Beta barium borate

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 thepositions 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.

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

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

Optical properties

*Refractive index, 1064 nm: $n\_o=1.65,\; quad\; n\_e=1.54$
*Refractive index, 532 nm: $n\_o=1.67,\; quad\; n\_e=1.55$
*Refractive index, 266 nm: $n\_o=1.75,\; quad\; n\_e=1.61$
*Transparency range (> 0.5 cm^-1): 198–2600 nm
*Thermo-optic coefficients:cite journal| author=D. N. Nikogosyan | title=Beta Barium Borate (BBO)| journal=Applied Physics A| volume=52 | pages=359--368] :*$frac\{partial\; n\_o\}\{partial\; T\}=\; -9.3\; imes\; 10^\{-6\}\; /\; mathrm\{^circ\; C\}$:*$frac\{partial\; n\_e\}\{partial\; T\}\; =\; -16.6\; imes\; 10^\{-6\}\; /\; mathrm\{^circ\; C\}$

*Nonlinear optical coefficients: cite book| author= V.G. Dmitriev, G. G. Gurzadyan, and D. N. Nikogosyan | title=Handbook of Nonlinear Optical Crystals, 3rd edition| publisher=Springer | date=1999| isbn=0342-4111] :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.

ellmeier equations (for λ in microns)

*$n^2\_o(lambda)$ = 2.7359+0.01878/(λ² - 0.01822)-0.01354 λ² cite journal| author=Kato, K. |journal = IEEE Journal of Quantum Electronics | volume=22| number = 7 | date=1986|title= Second-harmonic generation to 2048 Å in β-BaB₂O₄ | pages= 1013--1014|doi= 10.1109/JQE.1986.1073097]
*$n^2\_e(lambda)$ = 2.3753+0.01224/(λ²-0.01667)-0.01516 λ²

References

External links

*cite web |url=http://www.photox.co.uk/bbo.htm |title=BBO Crystal β-Barium Borate |accessdate=2006-10-23 |work=Photox Optical Systems website