Enhancement of second harmonic generation signal in thermally poled glass ceramic with NaNbO{sub 3} nanocrystals

Glass ceramic composites were prepared by bulk crystallization of NaNbO{sub 3} in sodium niobium borate glasses. A homogeneous bulk crystallization of the NaNbO{sub 3} phase takes place during heat treatments that produces visible-near infrared transparent materials with {approx}30 nm NaNbO{sub 3} nanocrystallites. Upon thermal poling, a strong Na{sup +} depleted nonlinear optical thin layer is observed at the anode side that should induce a large internal static electric field. In addition, the {chi}{sup (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 {chi}{sup (2)} process connected with the occurrence of a spontaneous ferroelectric polarization or an increase of the {chi}{sup (3)} response of the nanocrystallites that enhances the electric field induced second harmonic generation process.