Beta barium borate

From Wikipedia, the free encyclopedia

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. 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 possesses centric symmetry and thus does not have the same harmonic generation capabilities as the β phase.

1 Advantages
2 Properties
3 References

[edit] Advantages

Broad phase-matchable range from 409.6–3500 nm.
Wide transmission region from 190–3500 nm.
Large effective second-harmonic generation (SHG) coefficient: approximately 6 times greater than that of KDP.
High damage threshold of 10 GW/cm² for 100 ps pulse-width at 1064 nm.
High optical homogeneity with Δn=10^-6/cm.
Wide temperature-bandwidth of about 55°C.

[edit] Properties

[edit] Physical

Crystal structure: Trigonal, space group R3c
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
Absorption coefficient at 1064nm: <0.1%/cm³
Hygroscopic susceptibility: low
Resistivity: >1011 Ω·cm

[edit] Optical

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: $n_o=1.75, \quad n_e=1.61$
Optical homogeneity Dn: $10^{-6}\ \mathrm{cm}^{-1}$
Transparency range: 189–3500 nm
Phase matchable range (SHG): 189–1750 nm
Effective nonlinear coefficient: 4–6 × KDP
Acceptance angle: 0.2–1 mrad·cm
Walk-off angle, from SHG–5HG of Nd:YAG laser: 3.2°–5.5°
Thermo-optic coefficients:

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

[edit] Sellmeier equations

$n^2_o(\lambda) = 2.7359+0.01878/(\lambda^2 - 0.01822)-0.01354 \times \lambda^2$ in micrometers
$n^2_e(\lambda) = 2.3753+0.01224/(\lambda^2-0.01667)-0.01516 \times \lambda^2$ in micrometers