High-contrast coercive field engineering for periodic poling of RbKTiOPO₄ with Ba²⁺/K⁺ ion-exchange

We investigate a new method of coercive field engineering for periodic poling of RbKTiOPO₄ (RKTP). By ion exchanging RKTP in a molten salt containing 7 mol% Ba(NO₃)₂ and 93 mol% KNO₃ we achieve more than an order of magnitude difference in polarization switching time between the exchanged and non-exchanged regions. This method is used to fabricate periodic gratings of 2.92 µm in 1 mm thick bulk RKTP for second harmonic generation at 779 nm with a normalized conversion efficiency of 2%/Wcm. We show that the poled domain structures are stable at 300 °C, and that there is no bulk refractive index modification associated with the periodic ion exchange.