Nonlinear Crystals

Product Introduction

Lithium triborate (LiB₃O₅, LBO) is an excellent nonlinear optical crystal discovered by the Institute of Research on the Structure of Matter, Chinese Academy of Sciences. The patent for this crystal was awarded the 1999 China Invention Patent Gold Award by the State Intellectual Property Office and the World Intellectual Property Organization.

Key Advantages
  • Wide transmittance range (160-2600 nm, see Figure 1)
  • Excellent optical uniformity (δn ≈ 10⁻⁶/cm) and low internal envelope
  • High frequency conversion efficiency (three times that of KDP crystals)
  • High damage threshold
  • Wide acceptance angle and low walk-off angle
  • Wide wavelength range for Type I and II non-critical phase matching (NCPM)
  • Spectral non-critical phase matching (NCPM) close to 1300 nm
offer
  • Strict quality control
  • Large crystal sizes, with clear areas up to 55×55 mm² and lengths up to 60 mm
  • AR coating, bracket assembly, and re-polishing services
  • Sufficient inventory
  • Fast delivery (15 working days for polished crystals, 20 working days for coated products)
Room-Temperature SHG and THG Properties of LBO Crystals

LBO crystals can be used for phase matching of the second and third harmonics of Nd:YAG and Nd:YLF lasers, achieving both Type I and Type II matching. At room temperature, over a wide wavelength range from 551 nm to 2600 nm, the XY and XZ planes (see Figure 2) achieve the highest effective harmonic generation coefficients (effective second-order nonlinear optical coefficients are shown in Table 2). The best Type II matching (effective second-order nonlinear optical coefficients are shown in Table 2) is achieved on the YZ and XZ planes (see Figure 2). Nd:YAG lasers can achieve second harmonic generation (SHG) conversion efficiencies exceeding 70% and 30% in pulsed and continuous wave modes, respectively, and third harmonic generation (THG) conversion efficiencies exceeding 60%.

Applications of LBO Crystal Double and Triple Frequency Harmonization
  • For a 2W mode-locked Ti:sapphire laser (<2 ps, 82 MHz), frequency harmonic generation using an LBO crystal can produce 395 nm laser output power exceeding 480 mW.
  • A Q-switched Nd:YAG laser frequency-doubled using an 18 mm Type II LBO crystal can achieve green light output power exceeding 80 W.
  • A LD-pumped Nd:YLF laser (>500 μJ @ 1047 nm, <7 ns, 0-10 kHz) using a 9 mm LBO crystal can achieve a frequency harmonic generation conversion rate exceeding 40%.
  • LBO crystal sum frequency effects can be used to produce vacuum ultraviolet light at a wavelength of 187.7 nm.
  • Intracavity frequency tripled (THG) of a Q-switched Nd:YAG laser can produce a diffraction-limited beam with an output pulse energy of 2 mJ @ 355 nm.
Non-critical Phase Matching in LBO Crystals

As shown in Table 3, non-critical phase matching (NCPM) in LBO crystals offers advantages such as zero walk-off, a wide acceptance angle, and a high efficiency factor. LBO can be optimized by fully utilizing these characteristics. Nd:YAG lasers using NCPM LBO crystals achieve second harmonic conversion efficiencies exceeding 70% in pulsed mode and over 30% in continuous wave mode, with excellent beam quality and stable output. As shown in Figure 3, LBO crystals can achieve Type I and Type II non-critical phase matching in the X and Z axes, respectively, at room temperature.

OPO and OPA of LBO Crystals

Extracavity frequency doubling of a 25 W Antares mode-locked Nd:YAG laser (76 MHz, 80 ps) can produce 532 nm laser light with an average power exceeding 11 W.
Frequency doubling of a medical multimode Q-switched Nd:YAG laser can produce 20 W of green light. Higher input power yields higher output power.

OPOs and OPAs in LBO Crystals

LBO crystals, with their wide tuning wavelength range and high damage threshold, are excellent nonlinear optical crystals for applications in optical parametric amplifiers (OPAs) and optical parametric oscillators (OPOs). Numerous reports have been published on OPAs and OPOs pumped by doubled and tripled Nd:YAG lasers and 308 nm XeCl excimer lasers. The type I and II phase matching and NCPM properties of LBO crystals offer broad scope for in-depth research and application in the field of OPOs and OPAs. Figure 4 shows the theoretically calculated tuning curves of room-temperature type I OPOs in LBO crystals pumped by doubled, tripled, and quadrupled Nd:YAG lasers in the XY plane. Figure 5 shows the tuning curves of type II OPOs in LBO crystals pumped by doubled and tripled Nd:YAG lasers in the XZ plane.

Application of LBO Crystals in OPO and OPA
  • OPOs pumped at 355 nm have a high overall conversion efficiency, tunable to wavelengths between 540 and 1030 nm.
  • Type I LBO crystal OPAs pumped at 355 nm have been reported to achieve a 30% pump-to-signal energy conversion efficiency.
  • Type II matched NCPM-OPO systems pumped at 308 nm XeC1 excimer lasers can achieve an energy conversion efficiency of 16.5%. A wide tunable wavelength range can be achieved by varying the pump source and temperature tuning.
  • By varying the pump source and temperature tuning, even wider wavelength tuning can be achieved.
  • Using NCPM technology, pumped by a 532 nm harmonic of an Nd:YAG laser, and with temperature tuning between 106.5 and 148.5°C, a Type I LBO crystal OPA can achieve a tunable wavelength range between 750 and 1800 nm. Using a type II NCPM LBO as an optical parametric generator (OPG) and a type I critical phase BBO crystal as an optical parametric amplifier (OPA), and pumped with a 4.8 mJ, 30 ps, 354.7 nm laser, a narrow linewidth (0.15 nm) and a high pump-to-signal energy conversion rate (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 Noncritical Phase Matching of LBO Crystals

LBO crystals can achieve not only angularly variable noncritical phase matching (NCPM) but also spectrally variable noncritical phase matching (SNCPM). As shown in Figure 2, the phase matching inflection 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 these two locations exhibits a large spectral acceptance Δλ. The calculated Δλ is 57 nm·cm at λ1 and 74 nm·cm at λ2, both exceeding the Δλ of other NLO crystals. These spectral properties of LBO crystals are ideal for frequency doubling of broadband coherent radiation around 1.3 μm, such as the output of some diode lasers and some OPA/OPOs without linewidth narrowing components.

Antireflection Coatings
  • Dual-wavelength antireflection coatings (DBAR) for 1064 nm frequency doubling and triple-wavelength antireflection coatings for 1064 nm frequency tripling are available.
  • These AR coatings offer 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) can also be applied based on application requirements.
  • Broadband antireflection coatings (BBAR) are suitable for frequency doubling of tunable lasers.
  • Choose between IBS and IAD coating technologies based on customer application requirements.
  • High laser damage threshold. Long service life. Custom coating systems available.
LBO crystal specifications

Note:

  • LBO crystals are easily hygroscopic. We recommend that you use and store them in a dry environment.
  • Please handle with care to avoid damaging the polished surface of the LBO crystal.
  • We can customize LBO crystals to meet your specific needs.
  • We recommend suitable crystal specifications based on the laser’s key performance parameters, such as pulse energy, pulse width, and repetition rate for pulsed lasers, power for continuous lasers, as well as beam diameter, mode conditions, divergence angle, and tunable wavelength range.
  • For thin crystals, we offer free mounting brackets.