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)

 

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)