BBO crystal properties

Barium borate is an inorganic substance with the chemical formula BaB2O4. It can exist as a hydrate, a dried form, a white powder, or an anemic crystal. There are two different kinds of heat phase (α-BBO) as well as a reduced temperature phase (β-BBO), and the phase transition temperature level is 925 °C.

1. α-BBO

β-BBO crystal growth has actually been researched for more than two decades and has also come to be an extremely commonly used nonlinear optical product, while α-BBO has been less researched. α-BBO is a perfect UV birefringent crystal with a high transmission ratio (95%), a transmittance range of 189 nm–35000 nm, stable physical and chemical properties, and excellent mechanical properties.


α-BBO crystals are widely used in optical deflection technology, high power laser, and ultrafast laser applications due to their exceptional optical residential or commercial properties, such as a large refractive index and wide passage variety. It is primarily utilized to make ultraviolet polarization prisms such as the Grantler prism and the Wollaston prism, a high-power optical isolator, and also a group speed inequality compensator for ultrafast lasers.

2. β-BBO

BBO nonlinear crystal is an usual nonlinear optical crystal. Nonlinear optical crystals are crystalline products that use nonlinear feedback of light wave polarization when they pass through a tool to respond to the light wave, causing harmonic generation (nonlinear effect) at the amount of regularity, distinction regularity, and so on. BBO crystal is recognized as one of the best second-order nonlinear optical crystals on the planet.

Nonlinear property of BBO

Nonlinear optical crystals are those that show more than quadratic nonlinear optical impacts in the laser’s extreme electrical field. The nonlinear optical crystals are a type of useful material in which a frequency doubling (or “frequency conversion”) crystal can be used to transform laser wavelength in order to extend the tunable range of a laser, which has critical application value in the field of laser modern technology.


1) Utilized in 1064nm Nd: YAG laser with dual, triple, quadruple as well as quad frequency.

Frequency doubling

The laser regularity increasing method considerably increases the laser band and is also the main method for transforming the laser to the short wavelength direction. Laser regularity-increasing is a common technique in laser innovation. It is possible to increase the frequency several steps in order to obtain a laser with a much shorter wavelength. It has now progressed to the functional level, with business tools and gadgets that have an extremely broad range of applications.

Definition: An effect that utilizes a nonlinear product to achieve a laser frequency twice the frequency of the input light.

Regularity increasing is a typical strategy used to generate short wavelength light:

  • By increasing the regularity of a 1064 nm laser output using neodymium doped or ytterbium-doped laser to generate 532nm green light.
  • Numerous blue laser systems make use of 0.9 um laser (such as Nd: YVO4 produced by 914nm) frequency increasing.

Lasers in the ultraviolet region at shorter wavelengths can be created by doubling the regularity (or by the summing effect) (see ultraviolet lasers). Transparency, toughness, and solid diffusion of nonlinear crystalline products in this region are the main challenges (in some cases leading to difficult phase matching or extremely slim stage matching data transfer).

2) Used for color laser and also titanium treasure laser of double regularity, triple regularity, amount regularity, distinction frequency, and so on.
3) Optical Parametric Amplifier (OPA) as well as Optical Parametric Oscillator (OPO).

Optical parametric boosting and oscillation describe the nonlinear optical impacts generated by multiwave mixing. OPA and OPO are both second-order nonlinear optical mixing processes. Optical parametric boosting and oscillation of three-wave mixing have received the most attention and are widely used in the development of tunable lasers.

Electro-optical properties of BBO

In addition to the outstanding nonlinear result, one more popular optical residential or commercial property of BBO is the electro-optical effect.

The term “electro-optic effect” refers to the changes in the optical residential or commercial properties of objects caused by an electric field. Usually, this electrical area changes extremely gradually with time, compared to the frequency of light. These various electro-optical results fall into two categories:

Changes in light absorption

Electroabsorption effect: variation of light absorption as a whole.

  • The Franz-Caldisi effect: a change in the light absorption of specific large semiconductors in the presence of an applied electric field.
  • Quantum arrest stark effect: variation of light absorption in certain semiconductor quantum wells under a used electrical field.
  • Electric color effect: The absorption of a details wavelength by an applied electric area, causing a modification in the shade of an item.

Modifications in refractive index and also dielectric continuity

Pockels effect (also known as linear electro-optic effect): The change in refractive index caused by an electric field is proportional to the strength of the electric field. Only crystals without inversion symmetry can produce the Pockels effect.

Kerr effect (also known as second-order nonlinear electro-optical effect): The change in refractive index of the crystal brought on by an electric field is proportional to the square of the electrical area strength. Any crystal can create the Kerr effect, but the toughness of the effect is much lower than that of the Pockers impact.


BBO Electro-optic Q Switch (Pockels cell)

BBO (barium metabate, BaB2O4) crystal has a much lower absorption coefficient than traditional KD*P electro-optic modulated crystal. There are likewise weak piezoelectric buzzing effects, a larger spectrum transmission array (210–2000 nm), as well as other benefits. When compared to RTP electro-optic regulated crystal, BBO crystal has a higher extinction proportion, anti-damage threshold, and temperature adaptability, all of which contribute to improved laser output power stability.

As a result, electro-optical Q buttons made of BBO crystal are frequently used in electro-optical Q-switched solid-state lasers with high repetition rate (1 MHz) and high power (approximately 1000 W), cavity inversion cool Q lasers, and all-solid picosecond and femtosecond regrowth boosting laser systems. The BBO electro-optical Q switch can be switched off and also stand up to approximately 150 W of oscillating optical power in the tooth cavity (laser output power of as much as 50 W) without water cooling. The drawbacks of BBO crystal are a small electro-optic coefficient and also a fairly high half-wave voltage, so the half-wave voltage as well as the quarter-wave voltage can be minimized by enhancing the size of the crystal and using two BBO crystals in series.

Preventative measures

Due to the reduced deliquability of BBO, the surface of sleek BBO crystals is conveniently obscured by wet air. So, after the brightening process, the surface is given a thin film finish. The safety coating (P coating) or anti-reflective layer (AR coating) safeguards the crystal surface from moisture to some extent. Nevertheless, even tiny impurities (dirt fragments, pressure, finger prints, and so on) can influence the performance of BBO crystals, i.e., transmission or reflection. Furthermore, BBO crystals are conveniently harmed if pollutants enter direct contact with laser radiation.

Read more: Crystal commonly used in lasers

By Nikitha

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