| Introduction
Lithium triborate (LiB 3 O 5 or LBO) has the following exceptional properties that make it a very important nonlinear crystal: 
CLASER LBO has following advance:
- absorption: <100ppm/cm @1064nm <50ppm/cm for high power laser aoolication
- High damage coating for high power cw laser.
- Large quantity standard products in stock
- Low price
Lbo crystals advanced
- broad transparency range from 160nm to 2600nm;
- high optical homogeneity ( d n » 10 -6 /cm) and being free of inclusion;
- relatively large effective SHG coefficient (about three times that of KDP);
- high damage threshold (18.9 GW/cm 2 for a 1.3ns laser at 1053nm);
- wide acceptance angle and small walk-off;
- type I and type II non-critical phase matching (NCPM) in a wide wavelength range;
- spectral NCPM near 1300nm.
LBO is grown with the flux method. It is a negative biaxial crystal, with the principal axes X, Y, and Z (n z >n y >n x ) parallel to the crystallographic axes a, c, and b, respectively.
Structural and Physical Properties:
Crystal Structure: |
Orthorhombic, Space group Pna2 1 , Point group mm2 |
Cell Parameters: |
a=8.4473 Å , b=7.3788 Å , c=5.1395 Å , Z=2 |
Melting point: |
About 834 ° C |
Optical homogeneity: |
d n » 10 -6 /cm |
Mohs hardness: |
6 |
Density: |
2.47 g /cm 3 |
Thermal expansion coefficients: |
a x =10.8x10 -5 /K, a y = -8.8x10 -5 /K, a z =3.4x10 -5 /K |
Hygroscopic susceptibility: |
Low |
Absorption coefficient: |
<0.01%/cm at 1064nm |
Thermal conductivity: |
3.5 W/mK |
Linear Optical Properties:
Transparency range: |
155-3200 nm |
Sellmeier equations:
( l in m m) |
n 2 x =2.454140+0.011249 /( l 2 -0.011350)-0.014591 l 2 -6.60x10 - 5 l 4
n 2 y =2.539070+0.012711/ ( l 2 -0.012523)-0.018540 l 2 +2.00x10 -4 l 4
n 2 z =2.586179+0.013099/( l 2 -0.011893)-0.017968 l 2 -2.26x10 -4 l 4 |
Refractive indices:
at 1064 nm
at 532 nm
at 266 nm |
n x = 1.5656, n y = 1.5905, n z =1.6055
n x = 1.5785, n y = 1.6065, n z =1.6212
n x = 1.5973, n y = 1.6286, n z =1.6444 |
Therm-optic coefficients:
(/K, l in m m) |
Dn x /dT = -1.8x 10 -6
dn y /dT = -13.6 x 10 -6
Dn z /dT = (-6.3-2.1 l ) x 10 -6 |
Nonlinear Optical Properties:
NLO coefficients: |
d 31 =1.05 ± 0.09 pm/V
d 32 = -0.98 ± 0.09 pm/V
d 33 =0.05 ± 0.006 pm/V |
Effective nonlinearity expressions |
d ooe =d 32 cos f (in XY plane) |
d eeo =d 31 cos 2 q +d 32 sin 2 q (in XZ plane) |
d oeo =d 31 cos q (in YZ plane) |
d eoe =d 31 cos 2 q +d 32 sin 2 q (in XZ plane) |
Damage threshold:
at 1064nm
at 532nm |
9GW/cm 2 (9 ns); 19 GW/cm 2 (1.3 ns)
2.2 GW/cm 2 (10 ns); 45 GW/cm 2 (100 ps)
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LBO has the highest damage threshold in all the commonly-used inorganic NLO crystals. Therefore, it is the best candidate for high average power SHG and other nonlinear optical processes.
Damage Threshold at 1053nm |
Crystal |
Energy Density (J/cm 2 ) |
Power Density (GW/cm 2 ) |
Ratio |
KTP
KDP
BBO
LBO |
6.0
10.9
12.9
24.6 |
4.6
8.4
9.9
18.9 |
1.00
1.83
2.15
4.10 |
LBO's applications
- SHG and THG for middle and high power Nd: lasers at 1064nm for medical, industrial and military applications;
- SHG for Ti:Sapphire, Alexandrite and Cr:LiSAF lasers;
- SHG and THG of high power Nd: lasers at 1342nm & 1319nm for red and blue laser
- SHG for the Nd: Lasers at 914nm & 946nm for blue laser.
- The VUV output at 187.7 nm is obtained by sum-frequency generation.
- NCPM SHG over a broad wavelength range from 900nm-1700nm was measured.
- Phase matching process cutoff: SHG-554 nm fundamental, THG-794 nm, SFM-down to 160 nm.
- Optical Parametric Amplifiers (OPA) and Oscillators (OPO) application;
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 in a wide wavelength range from 551nm to about 3000nm. LBO is the first choice for making doubler or tripler for lasers such as Nd:YAG where high power density, high stability, and long time operation are required.
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SHG tuning curves of LBO |
NCPM temperature tuning curves of LBO |
Non-Critical Phase-Matching
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. As shown, type I and type II non-critical phase-matching can be reached along x-axis ( q =90 ° , f =0 ° ) and z-axis ( q =0 ° , f =0 ° ) at room temperature, respectively.
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. with good output stability and beam quality. |
Properties of type I NCPM SHG at 1064nm |
NCPM Temperature |
148 ° C |
Acceptance Angle |
52 mrad-cm 1/2 |
Walk-off Angle |
0 |
Temperature Bandwidth |
4 ° C-cm |
Effective SHG Coefficient |
2.69 d 36 (KDP) |
LBO's OPO and OPA
LBO is an excellent NLO crystal for OPOs and OPAs with a widely tunable wavelength range and high powers. 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.
LBO Specifications
Transmitting wavefront distortion: less than l /8 @ 633nm
Dimension tolerance: (W ± 0.1mm )x(H ± 0.1mm )x(L+0.2/ -0.1mm )
Clear aperture: central 90% of the diameter
No visible scattering paths or centers when inspected by a 50mW green laser
Flatness: l /8 @ 633nm
Scratch/Dig code: 10/ 5 to MIL-O -13830A
Parallelism: better than 20 arc seconds
Perpendicularity: 5 arc minutes
Angle tolerance: D q < ± 0.2 ° , D f < ± 0.2 °
Coating: High Damage Threshold DBAR and THG coating for 1064nm laser
Quality Warranty Period: one year under proper use.
NOTE
- LBO has a very low susceptibility to moisture. Users are advised to provide dry conditions for both the use and preservation of LBO.
- Polished surfaces of LBO requires precautions to prevent any damage.
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