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LBO(LiB3O5) is another excellent nonlinear crystal of Borate-family following BBO crystal. LBO has a broad transmission range from DUV to mid infrared, higher damage threshold than any other NLO crystals and is capable of noncritical phase matching (NCPM) in the near IR region, making it the material of choice for high power, high efficiency second harmonic generation (SHG) and optical parametric processes (OPO/OPA). LBO crystals are offen mounted in temperature controlled ovens either for NCPM SHG or tunable OPO/OPA applications.
- Broad transparency range from 160-2600nm
- High optical homogeneity ( 1.0E-6/cm) and being free of inclusion;
- Medium effective SHG coefficient(about three times that of KDP)
- High damage threshold
- Wide acceptance angle and small walk-off
- Type I and type II non-critical phase matching (NCPM)
- Spectral NCPM near 1300nm
LBO is phase matchable for the SHG and THG of Nd:YAG and Nd:YLF lasers, using either type I or type II interaction. For the SHG at room temperature, type I phase matching LBO can be reached and has the maximum effective SHG coefficient in the principal XY and XZ planes in a wide wavelength range from 551nm to about 2600nm. LBO optimum type II phase matching falls in principal YZ and XZ planes.
SHG conversion efficiencies of more than 70% for pulse and 30% for cw Nd:YAG lasers, and THG conversion efficiency over 60% for pulse Nd:YAG laser have been observed by using LBO crystal.
Properties of type I NCPM SHG@1064nm:
NCPM Temperature: 148°C
Acceptance Angle: 52 mrad-cm1/2
Walk-off Angle: 0
Temperature Bandwidth: 4°C-cm
Effective SHG Coefficient: 2.69 d36(KDP)
As shown above, Non-Critical Phase-Matching (NCPM) of LBO is featured by no walk-off, very wide acceptance angle and maximum effective coefficient. It promotes LBO to work in its optimal condition. LBO SHG conversion efficiencies of more than 70% for pulse and 30% for cw Nd:YAG lasers have been obtained, with good output stability and beam quality.
Oven & Temperature Controller for LBO NCPM, OPO/OPA applications are available from OptoCity.
LBO is an excellent NLO crystal for OPOs and OPAs with a widely tunable wavelength range and high powers. LBO OPO and OPA that are pumped by the SHG and THG of Nd:YAG laser and XeCl excimer laser at 308nm have been reported. The unique properties of type I and type II phase matching as well as the NCPM leave a big room in the research and applications of LBO’s OPO and OPA.
Not only the ordinary non-critical phase matching (NCPM) for angular variation but also the noncritical phase matching for spectral variation (SNCPM) can be achieved in the LBO crystal. The phase matching retracing positions are 1.31µm with theta=86.4°, Fi=0° for Type I and 1.30µm with theta=4.8°, Fi=0° for Type II. The phase matching at these positions possess very large spectral acceptances. The calculated spectral acceptances at 1.31um and 1.30um are 57nm-cm-1/2 and 74nm-cm-1/2 respectively, which are much larger than that of other NLO crystals. These spectral characteristics are very suitable for doubling broadband coherent radiations near 1.3µm, such as those from some diode lasers, and some OPA/OPO output without linewidth-narrowing components.
Crystal Structure:Orthorhombic Space group Pna21, Point group mm2
Lattice Parameter: a=8.4473Å, b=7.3788Å , c=5.1395Å , Z=2
Melting Point : About 834 °C
Mohs Hardness: 6
Density: 2.47 g/cm³
Thermal Conductivity: 3.5W/m/K
Thermal Expansion Coefficient:
α(x)=10.8x10E-5/K, α(y)= -8.8x10E-5/K, α(z)=3.4x10E-5/K
SHG Phase Matchable, Type I: 551 ~ 2600nm, Type II: 790-2150nm
Therm-optic Coefficient: dnx/dT=-9.3x10E-6/°C
Absorption Coefficient: <0.1%/cm @1064nm, <0.3%/cm @532nm
NLO Coefficients:d31=1.05pm/V d32= -0.98pm/V d33=0.05pm/V
Sellmeier Equations (λ in μm)
Dimension Tolerance: +0/-0.1mm(WxH), +/- 0.1 mm thickness
Surface Quality: 10-5 Scratch-dig
Flatness: <λ/8 @633nm
Clear Aperture: Central 90% of Diameter
Parallelism: <20 arc seconds
Perpendicular: <20 arc minutes
Orientation Angle: +/-0.25deg.
Damage Threshold: 18.9GW/cm2@1064nm 1 ns (polished only)
Coating:Dual Band AR coating: R<0.2%@ω & R<0.5%@2ω
Coating Damage Threshold: 5GW/cm2@1064nm 1 ns
Broad Band AR-coating is also available for LBO crystal
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