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 to 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]

The nonlinear nature of BBO allows for the production of pairs of photons via spontaneous parametric down-conversion. This is an important resource for experimental quantum information, particularly as a method of producing entangled photons.^[2]

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

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^[1]
Thermo-optic coefficients:^[1]

$\frac{\partial n_o}{\partial T}= -9.3 \times 10^{-6} / \mathrm{^\circ C}$
$\frac{\partial n_e}{\partial T} = -16.6 \times 10^{-6} / \mathrm{^\circ C}$

Nonlinear optical coefficients:^[3]

d₂₂ = 2.3 pm/V

d₃₁ = -0.16 pm/V

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

Sellmeier equations (for λ in micrometres)

$n^2_o(\lambda)$ = 2.7359+0.01878/(λ² - 0.01822)-0.01354 λ² ^[4]
$n^2_e(\lambda)$ = 2.3753+0.01224/(λ²-0.01667)-0.01516 λ² ^[4]

References

^ ^a ^b ^c D. N. Nikogosyan. "Beta Barium Borate (BBO)". Applied Physics A 52: 359–368.
^ Gerry, C; Knight, P (2005). Introductory quantum mechanics. Campbridge University Press. ISBN 9780521527354. http://books.google.com/?id=CgByyoBJJwgC&printsec=frontcover&dq=gerry+and+Knight#v=onepage&q&f=false. , [1]
^ V.G. Dmitriev, G. G. Gurzadyan, and D. N. Nikogosyan (1999). Handbook of Nonlinear Optical Crystals, 3rd edition. Springer. ISBN 0342-4111.
^ ^a ^b Kato, K. (1986). "Second-harmonic generation to 2048 Å in β-BaB₂O₄". IEEE Journal of Quantum Electronics 22 (7): 1013–1014. Bibcode 1986IJQE...22.1013K. doi:10.1109/JQE.1986.1073097.

External links

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