Barium Borate (a-BBO) Crystal

High Temperature form BBO (a-BaB2O4) is a negative uniaxial crystal. It has large birefringence over the broad transparent range from 189 nm to 3500 nm. Recently, CASIX has succeeded in growing this crystal into large size. The physical, chemical, thermal and optical properties of a-BBO crystal are similar to those of b-BBO. However, the nonlinear optical properties of a-BBO crystal is vanished due to the centric symmetry with its crystal structure. It is not recommended to use for NLO processes.

a-BBO is an excellent crystal to replace Calcite, TiO2, and LiNbO3, etc. in Glan-Taylor and Glan-Thompson polarizers as well as walk-off beam splitters, especially for high power and UV polarizer, due to its unique UV transparency, good mechanical properties and high damage threshold. CASIX manufactures and supplies Glan-Laser, Glan-Taylor, Glan-Thompson Polarizers and other beam displacers from high quality a-BBO crystals to replace Calcite in many applications, especially in UV and high power operations.

1. Basic Properties of a-BBO


Transparency Range:
189 - 3500 nm, See Transparency Curve

alfa-bboCurve.JPG (15167 bytes)

Transparency Curve of a-BBO

Density: 3.85 g/cm3
Therm-Optic Coefficients:
dno/dT = -9.3 x 10-6/oC
dne/dT = -16.6 x 10-6/oC
Damage Threshold
at 1064 nm           1GW/cm2
at 355 nm            500 MW/cm2
Optical Homogeneity:Dn » 10-6/cm
Mohs Hardness: 4.5
Hygroscopic Susceptibility:Low
Thermal Expansion Coefficients
(in the range of 25oC – 900oC)
aa= 4 x 10-6/K
ac= 36 x 10-6/K

Linear Absorption Coefficients: a <0.005 cm-1 from 300 nm to 2300 nm

Refractive Indices, Birefringence (Dn = ne - no) and Walk-off Angle at 45o (r):
at 1.0642 mm ne= 1.5379, no = 1.6579      Dn =-0.073282 r =-4.9532°
at 0.5321 mm ne = 1.5534, no = 1.6776      Dn =-0.075491  r =-5.0407°
at 0.2660 mm ne = 1.6114, no = 1.7617 Dn=-0.089805 r =-5.6926°

2. Specifications of a-BBO

Surface Quality

20/10 Scratch and Dig

Beam Deviation

<3 arc min.

Optical Axis Orientation

+/-0.5°

Flatness

l/4 @ 632.8 nm

Transmission Wavefront Distortion

<l /2 @632.8 nm

AR-coating

R<0.5%


3. Applications of a-BBO

Please refer to Polarizer for the applications of a-BBO.