High Temperature form BBO ( alpha-BBO) is a negative uniaxial crystal. It has large birefringence over the broad transparent range from 189 nm to 3500 nm. The physical, chemical, thermal and optical properties of alpha-BBO crystal are similar to those of beta-BBO. There is no second order nonlinear effect in alpha-BBO crystal due to the centric symmetry in its crystal structure and thus it has no use for NLO processes. Instead, alpha-BBO is widely used for fabrication of polarizers, phase retarders, birefringent plates, especially those for  UV and high power operations.