α-BBO (α-BaB2O4) is a negative uniaxial crystal which has large birefringence over a broad transparent range of 190nm to 3500nm. α-BBO is an excellent crystal, suitable for the manufacture of polarizer, polarization beam displacer, time delay compensator plate and other birefringent device, especially for UV and high power applications. The physical, chemical, thermal and optical properties of α-BBO crystal are similar to those of β-BBO. However, the nonlinear optical properties of α-BBO crystal are nonexistent due to the centric symmetry with its crystal structure. α-BBO crystal is not recommended for NLO processes.