Lithium triborate (LiB3O5), commonly abbreviated as LBO, is a nonlinear optical crystal widely used in various applications involving frequency conversion of laser light. It is valued for its excellent optical properties, including high damage threshold, wide transparency range, and efficient nonlinear conversion capabilities.
Formula: The chemical formula of lithium triborate is LiB3O5.
Physical and optical properties:
Transparency range: LBO crystals have a broad transparency range, extending from approximately 160 nm to 2600 nm. This makes them suitable for use with a wide variety of laser wavelengths, from ultraviolet to infrared.
Nonlinear coefficients: LBO has relatively high nonlinear optical coefficients, which determine the efficiency of frequency conversion processes like second harmonic generation (SHG), third harmonic generation (THG), and sum-frequency generation (SFG).
Phase matching: LBO supports both type I and type II phase matching over a broad range of wavelengths. Phase matching is a condition necessary for efficient frequency conversion, and LBO's versatility in this regard allows for flexibility in designing nonlinear optical systems.
High damage threshold: LBO crystals can withstand high-intensity laser beams without damage, making them suitable for high-power laser applications.
Applications:
Second harmonic generation (SHG): LBO crystals are frequently used to double the frequency (halve the wavelength) of laser light. For example, a 1064 nm Nd:YAG laser can be converted to 532 nm green light.
Third harmonic generation (THG): They are also used for third harmonic generation, converting fundamental laser frequencies to even shorter wavelengths. For instance, a 1064 nm laser can be converted to 355 nm UV light.
Optical parametric oscillators (OPO): LBO crystals are used in OPOs to generate tunable laser light across a wide range of wavelengths by parametric down-conversion.
Sum-frequency generation (SFG): LBO is used to combine two different wavelengths of light into a single wavelength, particularly in applications requiring precise wavelength control.
Frequency doubling of femtosecond lasers: LBO crystals are ideal for frequency doubling of ultrafast lasers due to their broad phase-matching bandwidth and high damage threshold.
Advantages:
Wide transparency range: Allows for use with a broad spectrum of laser wavelengths.
High nonlinear conversion efficiency: Makes LBO effective for various nonlinear optical applications.
Thermal and mechanical stability: LBO crystals exhibit good thermal stability and mechanical robustness, ensuring reliable performance in various environmental conditions.
Wide phase-matching range: Facilitates efficient frequency conversion across different wavelengths and laser types.
Challenges:
Crystal growth and quality: High-quality LBO crystals require precise growth conditions and careful handling to avoid defects that could impair their optical properties.
Cost: The production and processing of high-quality LBO crystals can be expensive, which may limit their use in cost-sensitive applications.
Lithium triborate (LBO) crystals are indispensable in modern laser technology, providing efficient frequency conversion and enabling a wide range of applications from industrial laser systems to scientific research and medical devices. Their unique combination of properties makes them a versatile and valuable component in the field of nonlinear optics.