All About CLBO (Cesium Lithium Borate) Crystals
What are CLBO Crystals
Cesium lithium borate crystal (chemical formula CsLiB6O10), CLBO crystal for short, is a novel type of nonlinear crystal material (nonlinear optical crystals are crystals that show secondary or higher nonlinear optical effects in response to strong laser electric fields. Nonlinear crystals are key materials for laser frequency conversion, modulation, deflection, Q switching, and other technologies, discovered in the 1990s. It has excellent comprehensive properties, such as a short UV cutoff wavelength of 180nm, an effective nonlinear optical coefficient deff that is twice that of KDP, and the ability to achieve phase matching for the second, third, fourth, and fifth harmonic generation of Nd:YAG lasers. In addition, CLBO crystals are particularly suitable for the fourth harmonic generation (FHG) of high-power Nd: YAG lasers, obtaining 266nm ultraviolet laser output. Cesium lithium borate also features a small energy walk-off angle and low ultraviolet absorption, high laser damage threshold, and large-sized single crystals can be easily obtained. Due to the absence of the two-photon absorption commonly observed in BBO crystals and KDP crystals, CLBO is not saturated for high-power generation. These properties give the crystal good application prospects in the field of all-solid-state ultraviolet lasers.
This article offers a comprehensive introduction to CLBO crystals, including the properties, data sheets, advantages, and applications of cesium lithium borate as a nonlinear crystal material. This article also contains a comparison of CLBO with the other two common NLO crystals (BBO crystals and LBO crystals).
Properties and Advantages of CLBO Crystals
CLBO crystals have the following optical, physical, and chemical properties. The critical technical parameters are listed in the table below:
| Chemical and Structural Properties | |||
| Chemical Formula | CsLiB6O10 | Crystal Structure | Tetragonal, Space group Ⅰ 42m |
| Lattice Constants | a = b = 10.494 Å, c = 8.939 Å | Symmetry | z=4 |
| Melting Point | Around 844.5° | Density | 2.461 g/cm3 |
| Molecular Mass | 364.706 | ||
| Optical and Nonlinear Optical Properties | |||
| Transmission Wavelength Range | 180-2750nm | Walk-off Angle | 1.78 °at 1064nm; 1.83 °at 532nm; 0.98 °at 488nm |
| Effective NLO Coefficients | 1.01 pm/V at 532nm; 1.16 pm/V at 488nm; 0.95 pm/V at 1064nm |
NLO Coefficients | deff (Ⅰ) = d36 sinθmsin(2 Ф) ; deff (Ⅱ) = d36 sin(2θm) sin(2 Ф) |
| Angle Acceptance | 1.02 mrad·cm at 1064 nm; 0.49 mrad·cm at 532 nm; 0.84 mrad·cm at 488 nm |
Temperature Acceptance | 9.4℃·cm |
| Spectral Acceptance | 7.03 nm·cm at 1064 nm; 0.13 nm·cm at 532 nm; 0.09 nm·cm at 488 nm |
Sellmeier Equations (λ in μm) | CLBO at 20 ℃
|
CLBO is especially appreciated for various applications because it combines the following features and advantages:
-Shortwave cut-off wavelength can reach 180nm
-High conversion efficiency for the frequency quadrupling and frequency quintupling of 1064nm Nd:YAG laser
-Excellent for ultraviolet nonlinear applications
-High nonlinear coefficient (about twice that of KDP)
-Large acceptance angle and small walkoff angle (which is important for beam quality)
-193nm vacuum UV (VUV) light output can be obtained through phase matching
-Short growth cycle, large size crystals can be grown
-High laser damage threshold
One of the initial obstacles faced by traditional nonlinear crystals was their limited lifespan, especially in harsh conditions where the NLO crystals are subject to strong UV exposure. Over time, these crystals tend to degrade, reducing their efficiency and overall performance. This degradation not only means more frequent replacement, but also poses a potential risk in precision-demanding applications where consistent output is critical. In contrast, CLBO crystals have an impressive resistance to UV-induced degradation.
Another area where CLBO outperforms its predecessors is in phase matching. In the field of nonlinear optics, phase matching (click here to learn more about phase matching) is critical. Phase matching is a condition where the different light waves involved in the nonlinear interaction stay in synchronization with each other as they travel through a material. If the interacting waves aren’t matched, this causes destructive interference, and the effect cancels out or becomes very weak, the energy transfer becomes inefficient, and the nonlinear effects (like frequency doubling, mixing, etc.) won’t work well. Because different frequencies of light usually travel at different speeds in a material due to dispersion, phase matching doesn’t happen automatically, phase matching can be achieved purposefully using methods like angle tuning, temperature tuning, and quasi-phase matching (QPM). Conventional crystals often have limitations in achieving perfect phase matching, leading to suboptimal results and wasted energy. However, CLBO crystals are engineered to have enhanced phase-matching capabilities. This inherent quality enables them to provide the maximum energy output for the energy they receive, ensuring that the system operates at maximum efficiency and delivers the best results. Phase matching in CLBO is achieved via angle tuning, which means adjusting the crystal orientation to match the phase velocities of the interacting light waves. CLBO supports Type I and Type II phase matching.
