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NOL crystal
optical crystal
LBO
Product Introduction
Lithium triborate (LiB₃O₅, LBO) is an excellent nonlinear optical crystal.
Main Advantages
Wide transmittance wavelength range (160 - 2600 nm, see Figure 1)
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Product description
What Zhongce Technology Can Provide
Figure 4. Tuning Curve of Type I OPO of LBO Crystal Figure 5. Tuning Curve of Type II OPO of LBO Crystal
Anti-Reflection Coating
Product Introduction
Lithium triborate (LiB₃O₅, LBO) is an excellent nonlinear optical crystal.
Main Advantages
- Wide transmittance wavelength range (160 - 2600 nm, see Figure 1)
- Good optical homogeneity (Δn ≈ 10⁻⁶/cm), with few internal inclusions
- High frequency doubling conversion efficiency (equivalent to 3 times that of KDP crystal)
- High damage threshold
- Wide acceptance angle and small walk-off angle
- Wide wavelength range for Type I and Type II non-critical phase matching (NCPM)
- Spectral non-critical phase matching (NCPM) is close to 1300 nm
What Zhongce Technology Can Provide
- Strict quality control
- Large-sized crystals, with the light-transmitting surface up to 55×55 mm² and the length up to 60 mm
- Anti-reflection coating (AR-coating) deposition, holder assembly and re-polishing and coating services
- Ample inventory
- Fast delivery (15 working days for polished wafers and 20 working days for coated products)
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Crystal Structure
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Orthorhombic system, space group Pna2₁, point group mm²
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Unit Cell Parameters
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a = 8.4473 Å, b = 7.3788 Å, c = 5.1395 Å, Z = 4
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Melting Point
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Approximately 834 °C
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Mohs Hardness
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6 Mohs
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Density
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2.47 g/cm³
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Thermal Conductivity
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3.5 W/m/K
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Coefficient of Thermal Expansion
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αₓ = 10.8×10⁻⁵ /K, αᵧ = -8.8×10⁻⁵ /K, αz = 3.4×10⁻⁵ /K
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Transmittance Wavelength Range
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160 - 2600 nm
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SHG Phase Matching Range
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551 - 2600 nm (TypeⅠ) 790 - 2150 nm (TypeⅡ)
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Thermo-Optic Coefficient
(/℃, λ in μm)
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dnₓ/dT = -9.3×10⁻⁶
dnᵧ/dT = -13.6×10⁻⁶
dnz/dT = (-6.3 - 2.1λ)×10⁻⁶
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Absorption Coefficient
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< 0.1%/cm @ 1064 nm, < 0.3%/cm @ 532 nm
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Acceptance Angle
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6.54 mrad·cm (Ф, TypeⅠ, 1064 SHG)
15.27 mrad·cm (θ, TypeⅡ, 1064 SHG)
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Temperature Bandwidth
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4.7℃·cm (TypeⅠ, 1064 SHG)
7.5℃·cm (TypeⅡ, 1064 SHG)
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Acceptance Spectral Width
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1.0 nm·cm (TypeⅠ, 1064 SHG)
1.3 nm·cm (TypeⅡ, 1064 SHG)
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Walk-off Angle
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0.60° (TypeⅠ, 1064 SHG)
0.12° (TypeⅡ, 1064 SHG)
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NLO Coefficient
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deff(Ⅰ) = d₃₂cosФ (TypeⅠ, XY plane)
deff(Ⅰ) = d₃₁cos2θ + d₃₂sin2θ (TypeⅠ, XZ plane)
deff(Ⅱ) = d₃₁cosθ (TypeⅡ, YZ plane)
deff(Ⅱ) = d₃₁cos2θ + d₃₂sin2θ (TypeⅡ, XZ plane)
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Non-zero Nonlinear Optical Coefficient
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d₃₁ = 1.05 ± 0.09 pm/V
d₃₂ = -0.98 ± 0.09 pm/V
d₃₃ = 0.05 ± 0.006 pm/V
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Sellmeier Equation
(λ unit μm)
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nₓ² = 2.454140 + 0.011249 / (λ² - 0.011350) - 0.014591λ² - 6.60 × 10⁻⁵ λ⁴
nᵧ² = 2.539070 + 0.012711 / (λ² - 0.012523) - 0.018540λ² + 2.00 × 10⁻⁴ λ⁴
nz² = 2.586179 + 0.013099 / (λ² - 0.011893) - 0.017968 λ² - 2.26 × 10⁻⁴ λ⁴
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Figure 1. Transmission Curve of LBO
SHG and THG Characteristics of LBO Crystal at Room Temperature
The LBO crystal can be used for second and third harmonic frequency phase matching of Nd:YAG and Nd:YLF lasers, both Type I and Type II matching are applicable. At room temperature, within a relatively large wavelength range from 551 nm to 2600 nm, Type I matching with the maximum effective frequency doubling coefficient can be achieved on the XY plane and XZ plane (see Figure 2) (the effective second-order nonlinear optical coefficient is shown in Table 2). The best Type II matching of the LBO crystal (the effective second-order nonlinear optical coefficient is shown in Table 2) is on the YZ and XZ planes (see Figure 2). It is reported that using the LBO produced by Zhongce Technology, the second harmonic conversion efficiency of Nd:YAG laser in pulse mode and continuous mode can be greater than 70% and greater than 30% respectively, and the third harmonic conversion efficiency is greater than 60%.
