BBO – Barium borate

• The broad phase-matching range for harmonic generation is down to 200 nm
• Broad transparency ranges from 190 nm to 2200 nm
• High damage threshold: >10 J/cm² @ 266 nm, 10 ns, 10 Hz
• Low thermo-optical dependence of phase matching makes BBO the most stable crystal for high-power applications
• Relatively high nonlinear coefficients for UV-VIS applications
• The small angle tuning range makes it highly attractive for OPA/OPO wide wavelength region generation
• Broadband anti-reflective (AR) coatings for OPA/OPO applications

BBO crystal has moderate hygroscopic properties, so thin film coating is highly recommended to prevent the crystal from absorbing moisture from the air.

• A protective coating (P-coating) can be applied to protect surfaces
• If low reflection is required, 3photon offers IBS anti-reflective (AR) coatings in the following options:
  • Single layer with the highest LIDT – 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 three or more wavelengths;
  • Broadband (BBAR coating) – for universal applications;
  • Narrowband (NBAR coating) – ideal for R&D projects.

Nd:YAG Laser Systems Harmonics:

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

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 is used for further Double-Frequency-Generation (DFG) mixing of signal and idler.
Non-collinear BBO OPA, pumped at 400 nm, generates pulses with wide spectral width to achieve ultrashort pulses of <4 fs.

Electro-optical (E-O) applications:

Due to its electro-optical properties, the BBO crystal is ideal for fast Pockels cell production.

As a Birefringent Material:

The BBO crystal is widely used for temporal walk-off compensation, synchronizing different wavelength pulses after harmonic or other optical setup stages. It can also be used to compensate for temporal differences in very short pulses, ranging from femtoseconds to picoseconds.
Due to its high spatial walk-off, the BBO crystal can separate beams of different polarizations spatially, which makes it suitable for custom prism or polarizer production.

BBO Crystal Transport, Handling, Inspection, Storage, and Cleaning Guidelines

BBO crystals are moderately hygroscopic, which is why thin film coatings are applied after polishing. Protective coatings (P-coating) or anti-reflective coatings (AR coating) provide some protection against humidity. However, even the smallest contaminants (dust particles, stains, fingerprints) can degrade the crystal’s performance, impacting transmission or reflection. Additionally, if contaminants come into direct contact with laser radiation, the BBO crystal is susceptible to damage.

Transporting
3photon BBO crystals are packaged in transparent membrane boxes and vacuum-sealed plastic bags to safeguard them from mechanical shock and humidity. For BBO crystals with complex dimensions (such as thin or small crystals), custom mounts or holders can also be supplied by 3photon.

Handling
Never handle BBO crystals with bare hands! 3photon advises using forceps or plastic tweezers for handling optical components. If these are not available, ensure you wear powder-free gloves or finger cots.

Inspecting
Open the BBO crystal’s membrane box only in a clean environment. 3photon recommends inspecting BBO crystals in a clean room, or at the very least in a controlled environment with relative humidity between 20% and 30%. Ensure the crystal’s temperature is equal to the inspection room’s temperature, as any difference can cause condensation, compromising the crystal’s performance and lifespan.

Storing
Store the BBO crystal in a clean, dry environment. For storage periods exceeding 1-2 weeks:
• Ensure the crystal is placed in a clean and dry space
• Avoid reusing the original plastic membrane box for extended storage
• 3photon recommends using a desiccator for optimal storage conditions

Cleaning
Never use acetone to clean the BBO crystal, as it will cause damage.
Also, avoid using breath to remove contaminants, as the crystal’s hygroscopic properties could result in damage.
Drop and drag method:
A. Silk tissue with a mixture of high-purity alcohol and ether in a 1:1 ratio (50%-50%)
B. Lens tissue

Cleaning procedure:
1. Place a clean tissue on the surface to be cleaned
2. Apply a small drop of:
2.1. (A) Mixture to the tissue
2.2. (B) Pure Isopropyl Alcohol (IPA) to the tissue
3. Drag the tissue in a single, continuous direction across the surface
4. When using lens tissue, avoid reusing it
Exercise extreme caution when cleaning thin or small BBO crystals, as the material is delicate and easily damaged.

Gas-blowing method

Dust and contaminants can be removed by blowing nitrogen (N2) or clean air onto the BBO crystal.

3photon strongly advises keeping humidity as low as possible during this process. When using the gas-blowing method on thin or small BBO crystals, maintain a distance of 10-20 cm to prevent accidentally dislodging or damaging the crystal.