Lithium Triborate (LiB3O5 , LBO)
Introduction
Lithium Triborate (LiB3O5 or LBO) is an excellent nonlinear optical crystal. Now LaserMa provides high quality LBO crystals for many applications.
LaserMa's LBO is featured by
• broad transparency range from 160nm to 2600nm (see Figure 1);
• high optical homogeneity (dn»106/cm) and being free of inclusion;
• relatively large effective SHG coefficient (about three times that of KDP);
• high damage threshold;
• wide acceptance angle and small walkoff;
• type I and type II noncritical phase matching (NCPM) in a wide wavelength range;
• spectral NCPM near 1300nm.
LaserMa offers
• strict quality control;
• large crystal size up to 30x30x30mm3 and maximum length of 60mm;
• ARcoating, mounts and repolishing services;
• a large quantity of crystals in stock;
• fast delivery(10 days for polished only, 15 days for ARcoated).
Table 1. Chemical and Structural properties
Crystal Structure 
Orthorhombic, Space group Pna2_{1}, Point group mm2 
Lattice Parameter 
a=8.4473Å, b=7.3788Å , c=5.1395Å , Z=2 
Melting Point 
About 834℃ 
Mohs Hardness 
6 
Density 
2.47 g/cm^{3} 
Thermal Conductivity 
3.5W/m/K 
Thermal Expansion Coefficient 
a_{x}=10.8x10^{5}/K, a_{y}= 8.8x10^{5}/K, a_{z}=3.4x10^{5}/K 
Table 2. Optical and Nonlinear Optical Properties
Transparency Range 
1602600nm 
SHG Phase Matchable Range 
551 ~ 2600nm (Type I) 7902150nm (Type II) 
Thermoptic Coefficient
(°C, λ in μm) 
dnx/dT=9.3X10^{6} dny/dT=13.6X10^{6} dnz/dT=(6.32.1λ)X10^{6} 
Absorption Coefficient 
<0.1%/cm at 1064nm <0.3%/cm at 532nm 
Angle Acceptance 
6.54mradcm (φ, Type I,1064 SHG) 15.27mradcm (q, Type II,1064 SHG) 
Temperature Acceptance 
4.7°Ccm (Type I, 1064 SHG) 7.5°Ccm (Type II,1064 SHG) 
Spectral Acceptance 
1.0nmcm (Type I, 1064 SHG) 1.3nmcm (Type II,1064 SHG) 
Walkoff Angle 
0.60° (Type I 1064 SHG) 0.12° (Type II 1064 SHG) 
NLO Coefficients 
d_{eff}(I)=d_{32}cosΦ (Type I in XY plane) d_{eff}(I)=d_{31}cos^{2}θ+d_{32}sin^{2}θ (Type I in XZ plane) d_{eff}(II)=d_{31}cosθ (Type II in YZ plane) d_{eff}(II)=d_{31}cos^{2}θ+d_{32}sin^{2}θ (Type II in XZ plane) 
Nonvanished NLO susceptibilities 
d_{31}=1.05 ± 0.09 pm/V d_{32}= 0.98 ± 0.09 pm/V d_{33}=0.05 ± 0.006 pm/V 
Sellmeier Equations(λ in μm) 
n_{x}^{2}=2.454140+0.011249/(λ^{2}0.011350)0.014591λ^{2}6.60x10^{5}λ^{4}n_{y}^{2}=2.539070+0.012711/(λ^{2}0.012523)0.018540λ^{2}+2.0x10^{4}λ^{4}n_{z}^{2}=2.586179+0.013099/(λ^{2}0.011893)0.017968λ^{2}2.26x10^{4}λ^{4} 

Figure 1. Transparency curve of LBO 
SHG and THG at Room Temperature

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 can be reached and has the maximum effective SHG coefficient in the principal XY and XZ planes (see Fig. 2) in a wide wavelength range from 551nm to about 2600nm. The optimum type II phase matching falls in principal YZ and XZ planes(see Fig 2). 
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 LASERMA’s LBO crystals.
Applications
* More than 480mW output at 395nm is generated by frequency doubling a 2W modelocked Ti:Sapphire laser (<2ps, 82MHz). The wavelength range of 700900nm is covered by a 5x3x8mm^{3} LBO crystal. * Over 80W green output is obtained by SHG of a Qswitched Nd:YAG laser in a type II 18mm long LBO crystal. * The frequency doubling of a diode pumped Nd:YLF laser (>500µJ @ 1047nm, <7ns, 010KHz) reaches over 40% conversion efficiency in a 9mm long LBO crystal. * The VUV output at 187.7 nm is obtained by sumfrequency generation. * 2mJ/pulse diffractionlimited beam at 355nm is obtained by intracavity frequency tripling a Qswitched Nd:YAG laser.
NonCritical PhaseMatching
Table 3. Properties of type I NCPM SHG at 1064nm 
NCPM Temperature Acceptance Angle Walkoff Angle Temperature Bandwidth Effective SHG Coefficient 
148°C 52 mradcm^{1/2}0 4°Ccm 2.69 d_{36}(KDP) 
AS shown in table 3, NonCritical PhaseMatching (NCPM) of LBO is featured by no walkoff, very wide acceptance angle and maximum effective coefficient. It promotes LBO to work in its optimal condition. 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.
As shown in Fig.3, type I and type II noncritical phasematching can be reached along xaxis and zaxis at room temperature, respectively.(LASERMA develops an assembly of oven and temperature controller for NCPM applications. Please refer to Page 20 for more technical data.)

