β-Barium Borate (BBO) Crystal
BBO crystal (β-BaB₂O₄) is a trigonal non-centrosymmetric nonlinear optical crystal. It is well‑known for generating the 2nd to 5th harmonics of Nd:YAG laser with high efficiency: up to 70% for SHG (532 nm), 60% for THG (355 nm), 50% for FHG (266 nm), and a record output of 200 mW at 213 nm (FFHG). Its outstanding performance comes from a wide transparency range (189–3500 nm), large nonlinear coefficient (d₁₁ = 2.6 pm/V at 1064 nm→532 nm), low refractive index, and non‑hygroscopic property, making it essential for UV lithography, laser micromachining, and medical optics.