Finally, as technological applications become more complex and demanding, material stability, especially under varying thermal conditions, becomes a critical issue. Temperature fluctuations can cause catastrophes in optical processes, leading to inconsistent output and even the risk of damage. Conventional nonlinear crystals, while capable, often struggle to cope with extreme temperature changes. In stark contrast, CLBO crystals are renowned for their exceptional thermal stability. They remain unaffected by extreme heat or cold, providing consistent performance regardless of environmental conditions.
Applications of Nonlinear CLBO Crystals
1. High-Power UV Laser Generation
Second Harmonic Generation (SHG) (Click here to learn about second harmonic generation) and Fourth Harmonic Generation (FHG) of Nd: YAG lasers:
- 1064nm to 532nm (SHG)
- 532nm to 266nm (FHG)
Used in high-power laser systems where deep UV light is needed.
Example: Ultraviolet laser sources for photolithography, especially for micromachining or semiconductor inspection.
2. Sum-Frequency and Difference-Frequency Generation
Ideal for combining visible and infrared lasers to create tunable UV sources.
Useful in systems where broad wavelength tunability is required.
Application: Spectroscopy systems and optical parametric oscillators (OPOs) generating UV wavelengths.
3. Laser Micromachining
Because of CLBO’s ability to convert to UV light with high precision, it’s used in:
- Cutting or engraving materials that absorb UV well
- Structuring of polymers, glasses, or semiconductors
Industries: Electronics, microfluidics, solar panel manufacturing
4. Nonlinear Optical Devices
CLBO serves in nonlinear frequency conversion modules:
- Doublers (SHG)
- Triplers and quadruplers (THG, FHG)
- UV light sources for scientific or industrial instruments
Example: UV pump sources for dye lasers or optical parametric devices.
5. UV Spectroscopy & Laser-Induced Fluorescence
The UV output generated with CLBO is ideal for exciting fluorescence in:
- Biological samples
- Trace element detection
- Molecular spectroscopy
Benefit: CLBO-generated UV offers sharper excitation with minimal background noise.
6. Semiconductor and Photonics Inspection
UV lasers from CLBO are used in optical inspection tools that detect sub-micron defects or patterns on silicon wafers or photonic chips.
Example: Wafer inspection tools in cleanroom environments.
CLBO Crystal Storage and Handling
A serious challenge posed to the user and manufacturer of CLBO crystals is their high hygroscopicity. Cesium lithium borate single crystals often crack at room temperature in ambient air, limiting their application in devices. The cracking of high-quality CLBO crystals stems from the anisotropic corrosive effect of water vapor in the air. Water molecules attack the crystal surface directionally, influenced by its crystal structure. Therefore, it is strongly recommended to strictly control the humidity of the operating environment to prevent CLBO crystals from deliquescing.
Hangzhou Shalom EO is a specialized supplier of custom CLBO crystals. We have developed a low-humidity workshop for the processing of cesium lithium borate crystals. The humidity of the environment is kept low to preserve the quality of our CLBO crystals. We also package and transport our CLBO crystals with stringent protection treatment to avoid deliquescence. Our cesium lithium borate crystals also feature outstanding optical performance, like high frequency conversion efficiency, high laser damage threshold, wide optical response wavelength range. The crystals are available as ingots, blanks, polished, and coated.
We are capable of providing CLBO crystals of large sizes and superior precision standards, including:
- ≤lambda/6@633nm surface flatness
- Δθ≦0.25°, ΔФ≦0.25 ° angular tolerance
- 10/5 S/D surface quality
- Dimensional olerance ±0.1mm (L) x ±0.1mm (W) x +0.1mm/-0.1mm (L<2.5mm)/+0.5mm/-0.1mm (L≥2.5mm)
- Discover more about Shalom EO’s CLBO crystals.
Shalom EO's CLBO Crystals/Cesium Lithium Borate Crystals
Comparison of LBO, BBO, and CLBO Crystals
LBO crystals, BBO crystals, and CLBO crystals are all widely used nonlinear optical crystals, and they have important application value in the field of laser technology. The following is a detailed overview of these three crystals:
1. LBO Crystal
-Characteristics of LBO Crystals:
Full name: Lithium triborate (LiB3O5) crystal
Structure: Monoclinic structure, non-centrosymmetric crystal, space group C2 (point group 2). The crystal structure is composed of triborate (BO3) and lithium (Li) ions. The BO3 groups are arranged in a triangle to form a six-membered ring in the crystal structure, and the Li ions occupy the interstitial positions between the BO3 groups.
