Beta barium borate

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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.

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[edit] Advantages of BBO

Broad phase-matchable range from 409.6nm - 3500nm.

Wide transmission region from 190nm - 3500nm.

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 1064nm.

High optical homogeneity with delta n=10-6/cm.

Wide temperature-bandwidth of about 55°C.

[edit] Properties

[edit] Physical

Crystal structure: Trigonal, space group R3c

Lattice parameters: a=b=1.253nm, c=1.272nm, Z=6

Melting point: 1095±5°C

Phase transition temperature: 925±5°C

Mohs hardness: 4.5

Density: 3.85 g/cm3

Absorption coefficient @ 1064nm: <0.1%/cm3

Hygroscopic susceptibility: low

Resistivity: >1011 ohm-cm


[edit] Optical

Refractive index, 1064nm: n_o=1.65, \quad n_e=1.54

Refractive index, 532nm: n_o=1.67, \quad n_e=1.55

Refractive index, 266nm: n_o=1.75, \quad n_e=1.61

Optical homogeneity Dn: 10 − 6cm − 1

Transparency range: 189-3500 nm

Phase matchable range (SHG): 189-1750 nm

Effective nonlinear coefficient: 4-6 x 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} / {}^\circ C

\frac{\partial n_e}{\partial T} = -16.6 \times 10^{-6} / {}^\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

[edit] References

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