Flexoelectric Fracture-Ratchet Effect in Ferroelectrics

The propagation front of a crack generates large strain gradients and it is therefore a strong source of gradient-induced polarization (flexoelectricity). Herein, we demonstrate that, in piezoelectric materials, a consequence of flexoelectricity is that crack propagation is helped or hindered depending on whether it is parallel or antiparallel to the piezoelectric polar axis. The discovery of crack propagation asymmetry proves that fracture physics cannot be assumed to be symmetric in polar materials, and indicates that flexoelectricity should be incorporated in any realistic model.

Quasi-phase matched second harmonic generation in periodically poled Rb-doped KTiOPO4 ridge waveguide

A 10.8 µm wide ridge waveguide was fabricated by diamond-blade dicing in an ion-exchanged periodically poled Rb-doped KTiOPO₄ sample. The waveguide was used to generate blue second harmonic light at 468.8 nm in the TM₀₀ mode through first order Type I quasi-phase matching, exploiting the large d₃₃ coefficient of the crystal. It was evaluated using a cw Ti:Sapphire laser, and 6.7 µW of blue light was generated with 5.8 mW of fundamental radiation at 933.8 nm coupled through the waveguide. The results presented here pave the way for efficient nonlinear processes in a waveguide format.

Contact poling of Rb:KTiOPO(4) using a micro-structured silicon electrode

A contact poling technique for domain engineering of ferroelectrics using a micro-structured silicon electrode is demonstrated on Rb:KTiOPO₄. High quality QPM gratings were reproducibly fabricated. The silicon electrode is reusable and the technique potentially suitable when complex structures with sub-μm features are to be domain engineered, which otherwise is incompatible with conventional photolithography. A non-negligible domain broadening was seen and attributed to a low nucleation rate using this type of electrode. However, under the appropriate poling conditions, this could be exploited to obtain a QPM grating with a short pitch (2 μm), equal to half of the electrode period.