Figure 2. SHG Tuning Curve of LBO Crystal
Applications of Second and Third Harmonic Generation of LBO Crystal
- For a 2W mode-locked Ti:sapphire laser (< 2 ps, 82 MHz), using the LBO crystal for frequency doubling can output a 395 nm laser with a power greater than 480 mW.
- Using an 18 mm Type II LBO crystal for frequency doubling of a Q-switched Nd:YAG laser can obtain a green light output with a power greater than 80 W.
- The frequency doubling conversion efficiency of an LD-pumped Nd:YLF laser (> 500 μJ @ 1047 nm, < 7 ns, 0 - 10 KHz) using a 9 mm LBO crystal can be greater than 40%.
- Using the sum frequency effect of the LBO crystal can output vacuum ultraviolet light with a wavelength of 187.7 nm.
- Intracavity third harmonic generation of a Q-switched Nd:YAG laser can obtain a diffraction-limited beam with an output pulse energy of 2 mJ @ 355 nm.
Non-Critical Phase Matching of LBO Crystal
As shown in Table 3, the non-critical phase matching (NCPM) of the LBO crystal has characteristics such as no walk-off, wide acceptance angle, and large effective coefficient. Making full use of this characteristic can enable the LBO to play its best role. Using a non-critical phase matching LBO crystal, the second harmonic conversion efficiency of the Nd:YAG laser in pulse mode is greater than 70%, and in continuous mode is greater than 30%, and the beam quality is good with stable output. As shown in Figure 3, at room temperature, the LBO crystal can obtain Type I and Type II non-critical phase matching in the X-axis and Z-axis directions respectively. Zhongce Technology has developed a heating furnace and temperature controller to cooperate with the application of non-critical phase matching of the LBO crystal. For detailed technical specifications, please refer to page 68.
| NCPM Temperature | 148 °C |
| Acceptance Angle | 52 mrad·cm |
| Walk-off Angle | 0 |
| Temperature Bandwidth | 4 °C·cm |
| Effective SHG Coefficient | 2.69×d36 (KDP) = 1.18 pm/V |
OPO and OPA of LBO Crystal
- External cavity frequency doubling of a 25 W Antares mode-locked Nd:YAG laser (76 MHz, 80 ps) can obtain a 532 nm laser with an average power of more than 11 W.
- Frequency doubling of a medical multimode Q-switched Nd:YAG laser can output 20 W of green light. The higher the input power, the higher the output power.
OPO and OPA of LBO Crystal
The LBO crystal has a relatively wide tuning wavelength range and a high damage resistance threshold, and it is an excellent nonlinear optical crystal suitable for applications in optical parametric amplifiers (OPA) and optical parametric oscillators (OPO). There are many reports of OPA and OPO using second and third harmonic Nd:YAG lasers and 308 nm XeCl excimer lasers as pump sources. The characteristics of Type I and Type II phase matching and NCPM of the LBO crystal provide broad space for in-depth research and application in the fields of OPO and OPA. Figure 4 is the theoretical calculation tuning curve of Type I OPO at room temperature of the LBO crystal pumped by the second, third and fourth harmonics of the Nd:YAG laser on the XY plane. Figure 5 is the tuning curve of Type II OPO of the LBO crystal pumped by the second and third harmonics of the Nd:YAG laser on the XZ plane.
Figure 4. Tuning Curve of Type I OPO of LBO Crystal Figure 5. Tuning Curve of Type II OPO of LBO CrystalApplications of LBO Crystal in OPO and OPA
- The OPO with a 355 nm pump light source has a high overall conversion efficiency and outputs a tunable wavelength in the range of 540-1030 nm.
- It is reported that the OPA of Type I LBO crystal pumped by 355 nm light can achieve a pump-to-signal energy conversion efficiency of 30%.