Density: 2.48g/cm³
Mohs hardness: 6
Transmittance range: 0.16~2.6μm
Large nonlinear optical coefficient
High optical damage threshold (about 4.1 times that of KTP, 1.83 times that of KDP, and 2.15 times that of BBO)
Good chemical stability and deliquescence resistance
-Applications of LBO Crystals
It can be used for the frequency doubling and tripling of 1.06μm lasers to achieve type I and type II phase matching.
It can be used to make laser frequency doublers and optical parametric oscillators.
-Crystal Growth Method of LBO Crystals
High temperature solution method: can grow optical quality single crystals.
Czochralski method: A mature technology for growing large, high-quality single crystals.
Flux method: involves dissolving the starting material in a flux and slowly cooling the solution to form crystals.
Top crystal solution growth (TSSG) method: Popular for its ability to produce high-quality crystals with low defect density.
2. BBO Crystal
-Characteristics of BBO Crystals
Full name: Low temperature phase barium metaborate (β-BaB2O4) crystal, or beta-BBO crystal
Invention: Invented in 1979 by the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences.
Asymmetric center crystal with excellent nonlinear optical effect and outstanding electro-optical effect.
The frequency modulation range is wide, and it performs particularly well in the ultraviolet band.
-Applications of BBO Crystals
It can be made into a fully solid-state tunable laser with a continuously adjustable wavelength from visible to near infrared.
Second, Third, Fourth, and Fifth Harmonic Generation of Nd: YAG Lasers
OPO of 532nm pumped lasers for output ranging from 680 nm to 2400 nm
OPO and OPA of 355nm Nd:YAG pumped lasers
Quantum Entanglement
3. CLBO Crystal
-Characteristics of CLBO Crystals
Full name: Cesium lithium borate (CsLiB6O10) crystal
CLBO crystal was created by Dr. Mori and Dr. Sasaki of Osaka University in 1993.
Excellent nonlinear optical properties: CLBO crystals are widely used in the field of ultraviolet laser frequency doubling and deep ultraviolet sum frequency, and can perform quadruple and quintuple frequency doubling of the 1064nm laser output by the Nd:YAG laser.
High damage threshold: CLBO crystals have a damage threshold of up to 25GW/cm2 and excellent stability, which can play an important role in high-power laser applications.
Wide light transmission range: The light transmission range of CLBO crystal is very wide, extending from 180nm to 2750nm. This feature enables it to play a key role in the generation of lasers of various wavelengths.
Smaller walk-off angle and larger acceptable angle: CLBO crystal has a smaller walk-off angle and a larger acceptable angle, and can play an important role in high-power UV solid-state lasers.
Larger spectral bandwidth and temperature bandwidth: CLBO crystals have larger spectral bandwidth and temperature bandwidth, and can play an important role in a variety of environments.
Applications of CLBO Crystals
-Harmonic generation of Nd: YAG lasers or other lasers doped with Nd ions
-SHG, THG of Ti:sapphire and Alexandrite lasers
-laser output of DUV or VUV wavelengths such as 193nm or 266nm
-micro-processing
-Semiconductor lithography, semiconductor inspection
-Biomedical Science
-UV-LIDAR
In summary, LBO, BBO, and CLBO crystals have their characteristics and play an important role in the field of laser technology. Their different characteristics and applications enable researchers to select appropriate crystals to achieve specific optical effects as needed.
A Comparison Chart of CLBO, BBO, and LBO Crystals
Crystals |
Optical Properties |
Physical/Chemical Properties |
Applications |
CLBO |
Transmission cut-off range up to 180nm, large spectral and temperature bandwidth, good angle tolerance, small walk off angle |
The growth cycle is short, and large crystals can be grown, but it is highly hygroscopic. |
High-power Nd:YAG laser system quadrupling; microprocessing, semiconductor lithography, and other fields |
BBO |
Wide light transmission range, wide phase matching range, large harmonic generation coefficient, high laser damage threshold |
Stable crystal structure, broad phase matching range, large SHG coefficient |
Frequency doubling of Nd:YAG crystals; research and development of high-precision laser technologies such as optical parametric amplifiers and optical parametric oscillators |
LBO |
Wide transmission spectrum range, high nonlinear coupling characteristics, and high laser damage threshold |
Good optical uniformity, stable chemical and mechanical processing performance |
High-power frequency doubling, tripling, quadrupling, etc.; parametric oscillation, parametric amplification, optical waveguide, etc. |
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