Beta barium borate (β-barium borate, BBO or β-BaB₂O₄) is a crystal frequently used for frequency mixing and other nonlinear optics applications. It has a wide transmission range, from approximately 200 nanometres to beyond 3 micrometres, and is used particularly for its transparency in the deep ultraviolet.

BBO has a trigonal crystal system, belongs to crystallographic point group 3m, and belongs to the crystallographic space group R3c. BBO has strong negative uniaxial birefringence and can be phase-matched for type I (ooe) second harmonic generation from 409.6–3500 nm. The temperature sensitivity of the indices of refraction is low, leading to an unusually large (55 °C) temperature phase-matching bandwidth. The crystal is mildly hygroscopic.

β-Barium borate differs from α-barium borate in the positions of the barium ions within the crystal. Both phases are birefringent, however the α phase, which exists above 925 °C, possesses centric symmetry and thus does not have the same nonlinear properties as the β phase.^[1]

BBO is a common material used to split photons to produce the phenomenon of quantum entanglement.

Contents 1 Physical properties 2 Optical properties 2.1 Sellmeier equations (for λ in micrometres) 3 References 4 External links

[edit] Physical properties

• Lattice parameters: a=b=1.253 nm, c=1.272 nm, Z=6
• Melting point: 1095±5 °C
• Phase transition temperature: 925±5 °C
• Mohs hardness: 4.5
• Density: 3.85 g/cm³

[edit] Optical properties

• Refractive index, 1064 nm:
• Refractive index, 532 nm:
• Refractive index, 266 nm:
• Transparency range (> 0.5 cm^-1): 198–2600 nm^[1]
• Thermo-optic coefficients:^[1]

• 
• 

• Nonlinear optical coefficients: ^[2]

d₂₂ = 2.3 pV / m.

d₃₁ = -0.16 pV / m.

• High damage threshold of 10 GW/cm² for 100 ps pulse-width at 1064 nm.

[edit] Sellmeier equations (for λ in micrometres)

• = 2.7359+0.01878/(λ² - 0.01822)-0.01354 λ^{2 [3]}
• = 2.3753+0.01224/(λ²-0.01667)-0.01516 λ^{2 [3]}

[edit] References

1. ^ ^{a b c} D. N. Nikogosyan. "Beta Barium Borate (BBO)". Applied Physics A 52: 359--368. 
2. ^ V.G. Dmitriev, G. G. Gurzadyan, and D. N. Nikogosyan (1999). Handbook of Nonlinear Optical Crystals, 3rd edition. Springer. ISBN 0342-4111. 
3. ^ ^{a b} Kato, K. (1986). "Second-harmonic generation to 2048 Å in β-BaB₂O₄". IEEE Journal of Quantum Electronics 22 (7): 1013--1014. doi:10.1109/JQE.1986.1073097. 

[edit] External links

• "BBO Crystal β-Barium Borate". Photox Optical Systems website. http://www.photox.co.uk/bbo.htm. Retrieved 2006-10-23.