Beta BBO Pockels Cells or beta barium borate pockels cells exhibit significant advantages over other materials in terms of laser power handling abilities, temperature endurance, and substantial freedom from piezoelectric ringing. Beta BBO Pockels cells 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. BBO pockels cells are a better option than KDP pockels cells in the field of high repetition rate and high power applications. On account of the low piezoelectric coupling coefficients of the top-notch-quality BBO crystals that we incorporate into our Pockels Cells, our BBO Pockels cells are capable of generating pulses with repetition rates of hundreds of kilohertz.

Shanghai North Optics offers off-the-shelf and custom BBO Pockels Cells with high damage threshold, low insertion loss, high extinction ratio, minimal piezoelectric ringing, and competitive price. BBO Pockels Cells with both Single and double BBO crystal designs and low-voltage geometries are available upon request. Besides, we also offer BBO crystals for EO applications.

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Features:

• BBO Pockels cells 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 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 have a wide transmission range of 189nm to 3500nm, which allows them to be used in diverse applications from UV to NIR spectrum. 

•  Low Absorption and absence of piezoelectric ringing:

Compared to LiNbo3, BBO crystals are much less impaired by piezoelectric when voltage is applied. The other important feature of BBO electro-optics is their 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 relatively small electro-optic coefficient, and hence a high operation voltage. North Optics offers customized BBO crystals with the required dimensions as well. Our panel of engineers could offer professional consultancy and help you ascertain the optimized solution for your needs.

 Cautions:

• BBO crystals are hygroscopic and therefore it is recommended to preserve and use them in a 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.
• Shanghai North Optics engineers can offer you a suitable and high-quality Pockels Cell 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.

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-transmitting nonlinear crystals
• High laser-induced damage threshold (LIDT)
• Wide transmittance range from 188 nm to 5.2μm (appropriate transmission @3μm-5.2μm, tens of μm thick crystal)
• Extremely low capacitance (1< pF) which permits 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 smaller 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

                                                                                                                                     Fig.2 Transparency Curve of BBO crystal

Application Notes:

When it comes to practical applications of Pockels cells, one might need to take some additional side effects into account:

• Etalon effects might still exist and affect the optical performance if the beam direction is perpendicular to the faces of the crystal, Even when the end faces of the crystal are coated with high-quality AR coatings.
• The temperature could significantly affect the obtained phase changes. For example, a Pockels cell set to generate perfect high-contrast amplitude modulation might require readjustments of the operation voltages when the temperature changes. However, there are thermally compensated double-crystal designs that might circumvent the problem.
• For an operation with a large beam radius, it is worth paying attention to sort out an optimized design for electrodes (possibly with additional auxiliary electrodes for high uniformity of the generated electric field, as otherwise one may obtain a spatially varying modulation).
• Nonlinear crystals often exhibit substantial piezo-electric and electrooptic effects, which can have substantial influences on the performance at high modulation frequencies.
• Operating at high power levels, thermal effects may be induced by residual absorption of the crystal. Therefore materials with lower absorption are preferable for high-power applications
• The crystals used in Pockels cells are nonlinear crystal materials, they inherently demonstrate considerable optical nonlinearities. For instance, self-phase modulation and nonlinear self-focusing might occur for light pulses with substantial peak power.

Calculation of Quarter-wave Voltage

The voltage required to produce a retardance of π radians is called the halfwave voltage or simply Vπ. For an optical input linearly polarized 45o applying a halfwave voltage rotates the polarization by 90o. When the output wave is passed through a linear the resultant can be rapidly modulated from maximum intensity to minimum intensity by rapidly changing the voltage applied to the crystal from 0 volts to Vπ.

The halfwave voltage of BBO is dependent on the optical wavelength and is given by:

Where   λ=optical wavelength 
         d=electrode spacing 
         L=optical path length 
         r22=electro-optic coefficients 
         no=ordinary indices of refraction

EO Q-Switch 1/4Wave Voltage Vs wavelength (3x3x20mm) 
1/4 Wave Voltage @1030nm : Vπ/2 =3388V

Pockels Cell Comparison Chart: