Home > NLO Crystals >> Pockels Cells

Pockels Cells, E-O Modulators, Q-switches

The Pockels effect was first described in 1906 by the German physicist Friedrich Pockels. It is the linear electro-optic effect, where the refractive index of a medium is modified in proportion to the applied electric field strength. This effect can occur only in non-centrosymmetric materials. The most important materials of this type are crystal materials such as lithium niobate (LiNbO3), lithium tantalate (LiTaO3), potassium di-deuterium phosphate (KD*P), β-barium borate (BBO), potassium titanium oxide phosphate (KTP), compound semiconductors such as gallium arsenide (GaAs) and indium phosphide (InP). And a relatively new development poled polymers, which containing specifically designed organic molecules. Some of these polymers exhibit a huge nonlinearity, with nonlinear coefficients which are an order of magnitude larger than those of highly nonlinear crystals.

1. BBO crystal

BBO is an excelent electro-optic crystal for high average power Pockels cell applications at the wavelength range from 200nm to 2500nm. BBO has a high damage threshold and a low dielectric constant and is useful in high repetetion rate, high average power (up to 150W) diode pumped solid state lasers (DPSS lasers). BBO has significant advantages over other materials in terms of laser power handling abilities, temperature stability, and substantial freedom from piezoelectric ringing. The capacitance of BBO crystal is lower than other E-O crystals which make the Pockels cell response very fast.

features

- high damage threshold, 150 W CW with water cool, 5GW/cm² @1064 nm 10 ns
- no piezoelectric ringing for frequency up to 30 kHz
- broad trasmission range from 200 nm to 2000 nm
- high temperature stability
- half-wave voltage 9.3KV 4x4x20 mm @1064 nm
- high repetition rate DPSS Q-switch
- high repetition rate regenerative amplifier control
- cavity dumping
- beam chopper

2. KTP (KTiOPO4) crystal

KTP has promising E-O and dielectric properties comparing to other E-O crystals. The following table gives the comparison of KTP and those commonly used E-O modulator materials:

Combining these properties with high damage threshold, low optical loss at high average power, wide optical bandwidth, thermal and mechanical stability, KTP crystals are expected to replace LiNbO3 crystals as E-O modulators, especially for mode-locking diode laser pumped Nd:YAG and Nd:YLF lasers as well as Ti:Sapphire and Cr:LiSrAlF6 lasers.

Features

- high-polarization-extinction ratio
- low dynamic half-wave voltage
- free from acoustic ringing
- damage threshold 500 MW/cm² @1064 nm 10 ns
- wide optical bandwidth (>15 GHz)
- transmission 400 nm to 2500 nm
- half-wave voltage 1.3 KV 4x4x20 mm @1064 nm
- high repetition rate regenerative amplifiers
- E-O modulators

3. LiNbO3 crystal

LiNbO₃ is widely used as electro-optic modulator and Q-switch for Nd:YAG, Nd:YLF and Ti:Sapphire lasers as well as modulator for fiber optics, etc. The transverse modulation is mostly employed for LiNbO3 crystal. If the light propagates in z-axis and electric field applies to y-axis, the refractive retardation will be:

φ = πLnγ₂₂/(λd); where L is crystal length, d is width.

If the light propagates in y-axis and electric field applies to z-axis, the refractive retardation will be:

φ = πLnγ₃₃/(λd); where L is crystal length, d is width.

The electro-optic coefficients of LiNbO3 are:

γ₃₃ = 32 pm/V, γ₃₁ = 10 pm/V, γ₂₂ = 6.8 pm/V at low frequency

γ₃₃ = 31 pm/V, γ₃₁ = 8.6 pm/V, γ₂₂ = 3.4 pm/V at high electric frequency.

MgO:LiNbO3 and ZnO:LiNbO3 crystals have similar electro-optic properties as LiNbO3 but with higher damage threshold.

LiNbO3 and MgO:LiNbO3 are also used for acousto-optic modulation. The refractive index of an optical medium is altered by the presence of sound, this is called acousto-optic effect which can be used in many devices include optical modulators, switches, deflectors, filters, frequency shifters and spectrum analyzers. OptoCity provides several kinds of acousto-optic crystals: LiNbO3 SAW wafers, LiTaO3 SAW wafers, TeO2 and PbMnO4 crystals.

Features

- non-hygroscopic
- damage threshold 300MW/cm² @1064 nm 10 ns
- half-wave voltage 1.7 KV 4x4x20 mm @1064 nm
- transmission 400 nm to 4000 nm
- because piezoelectric ringing can be severe, piezoelectrically damped designs can be very helpful.
- optical modulation and Q-switching of infrared wavelengths

4. DKDP crystal

DKDP was the most commonly used E-O crystal for ns laser Q-switch.

Features

- economically priced
- large aperture available
- transmission from 400 nm to 1100 nm
- damage threshold: 1 GW/cm² @1064 nm 10 ns
- half-wave voltage 6 KV @1064 nm, longitudinal mode
- Q-switching of the laser cavity
- cavity dumping

5. RTP

RTP is a newly developed E-O crystal. Its property is similar to that of KTP crystal but has higher damage threshold.

Features

- no piezoelectric ringing and hotorefractive damage at high peak power for frequency up to 100 kHz
- thermal compensating design
- high damage threshold 1 GW/cm² @1064 nm 10 ns
- non-hygroscopic
- transmission 400 nm to 2500 nm
- half-wave voltage 1.8 KV 4x4x20 mm @1064 nm
- Q-switch at high repetition rates, high-peak-power laser

General Specifications

Optocity offer standard and custom made E-O crystals for applications of Q-switch, phase & amplitude modulations. Please contact our sales for details.

Request E-O Crystals for Quote