Fabrication of 90° domain structures in KNbO3 single crystals

New domain (90degrees domain) structure in the KNbO3 single crystal could be fabricated by applying electric field at room temperature. The coercive electric field of 90degrees domain is very low (140 V/mm) compared with that of 180degrees domain (250 V/mm). A very sharp boundary was observed across the whole sample thickness (2 mm). Fabricated 90degrees domain structures were also confirmed by the (101) surface profile measurement using the optical interferrometer and two peaks of the 404 X-ray diffraction analysis. We also demonstrated the fabrication of periodically 90degrees domain structures with 200 mum period without generating unwanted domain structures. As 90degrees domain structure feels the difference of the refractive index, new applications other than 180degrees domain will be possible.