BBO Crystals for EO Applications

Beta BBO crystals or beta barium borate crystals exhibit significant advantages over other materials in terms of laser power handling abilities,high damage threshold temperature stability, and substantial freedom from piezoelectric ringing. Beta BBO crystals are the most attractive candidates for high repetition rate Q-switching, pulse picking at up to 3 MHz, laser cavity dumping, regenerative amplifier control and beam chopper.Beta-Barium Borate ( BBO) crystal is an excellent electro-optic crystal for high power applications at the wavelength range from 200nm to 2,500nm. Hangzhou Shalom EO offers BBO crystals used in the pockels cells with high precision polishing, AR coating and Cr-Au electrodes and competitive price. Stocked crystals of standard specifications is ready for selecting, and the customized special crystals is available upon customer's request. Besides, we also offer BBO pockel cells.Click Here to visit our archives to learn more about pockels cells.

Physical properties of BBO:

Crystalline structure	Trigonal, space group R3c, Point group 3m	Cell Parameters	a = b = 12.532 Å, c = 12.717Å, Z = 6
Melting point	1095±5℃	Phase transition point	925±5℃
Optical Homogeneity	δn ~ 10-6 /cm	Mohs hardness	4
Density	3.85 g/cm3	Specific heat	1.91J/cm3 xK
Hydroscopicity	Low	Thermal expansion coefficients	a,4 x 10-6/K;c, 36x 10-6/K
Thermal Conductivity	⊥c,1.2W/m/K; //c, 1.6W/m/K	Absorption Coefficient	< 0.1% /cm (at 1064 nm)

Optical properties of BBO:

Transparency Range	189-3500 nm	Refractive Indices at 1064 nm at 800 nm at 532 nm at 400 nm at 266 nm	no = 1.6545, ne = 1.5392 no = 1.6606, ne = 1.5444 no = 1.6742, ne = 1.5547 no = 1.6930, ne = 1.5679 no = 1.7585, ne = 1.6126
Thermo-optic Coefficients	dno/dT = -9.3 x 10-6 /°C dne/dT = -16.6 x 10-6 /°C	Electro-optic Coefficients	γ11 = 2.7 pm/V, γ22, γ31 < 0.1 γ11
Effective Nonlinearity Expressions	dooe= d31 sinθ +(d11 cos3φ - d22 sin3φ) cosθ deoe= (d11 sin3φ + d22 cos3φ) cos2θ	Half-wave Voltage	48 kV (at 1064 nm)
NLO Coefficients	d11 = 5.8 x d36(KDP) d31 = 0.05 x d11 d22 < 0.05 x d11	Damage Threshold (Bulk) at 1064 nm at 532 nm	5 GW/cm2 (10 ns); 10 GW/cm2 (1.3 ns) 1 GW/cm2 (10 ns); 7 GW/cm2 (250 ps)
Phase-matchable SH Wavelengths:	189 - 1750 nm

  

                        Fig.1  Transparency Curve of BBO 

• They are the best choice for high repetition rate Q-switching:

Because it relies on the electro-optical effect, switching time - aided by the low capacitance of the Electro-Optical Q Switch is very fast, therefore it has surpassing performance for high repetition rate lasers up to 1MHz. All-solid-state short-cavity Q-switched laser using BBO electro-optic Q-switch can generate high-energy laser with a pulse width of less than 4ns.

•  High damage threshold and power handling capability:

Without water cooling, the BBO electro-optical Q switch can be turned off and withstand up to 150W intracavity oscillation optical power (laser output power up to 50W).

•  Wide Transmission range from UV to NIR:

BBO crystals has a wide transparency range of 189nm to 3500nm, which allows it to be used in diverse applications from UV to NIR spectrum. 

•  Low Absortion and piezoelectric ringing:

Comparing to LiNbo3, BBO crystals are much less impaired by piezoelectric when voltage is applied. The other important feature of BBO electro-optics is their very low absorption and associated laser-induced thermal birefringence. Due to the low absorption, very little optical heating will occur at operating wavelengths in the visible and near IR.

• Relatively high half wave voltage:

BBO has a comparatively small electro-optic coefficient, and hence high applying voltage.Shalom EO offers customized BBO crystals with required dimensions as well. Our panel of engineers could offer professional consultancy and help you ascertain the optimized solution for your need.

Features of BBO crystal：

• Ultra-thin crystals can be used for ultra-fast (<10 fs) applications
• Wide phase matching range of various second-order nonlinear interactions in almost the entire transparent range
• The highest nonlinearity among all UV nonlinear crystals
• High laser induced damage threshold (LIDT)
• Wide transmittance range from 188 nm to 5.2μm (appropriate transparency @3μm-5.2μm, tens of μm thick crystal)
• Extremely low capacitance (1< pF) will permit high repetition rate switching with rise times on the order of 100 ps or less
• High damage threshold capable of withstanding high peak power intensities of samller beam size and therefore suitable for compact design ( However, small crystal aperture leads to diffraction losses and hence might increase the insertion losses.)
• Not prone to piezo-electric ringing
• Low absorption and associated laser-induced thermal birefringence
• High extinction ratio

Applications:

1. High repetition rate DPSS Q-switches
2. High repetition rate regenerative amplifier control
3. Cavity dumping and Beam chopper
4. Low dispersion suitable for short pulse regenerative amplifiers

          

Fig.1  Qualitative comparison of acoustic ringing in BBO and LiNbO3 

                                   The intensity transmitted through the LiNbO3 Pockels cell varies greatly due to piezoelectric effects, whereas the light transmitted through

                                   the BBO Pockels cell follows the decay of the applied high voltage pulse with no evident acoustic ringing

Cautions:

• BBO crystals are hydroscopic and therefore it is recommended to preserve and use them in dry environment.
• Precautions need to be taken to protect its polished surfaces since BBO is comparatively vulnerable.
• The acceptance angle of BBO is small, so be careful when it comes to adjusting angles.
• Hangzhou Shalom EO engineers can offer you the best suitable and high quality crystal according to the characteristics of your lasers. The parameters we take into concern include pulse width , energy per pulse, repetition rate for a pulsed laser, power for a cw laser, divergence, laser beam diameter, wavelength tuning range, mode condition, etc.

Tags: Getting to know BBO Crystals for EO Applications

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