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BBO – Barium borate

>0.5 J/cm2 @ 213 nm, 10 ns, 10 Hz | 190 nm - 2200 nm

Barium-borate (BBO or BaB2O4) has two phases:

α phase – high temperature phase

β phase – low temperature phase

 

β-barium-borate (BBO) differs from the α-barium-borate by the positions of the barium ions in the crystal.

Although both α-BBO and β-BBO phases are birefringent, α-BBO phase has centric symmetry and thus  different nonlinear properties in comparison to the β-BBO phase.

Beta-barium-borate (BBO) is a non-linear optical (NLO) crystal with a set of specific features: large non-linear coefficient for ultraviolet (UV), high damage threshold, broad phase matching, low GDD for ultrafast applications and wide transparency range.

BBO crystals are one of the best electro-optical (E-O) crystals and TOP tier non-linear optical (NLO) crystals, they are widely used for 2nd – 5th harmonic generations in most popular lasers and optical parametric oscillators (OPO), mostly (but not limited to) Ti:Sapphire, Yb:KGW/KYW laser systems, pockel cells and other applications.

Formule
  • Advantages and Features
  • Available thin film coatings
  • Applications
  • Tips
  • Broad phase matching range for harmonics generation down to 200 nm;
  • Broad transparency ranges from 190 nm to 2200 nm;
  • High damage threshold;
  • Low thermo-optical dependence of phase matching makes BBO the most stable crystal for high power applications;
  • Relatively high non-linear coefficients for UV-VIS applications;
  • Small angle tuning range makes it most attractive for OPA/OPO wide wavelengths region generations;
  • Broad band anti-reflective (AR) coatings for OPA/OPO applications;

BBO crystal has moderate hygroscopic properties, thus thin film coating is extremely recommended to prevent crystal form absorbing moisture from air.

  • Protective coating (P-coating) can be used to protect surfaces
  • If low reflection is required 3photon offers anti reflective (AR) coatings:
    • Single Layer of MgF2 or similar dielectric material – for optimal pricing;
    • Single wavelength or single band (V-coating) – optimized for your working wavelength;
    • Two band coating (W-coating) – optimized for two wavelengths;
    • Multi-wavelength – optimized for 3 or more wavelengths;
    • Broadband (BBAR coating) – for universal applications;
    • Narrow band (NBAR coating) – for your R&D projects.

Nd:YAG Laser Systems Harmonics:

BBO is one of the best crystals for picosecond SHG (532 nm), THG (355 nm) generation or with any pulse duration for 4th (266 nm) or 5th harmonic generation (213 nm).

Ti:Sapphire Laser Systems Harmonics:

BBO is the best crystal for ultrashort SHG (400 nm), THG (266 nm), 4th (200 nm) generation.

OPO/OPA Applications:
BBO OPO/OPA pumped:
355 nm for 400-2400 nm generation
532 nm for 650-2400 nm generation
800 nm for 1200-2400 nm generation.

Type 2 BBO used for further Double-Frequency-Generation (DFG) mixing of signal and Idler
Non-collinear BBO OPA pumped @ 400 nm for pulses with wide spectral width generation in order to obtain ultrashort <4 fs pulses.

Electro-optical (E-O) applications:

Due to electro-optical properties the BBO crystal best suits for use for fast Pockels Cells production.

As Birefringent material applications:

BBO crystal is widely used for temporal walk-off compensation to synchronize the different wavelength pulses after harmonic or other optical setup stages. Could be used for compensation of very short femtosecond to picosecond pulse temporal differences.
Due high spatial walk-off, the BBO crystal could be used for different polarization beams separation in space. This could be used for custom prism or polarizers production.

BBO crystal transporting, handling, inspecting, storing and cleaning tips

BBO crystals are somewhat moderately hygroscopic, so after the polishing procedure the thin film coatings are applied. Protective coating (P-coating) or anti-reflective coating (AR coating) protects the crystal surface from humidity to some extent. However even very small pollutants (dust particles, strains, fingerprints, etc.) can affect the performance of BBO crystal, i.e. transmission or reflection. Furthermore, if pollutant is in direct contact with laser radiation, BBO crystal will be easily damaged.

 

Transporting
3photon BBO crystals are packed in plastic transparent membrane boxes which are put in vacuumed plastic bags in order to protect the crystal – prevent mechanical shock and exposure to humidity.
Mounts (holders) for BBO crystals with complex dimensions (thin or small crystals) can also be provided by 3photon.

Handling
Avoid touching BBO crystals with your bare hands! 3photon recommends using forceps or plastic tweezers to hold optical components, if that is not possible, please wear powder-free gloves or finger cots instead.

Inspecting
Open the BBO crystal membrane box only in clean environment, 3photon suggest inspecting BBO crystals in clean room or at least in controlled environment with relative humidity of 20%-30% or less.
Keep crystal’s temperature equal to inspection room temperature, because the temperature difference allows water vapor condensation thus reducing the performance and lifetime of BBO crystal.

Storing
It is necessary to store the BBO crystal in a clean and dry place.
If you are planning to store crystal for more than 1-2 weeks:
• Place the crystal in a clean and dry place;
• Avoid using the same plastic membrane box to store BBO crystal;
• 3photon recommends using a desiccator for storage.

Cleaning
Never use acetone for cleaning, it will damage BBO crystal.
Never breath-blow to remove pollutants, due to hygroscopic properties BBO crystal can be damaged.
Drop and drag method:
A. Silk tissue and Mixture (High purity alcohol and ether mixed with ratio 1:1 (50%-50%))
B. Lens tissue

The principle of procedure:
1. Take clean tissue and pace it on the surface you intend to clean
2. Drip small drop of:
2.1. (A) Mixture on tissue
2.2. (B) Pure-Isopropyl-Alcohol (IPA) on tissue
3. Drag the tissue in single direction through the surface;
4. In case of Lens tissue – do not use the same tissue repeatedly.
Be extremely careful while cleaning thin and/or small BBO crystals, the material is soft and can be easily damaged

Gas blowing method

Dust particles and pollutants can also be removed by blowing either Nitrogen (N2) or clean air into the BBO crystal, 3photon strongly recommends maintaining humidity (moisture) as low as possible.

Be extremely careful while blowing thin and/or small BBO crystals, 3photon recommend keeping approximately 10-20 cm distance from BBO crystal while cleaning with gas blowing method, otherwise BBO crystal can be easily blown off.

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