialwe have used optical, second harmonic, and scanning electron microscopemeasurements, as well as the conductivity measurements of the thinfilms. We present results of poled polymer host–guest filmswhere (dimethylamino)benzylidene-1,3-indandione and low dipole moment2,2′,2″-(4,4′,4″-nitrilotribenzylidene)triindan-1,3-dionewere used as guests in poly(methyl methacrylate), polystyrol, andpolysulfone matrixes doped at 10 wt %. [ABSTRACT FROM AUTHOR]