Effect of proton exchange on the nonlinear optical properties of LiNbO3 and LiTaO3

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Abstract
The effect of proton exchange carried out using benzoic and pyrophosphoric acid on the nonlinear optical coefficient (d) of LiNbO3 and LiTaO3 was studied using a second‐harmonic generation reflectance technique. Significant degradation in the d coefficient of LiNbO3 and LiTaO3 was observed as a result of proton exchange with either benzoic or pyrophosphoric acid under the conditions studied. Some recovery only in the short time proton‐exchanged sample (0.5 h at 180 °C) of LiNbO3 was observed under thermal annealing at 350 °C for 1 h. Results of in situ measurement of second‐harmonic signal recovery under thermal annealing are reported. Results are also presented on theoretical and experimental variations of second‐harmonic generation intensity with an incident polarization angle.