Enhancement of second harmonic generation signal in thermally poled glass ceramic with NaNbO_3 nanocrystals

摘要

Glass ceramic composites were prepared by bulk crystallization of NaNbO_3 in sodium niobium borate glasses. A homogeneous bulk crystallization of the NaNbO_3 phase takes place during heat treatments that produces visible-near infrared transparent materials with ～30 nm NaNbO_3 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 1.9 pm/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.