UV laser-induced poling inhibited domain building blocks for photonic and nonlinear optical microstructures

Summary form only given. UV laser induced poling inhibition (PI) is a method for domain engineering in ferroelectric lithium niobate crystals. This method is capable of producing localised ferroelectric domains whose shape and orientation is defined by a UV laser pre-irradiated pattern. Poling inhibition is observed at the locations of the +z face of the crystal that have been exposed to UV laser radiation (244 nm-305 nm) prior to uniform domain inversion by electric field poling at room temperature [1].Poling inhibition is attributed to lithium migration under the influence of steep temperature gradients which form due to the strong absorption of UV radiation within a small crystal volume thus, raising the temperature close to the melting point which is ~ 1250°C. Lithium ions migrate away from the hot crystal volume resulting in local variation of lithium concentration, which produces a corresponding local variation of the coercive field [2]. The coercive field variation, which reflects the lithium concentration distribution is responsible for the spatially selective domain inversion when applying a uniform electric field. UV laser induced PI has been demonstrated in both congruent and MgO doped crystals. PI normally requires tight focussing of the UV laser. The width of the resulting PI domains corresponds to the temperature distribution which is induced by the irradiating beam. Consequently, only small (a few μm) size domain widths have been achieved so far [3]. Here we demonstrate that partial overlap of UV-irradiated tracks can produce larger PI domains, which consist of merged individual PI domains as defined by individual UV laser tracks, thus removing the restriction, which was imposed by the limited width of the UV irradiated beam. We show that individual pole inhibited domain tracks can be stitched together to produce larger and more complex structures with precise specifications. The result of such a domain-stitching process is demonstrat- d in the SEM microscopy images of figure 1 where a set of three ring and three disc structures is shown. These structures are composed of concentric ring shaped domains, which are combined to produce rings of varying width and discs of varying diameter. The composite domain structure has been made visible by wet etching in HF acid solution Measurement of the PI domain depth as a function of the overlapping factor between adjacent UV irradiated track revealed that overlapped irradiation does not influence the PI depth. The depth of the composite PI domains was measured from the SEM images of wedge polished and chemically etched samples.The ability to combine individual PI domains to construct larger and more complex structures increases dramatically the utility of this method for the fabrication of arbitrary surface microstructures as well as periodic and aperiodic nonlinear optical and acoustic lattices.