Figure 3.NCPM temperature tuning curves of LBO 
Applications
* Over 11W of average power at 532nm was obtained by extracavity SHG of a 25W Antares modelocked Nd:YAG laser (76MHz, 80ps).
* 20W green output was generated by frequency doubling a medical, multimode Qswitched Nd:YAG laser. Much higher green output is expected with higher input.
LBO’s OPO and OPA
LBO is an excellent NLO crystal for OPOs and OPAs with a widely tunable wavelength range and high powers. These 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. Fig.4 shows the calculated type I OPO tuning curves of LBO pumped by the SHG, THG and 4HG of Nd:YAG laser in XY plane at the room temperature. And Fig. 5 illustrates type II OPO tuning curves of LBO pumped by the SHG and THG of Nd:YAG laser in XZ plane.


Figure 4. Type I OPO tuning curves of LBO 
Figure 5. Type II OPO tuning curves of LBO 
Applications
* A quite high overall conversion efficiency and 5401030nm tunable wavelength range were obtained with OPO pumped at 355nm. * Type I OPA pumped at 355nm with the pumptosignal energy conversion efficiency of 30% has been reported. * Type II NCPM OPO pumped by a XeCl excimer laser at 308nm has achieved 16.5% conversion efficiency, and moderate tunable wavelength ranges can be obtained with different pumping sources and temperature tuning. * By using the NCPM technique, type I OPA pumped by the SHG of a Nd:YAG laser at 532nm was also observed to cover a wide tunable range from 750nm to 1800nm by temperature tuning from 106.5°C to 148.5°C. * By using type II NCPM LBO as an optical parametric generator (OPG) and type I critical phasematched BBO as an OPA, a narrow linewidth (0.15nm) and high pumptosignal energy conversion efficiency (32.7%) were obtained when it is pumped by a 4.8mJ, 30ps laser at 354.7nm. Wavelength tuning range from 482.6nm to 415.9nm was covered by increasing the temperature of LBO or rotating BBO.
LBO’s Spectral NCPM
Not only the ordinary noncritical phase matching (NCPM) for angular variation but also the noncritical phase matching for spectral variation (SNCPM) can be achieved in the LBO crystal. As shown in Fig.2, the phase matching retracing positions are λ_{1}^{}=1.31μm with θ =86.4°, φ=0° for Type I and λ_{2}^{}=1.30μm with θ=4.8°, φ=0° for Type II. The phase matching at these positions possess very large spectral acceptances Δλ. The calculated Δλ at λ_{1}^{} and λ_{2}^{}are 57nmcm^{1/2} and 74nmcm^{1/2} respectively, which are much larger than the 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 linewidthnarrowing components.
The crystal holder (free) and oven & Temperature Controller (for NCPM,OPO,OPA applications) are available for BBO & LBO.
ARcoatings
LASERMA provides the following ARcoatings: * Dual Band ARcoating (DBAR) of LBO for SHG of 1064nm. · low reflectance (R<0.2% at 1064nm and R<0.5% at 532nm ); · high damage threshold (>500MW/cm^{2}at both wavelengths); · long durability. * Broad Band ARcoating (BBAR) of LBO for SHG of tunable lasers. * Other coatings are available upon request.
LASERMA Warranty on LBO Specifications
* Dimension tolerance: (W±0.1mm)x(H±0.1mm)x(L+0.5/0.1mm) (L≥2.5mm) (W±0.1mm)x(H±0.1mm)x(L+0.1/0.1mm) (L<2.5mm) * Clear aperture: central 90% of the diameter * No visible scattering paths or centers when inspected by a 50mW green laser * Flatness: less than λ/8 @ 633nm * Transmitting wavefront distortion: less than λ/8 @ 633nm * Chamfer: ≤0.2mmx45° * Chip: ≤0.1mm * Scratch/Dig code: better than 10/ 5 to MILPRF13830B * Parallelism: better than 20 arc seconds * Perpendicularity: ≤5 arc minutes * Angle tolerance: Δθ≤0.25°, ΔΦ≤0.25° * Damage threshold[GW/cm^{2} ]: >10 for 1064nm, TEM00, 10ns, 10HZ (polished only) >1 for 1064nm, TEM00, 10ns, 10HZ (ARcoated) >0.5 for 532nm, TEM00, 10ns, 10HZ (ARcoated) * Quality Warranty Period: one year under proper use.
NOTES
1. LBO has a very low susceptibility to moisture. Users are advised to provide dry conditions for both the use and preservation of LBO. 2. Polished surfaces of LBO requires precautions to prevent any damage. 3. LASERMA engineers can select and design the best crystal for you, if the main parameters of your laser are provided, such as energy per pulse, pulse width and repetition rate for a pulsed laser, power for a cw laser, laser beam diameter, mode condition, divergence, wavelength tuning range, etc. 4. For thin crystal, LaserMa can provide free holder for you.
 