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LBO Single Crystal
Lithium triborate crystal
Lithium triborate crystal, known as LBO (LiB3O5), is one of the best nonlinear optical crystals.
Its' high damage threshold makes LBO crystals very suitable for harmonic generations of high-intensity laser radiation in a wide spectrum. LBO can get the highly efficient SHG of nanosecond, picosecond, CW and diode pumped Nd:YAG and Nd:YLF laser systems for R&D, medical, industrial and military applications.
In addition to high damage threshold, the superiority of LBO is also proven by the SHG of Ti:Sapphire, Cr:LiSAF and Alexandrite laser systems, as well as the optical parametric amplifiers and oscillators pumped by Excimer laser systems or harmonics of Nd:YAG systems.
With its good transmittance in the UV, LBO can achieve the tunable UV and VUV radiations by SFG.
Optical Properties:
Transmitting Range: 160nm ~ 2300nm
Phase Matching Range: 550 to 3000nm (I), 790nm ~ 2200nm (II)
Refractive Indices: @1064nm 1.5648(nx=b) 1.5904(ny=c) 1.6053(nz=a)
@532nm 1.5785 (nx=b) 1.6065(ny=c) 1.6212 (nz=a)
Sellmeier Equations (l in µm): x2 = 2.454140+0.011249/(l2-0.011350)-0.014591l2-6.60×10-5l4
ny2 = 2.539070+0.012711/( l2-0.012523)-0.018540l2+2.00×10-4l4
nz2 = 2.586179+0.013099/( l2-0.011893)-0.017968l2-2.26×10-4l4
Damage Threshold: 25GW/cm2 at 1.064um, 0.1ns pulse, 2.3J
Absorption Coefficient: a<0.1%/cm @1064nm
Nonlinear Optical Coefficients (pm/V) and Equation @1064nm:
d31=d15=0.85 d32=d24=-0.67 d33=0.04
deff (I, in XY plane) = d24cosf
deff (I, in XY plane) = d15cos2q + d24sin2q
deff(II, in YZ plane) = d15cosq
deff(II, in XZ plane) = d15cos2q + d24sin2q
Physical Properties:
Crystal Structure: Orthorhombic
Space group: Pna21
point group: mm2
Cell Parameters: a=8.4473Å, b=7.3788Å, c=5.1395Å, Z=2
Melting Point: 834°C
Mohs Hardness: 6
Density: 2.47g/cm3
Color: Colorless
Hygroscopic Susceptibility: no
Applications:
Frequency Conversion for Nd Laser Systems:
LBO is able to achieve phase matching 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 551 nm to about 3000nm. The effective SHG coefficients are as following: deff (I, XY place) = d32cosf; deff (I, in XZ plane) = d31cos2q + d32sin2q.
The optimum type II phase matching falls in the principal YZ and XZ planes with the effective SHG coefficient as: deff (II, in YZ plane)=d31cosq; deff (II, in XZ plane) = d31cos2q + d32sin2q.
SHG conversion efficiencies of more than 70% for pulsed and 30% for cw Nd:YAG laser, and THG conversion efficiency over 60% for pulsed Nd:YAG laser have been observed.
More than 480mW output at 395nm is generated by frequency doubling a 2W mode-locked Ti:Sapphire laser (<2ps, 82MHz). The wavelength range of 700-900nm is covered by a 5x3x8 mm3 LBO crystal.
Over 80W green output is obtained by SHG of a Q-switched Nd:YAG laser in a type II 18mm long LBO crystal.
The frequency doubling of a diode pumped Nd:YLF laser (>500µJ @ 1047nm, <7ns, 0-10KHz) reaches over 40% conversion efficiency in a 9mm long LBO crystal.
The VUV output at 187.7 nm is obtained by sum-frequency generation. 2mJ/pulse diffraction-limited beam at 355nm is obtained by intra-cavity frequency tripling a Q-switched Nd:YAG laser.
The phase matching angle for Nd:YAG laser system at maximum deff under room temperature is as following: q=11.4° and f=0° for Type I, q=90° and f=69.1° for Type II.
Non-Critical Phase-Matching Applications:
Non-Critical Phase-Matching (NCPM) of LBO is characterized by no walk-off effect, very wide acceptance angle and maximum effective coefficient. It helps LBO work in its optimal conditions. SHG conversion efficiencies of more than 70% for pulsed and 30% for cw Nd:YAG lasers have been obtained with good output stability and beam quality.
Properties of type I NCPM SHG at 1064nm:
NCPM Temperature 148°C
Acceptance Angle 52 mrad-cm1/2
Walk-off Angle 0
Temperature Bandwidth 4°C-cm
Effective SHG Coefficient 2.69d36(KDP)
Both type I and type II non-critical phase matching can be achieved along x-axis and z-axis at room temperature, respectively. LBO can reach both temperature NCPM and spectral NCPM (very wide spectral bandwidth) at 1300nm. This is favorable to the SHG of Nd lasers working at 1300nm for red light output.
LBO for OPA, OPO Applications:
LBO is an excellent NLO crystal for OPOs and OPAs with a widely tunable wavelength range and high powers. Both OPO and OPA, pumped by the SHG and THG of Nd:YAG laser and XeCl excimer laser at 308nm, have been reported. The unique properties of both type I and type II phase matching, along with the NCPM, leave room for both research and industry.
A rather high overall conversion efficiency and 540-1030nm tunable wavelength range were obtained with OPO pumped at 355nm.
Type I OPA pumped at 355nm with the pump-to-signal energy conversion efficiency of 30% has been reported.
Type II NCPM OPO pumped by a XeC1 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.
Pumped by a 4.8mJ, 30ps laser at 354.7nm, a narrow linewidth (0.15nm) and high pump-to-signal energy conversion efficiency (32.7%) were observed by using LBO with type II NCPM as an optical parametric generator (OPG) and BBO with type I critical phase matching as an OPA. By increasing the temperature of LBO and rotating BBO, we can obtain laser radiation from 415.9nm to 482.6nm.