Beta barium borate(BBO) crystal is one of the best non-linear optical crystals with high effective nonlinear optical coefficient, high damage threshold, wide phase matching range and high deep UV transmittance.
BBO is a negative uniaxial crystal, and its o-ray refractive index (no) is larger than the e-ray (ne) refractive index.
These features of nonlinear BBO crystal includes wide transparency and phase matching ranges, large non-linear coefficient, high damage threshold and excellent optical homogeneity.