LBO (Lithium Triborate)
Lithium Tri-borate (LBO) is one of the most useful nonlinear optical material not just for its relatively large conversion coefficient - 3x that of KDP, but also for its excellent physical properties.
LBO crystal has broad optical transparency range from 160 to 2600nm. It excels in high power SHG with minimal thermal lensing as compared to KTP. Its large acceptance angle paired with small walk-off angle which reduces the beam quality requirement for source lasers. LBO also allows temperature controllable type I non-critical phase-matching(NCPM) for 1000 – 1300nm and type II NCPM for 800 to 1100nm at room temperature. With a high optical homogeneity (?n ~10-6), the material is grown virtually inclusion free. With a damage threshold of up to 45 GW/cm2 at 1064nm, it is again the material of choice for high power applications.
LBO is widely used for SHG and THG of Nd:YAG, Nd:YLF, Nd:YVO4 and ultra-fast Ti:sapphire lasers. OPOs(Optical Parametric Oscillators) and OPAs(Optical Parametric Amplifier).
Crystal Structure and Physical Properties
| Chemical Formula | LiB3O5 |
| Crystal Structure | Orthorhombic, mm2 |
| Cell Parameters | a = 8.4473, b = 7.3788Å, c = 5.1395Å, Z = 2 |
| Melting point | 834°C |
| Optical homogeneity | d n ~ 10-6/cm |
| Mohs hardness | 6 |
| Density | 2.47 g/cm3 |
| Absorption coefficient | < 0.1%/cm (at 1064nm and 532nm) |
| Specific heat | 1.91J/cm3xK |
| Hygroscopic susceptibility | low |
| Thermal expansion coefficients | a, 4 x 10-6/K; c, 36 x 10-6/K |
| Thermal conductivity | ^ c, 1.2 W/m/K; //c, 1.6 W/m/K |
Linear Optical Properties
| Transparency range | 160-2600nm |
| Refractive indices: at 1064nm at 532nm at 355nm |
nx = 1.5656, ny = 1.5905, nz = 1.6055 ne = 1.5785, no = 1.6065, nz = 1.6212 ne = 1.5971, no = 1.6275, nz = 1.6430 |
| Therm-optic coefficients | dno/dT = -9.3 x 10-6/°C dne/dT = -16.6 x 10-6/°C |
| Sellmeier Equations (l in mm) | |
| no2 (l) = 2.7359 - 0.01354l2+ 0.01878/(l2-0.01822) ne2(l) = 2.3753 - 0.01516l2+ 0.01224/(l2-0.01667) |
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Nonlinear Optical Properties
| Phase-matchable output wavelength | 554 - 2660nm (type I), 790 – 2150nm (type II) |
| NLO coefficients | d33 = 0.06; d32 = 1.2; d22 = 1.1 |
| Walk-off Angles(@ 1064nm) | 0.4° (Type I SHG), 0.3° (Type II SHG) |
| Acceptance Angles(@1064nm) for SHG Type I | 9.6(mrad-cm) CPM at 25°C 248(mrad-cm) NCPM at 150°C |
| Electro-optic coefficients | g 11 = 2.7 pm/V, g 22, g31 < 0.1g11 |
| Conversion Efficiency | >90% (1064 -> 532nm) Type I SHG |
| Damage threshold at 1064nm at 532nm at 355nm |
45 GW/cm2 (1 ns); 10 GW/cm2 (1.3 ns) 26 GW/cm2 (1 ns); 7 GW/cm2 (250 ps) 22 GW/cm2 |
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Datasheet (PDF)