β-BBO Crystal—a widely used nonlinear crystal for frequency conversion in the ultraviolet, visible and near-infrared

BBO Crystal is a one of the most important nonlinear optical crystals, beta-barium borate (β-BaB2O4，β-BBO) combines many outstanding features such as its high nonlinear optical coefficients, low group-velocity dispersion, broad transparency range (189–3500 nm) and high damage threshold. This unique combination ensures β-BBO crystal a promising candidate for a wide range of nonlinear optical applications such as frequency converters and optical parametric oscillators. In the realm of quantum optics, β-BBO crystal can be used to generate entangled photon pairs and ten-photon entanglement.

BBO nonlinear crystal is a negative uniaxial crystal, which provides phase matching for various second-order interactions almost over its entire transparency range (from 185 nm to 3.3 µm, as deduced from the transmittance measurements using crystal samples of several mm thickness), making it a widely used crystal for nonlinear frequency conversion in the ultraviolet, visible and near-infrared. In that regard, BBO crystal is the most important nonlinear crystal for near infrared optical parametric chirped pulse amplifiers, which currently deliver few optical cycle pulses with high average and ultrahigh peak powers.