BBO (Beta-Barium Borate or β-BaB2O4)is an outstanding nonlinear optical crystal which has the obvious and unique advantages on frequency conversions of high peak power laser radiation from UV to VIS. BBO is grown with the flux method. It is a negative uniaxial crystal, with ordinary refractive-index (no) larger than extraordinary refractive-index (ne).  Both type I and type II phase-matching can be reached by angle-tuning.