Morphology of the polar twin structure in Czochralski grown alpha -SrB sub(4)O sub(7) crystals

The arrangement of a polar twin structure in Czochralski grown alpha -SrB sub(4)O sub(7) crystals has been investigated. The transversal twin boundaries are stretched along [1 0 1] and [1 0 0] directions. The lateral twin boundaries are parallel to (0 1 0) plane. The twin structures have an extension up to centimeter size in all directions. Supposedly, they originate from polysynthetic polar microtwins revealed to form in (1 0 1) and (1 0 1) growth pyramids. The dimensions, planarity and thickness stability of each individual twin are favorable for organizing quasi-phase matching conditions for nonlinear optical doubling of high-aperture beams.