BBO crystal — Excellent Nonlinear Crystal

Barium borate is an inorganic compound with the chemical formula Ba( BO2) 2. It can exist as a hydrate, a dried kind, a white powder, or a colorless crystal. There are 2 various types of the high-temperature stage (α-BBO) as well as low-temperature phase (β-BBO), as well as the phase transition temperature is 925 ℃.


β-BBO crystal development has actually been researched for more than two decades, and also has ended up being an extremely commonly used nonlinear optical material, while α-BBO has actually been much less researched.

α-BBO is a suitable UV birefringent crystal with facility symmetry and non-linear result, yet it has an excellent birefringence index, specifically in the ultraviolet band with a high transmission proportion (95%), passage variety of 189nm ~ 35000nm, steady physical and also chemical residential or commercial properties, superb mechanical properties.


α-BBO crystals have exceptional optical residential or commercial properties such as huge refractive index as well as vast passage variety and are widely utilized in optical deflection technology, high power laser, and also ultrafast laser applications. It is generally utilized to make ultraviolet polarization prisms such as the Grantler prism, Wollaston prism, high power optical isolator as well as group speed inequality compensator of the ultrafast laser.


BBO is a typical nonlinear optical crystal. Nonlinear optical crystal is a sort of crystalline material which uses the nonlinear action of light wave polarization when it travels through the tool to react on the light wave, resulting in harmonic generation (nonlinear effect) at the sum regularity, distinction frequency, and so forth. BBO crystal is acknowledged as one of the superb 2nd-order nonlinear optical crystals worldwide.

Nonlinear property

Nonlinear optical crystals are those that show more than quadratic nonlinear optical effects to laser intense electrical field. Nonlinear optical crystal is a type of useful product, in which regularity doubling (or “frequency conversion”) crystal can be used to convert laser wavelength, so regarding extending the tunable range of laser, which has crucial application value in laser modern technology area.


  • 1) Utilized in 1064nm Nd: YAG laser with a dual, three-way, quadruple, and quad regularity.
Regularity doubling

The laser frequency doubling strategy significantly increases the laser band as well as is the main method to transform the laser to the short wavelength instructions. Laser regularity doubling is extensively used in laser innovation. In order to obtain the laser with a shorter wavelength, it can increase the regularity of multiple stages. Presently, it has actually gotten to the functional level, as well as there are industrial gadgets and gadgets, which have an extremely wide range of applications.

BBO crystal
BBO crystal

Interpretation: An effect that makes use of a nonlinear product to accomplish a laser regularity twice the frequency of the input light

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Regularity doubling is a usual method used to produce short-wavelength light:

By increasing the frequency of a 1064nm laser outcome utilizing neodymium-doped or ytterbium-doped laser to generate 532nm green light.

Lots of blue laser systems use 0.9 um laser (such as Nd: YVO4 produced by 914nm) with frequency increasing.

By additional doubling the regularity (or by the summing result), lasers can be produced in the ultraviolet region at also much shorter wavelengths (see ultraviolet lasers). The major obstacles are the transparency, resilience, and also strong dispersion of nonlinear crystalline products in this area (often resulting in tough phase matching or extremely slim phase matching data transfer).

  • 2) Used for color laser as well as titanium gem laser of double frequency, triple frequency, amount regularity, difference frequency, etc
  • 3) Optical Parametric Amplifier (OPA) and also Optical Parametric Oscillator (OPO).

optical parametric boosting as well as oscillation refers to the nonlinear optical effects generated by multiwave blending. Optical parametric amplification and also oscillation are both second-order nonlinear optical blending procedures. Optical parametric amplification as well as the oscillation of three-wave mixing have been studied most and have actually been widely made use of in the generation of tunable lasers.

Electro-optical properties.

Along with the superb nonlinear effect, another noticeable optical building of BBO is the electro-optical result.

The electro-optic effect is a general term for the modifications of optical buildings of objects under the activity of the used electric field. Usually, this used electrical area changes extremely slowly with time compared to the regularity of light. These various electro-optical effects fall into 2 groups:

Modifications in light absorption

Electroabsorption effect: A variant of light absorption constant in the general sense.

Franz-caldisi effect: Change in light absorption of certain big semiconductors under a used electric field.

Quantum confinement Stark effect: Variation of light absorption in specific semiconductor quantum Wells under an applied electric area.

Electric color result: The absorption of a certain wavelength by a used electrical area, resulting in a change in the shade of things.

Modifications in refractive index as well as dielectric consistency.

Pockers effect (also called straight electro-optic impact): The modification of the refractive index of the crystal caused by a used electric field is proportional to the intensity of the electrical area. Only those crystals without inversion proportion can create the Pockers effect.

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Kerr effect (likewise known as a second-order nonlinear electro-optical result): The adjustment of the refractive index of the crystal brought on by a used electrical field is symmetrical to the square of the electrical area intensity. Any kind of crystal can produce the Kerr impact, but the toughness of the effect is a lot lower than that of the Pockers impact.


BBO Electro-optic Q-Switch (Pockels cell).
Pockels cell
Pockels cell

Compared to conventional KD * P electro-optic modulated crystal, BBO( barium metaborate β-BaB2O4) crystal has an extremely low absorption coefficient. There are likewise weak piezoelectric ringing effects, a broader spectrum transmission range (210-2000nm) as well as other advantages. Compared with RTP electro-optic modulated crystal, BBO crystal has a greater termination ratio, anti-damage threshold, and temperature level flexibility, which contributes to boosting the stability of laser outcome power.

As a result, the electro-optical Q button made of BBO crystal is commonly made use of in the electro-optical Q-switched solid-state laser with high rep frequency (1MHz) and also high power (approximately 1000W), cavity inversion air-conditioned Q laser as well as all-solid picosecond and also femtosecond regeneration amplification laser system. BBO electro-optical Q button can be switched off and also stand up to up to 150W of oscillating optical power in the cavity (laser outcome power up to 50W) without water air conditioning.

The disadvantages of BBO crystals are the small electro-optic coefficient and reasonably high half-wave voltage, so the half-wave voltage, as well as quarter-wave voltage, can be lowered by raising the length of the crystal as well as using 2 BBO crystals in the collection.


As a result of the low reliability of BBO, the surface area of refined BBO crystals is quickly blurred by wet air. So after the polishing procedure, a slim film finish is put on the surface. The safety finishing (P coating) or anti-reflective covering (AR finishing) safeguards the crystal surface area from dampness somewhat. Nonetheless, also tiny pollutants (dust particles, strain, fingerprints, and so on) can impact the performance of BBO crystals, i.e. transmission or reflection. On top of that, BBO crystals are quickly harmed if contaminants enter direct contact with laser radiation.

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