- The Type II matched NCPM-OPO system pumped by a 308 nm XeCl excimer laser can achieve an energy conversion efficiency of 16.5%. Suitable tunable wavelength ranges can be obtained through different pump sources and temperature adjustments.
- Broader wavelength tuning can be obtained according to different pump sources and temperature tuning.
- Using NCPM technology, with the 532 nm harmonic output of the Nd:YAG laser as the pump source, and under the temperature tuning range of 106.5-148.5 °C, the OPA of Type I LBO crystal can output a tunable wavelength in the range of 750-1800 nm.
- Using Type II NCPM LBO as an optical parametric generator (OPG) and Type I critical phase BBO crystal as an optical parametric amplifier (OPA), pumped by a 4.8 mJ, 30 ps, 354.7 nm laser, a relatively narrow linewidth (0.15 nm) and a high pump-to-signal energy conversion efficiency (32.7%) can be obtained. By increasing the temperature of the LBO crystal or rotating the BBO, light with a wavelength tuning range of 415.9-482.6 nm can be obtained.
Spectral Non-Critical Phase Matching of LBO Crystal
The LBO crystal can not only achieve non-critical phase matching (NCPM) with angle variation but also spectral non-critical phase matching (SNCPM). As shown in Figure 2, the phase matching turning points are located at λ1 = 1.31 μm, θ = 86.4°, φ = 0° (Type I) and λ2 = 1.30 μm, θ = 4.8°, φ = 0° (Type II). The phase matching at the above two positions has a relatively large spectral acceptance Δλ. The calculated Δλ is 57 nm·cm at λ1 and 74 nm·cm at λ2, both of which are larger than the Δλ of other NLO crystals. These spectral characteristics of the LBO crystal are very suitable for the frequency doubling of broadband coherent radiation at about 1.3 μm, such as the output of some diode lasers and some OPA/OPO without linewidth narrowing components.
Anti-Reflection Coating
- Double-wavelength anti-reflection coating (DBAR) for frequency doubling at 1064 nm and triple-wavelength anti-reflection coating for tripling at 1064 nm can be deposited.
- The anti-reflection coating has a low reflectivity (R < 0.2% @ 1064 nm, R < 0.5% @ 532 nm, R < 0.2% @ 355 nm). Ultra-low reflectivity (R < 0.05% @ 1064 nm, R < 0.1% @ 532 nm) anti-reflection coatings can also be deposited according to application requirements.
- Broadband anti-reflection coating (BBAR) is suitable for frequency doubling applications of tunable lasers.
- Select IBS or IAD coating technology according to customer application requirements.
- High laser damage resistance threshold.
- Long service life.
- Customized coating system services are available.
Specifications of LBO Crystal
| Size Tolerance |
(W ± 0.1 mm) × (H ± 0.1 mm) × (L + 0.5 / -0.1 mm) (L ≥ 2.5 mm)
(W ± 0.1 mm) × (H ± 0.1 mm) × (L + 0.1 / -0.1 mm) (L < 2.5 mm)
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| Effective Aperture for Light Transmission | 90% of the diameter of the central area |
| Flatness | λ/8 @ 633 nm |
| Transmission Wavefront Distortion | λ/8 @ 633 nm |
| Surface Finish | 10/5, Refer to MIL-PRF-13830B standard |
| Parallelism | 20" |
| Perpendicularity | 15' |
| Angle Deviation | Δθ ≤ 0.25°, ΔФ ≤ 0.25° |
| Chamfer | ≤ 0.2 mm × 45° |
| Edge Chipping | ≤ 0.1 mm |
| Damage Threshold |
> 10 GW/cm² @ 1064 nm, 10 ns, 10 Hz (polished wafer)
> 1 GW/cm² @ 1064 nm, 10 ns, 10 Hz (anti-reflection coating)
> 0.5 GW/cm² @ 532 nm, 10 ns, 10 Hz (anti-reflection coating)
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| Quality Assurance Period | One year (under normal use) |
Remarks:
- The LBO crystal is deliquescent. It is recommended that users use and store the crystal in a dry environment.
- Please operate carefully and do not damage the polished surface of the LBO crystal.
- LBO crystals can be customized according to customer requirements. Suitable crystal specifications can be recommended according to the main performance parameters of the provided laser, such as the pulse energy, pulse width, repetition frequency of the pulsed laser, the power of the continuous laser, as well as the beam diameter, mode conditions, divergence angle, tunable wavelength range and other conditions.
- For thin-film crystals, holders can be assembled for free.
