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Electro Optical Components, Inc. Transverse Field Pockels Cells

Description
Unlike the EM500 range of Pockels cells, the transverse field Pockels cells can be made in a more flexible range of sizes and in a greater choice of materials. The construction usually consists of either one Z-cut crystal in the case of lithium niobate, or two X or Y cut crystals, orientated for birefringence cancellation in the case of lithium tantalite. Other materials are available to suit special requirements, but none can match these for their established quality and low cost. For most applications, the designs can be mounted in a simple machined aluminum alloy channel housing of an appropriate size to match the crystal(s). If necessary, this may incorporate special fixing or other dimensional requirements at a moderate cost. Lithium Niobate (LiNbO3) Lithium Niobate (LiNbO3) is a very important material for transverse Pockels cell manufacture. It possesses excellent transparency over a wide spectral range of 450nm to just over 4μm. Optical damage can be a problem at short wavelengths because of color center formation. Above 800nm, however, this effectively disappears and the material then has a very good optical damage resistance. This makes it very suitable for Q-switching compact Nd+ lasers such as found in laser rangefinders. There are two orientations which may be used successfully for lithium niobate electro-optic devices and the choice is usually determined by the application. The first and the simplest involves using a z-cut bar where the optical axis of the material is parallel to the direction of optical propagation so there is no birefringence encountered. This simplifies the design of the optical system as good thermal stability is ensured automatically. The electric field is applied via deposited electrodes on the X faces of the bar. This accesses the r22 electro-optic coefficient which has the value of approximately 6.7 x 10-12mV-1 for static electric fields and a little over half this for rapidly varying fields. Why the difference? This is because the static value includes a contribution from the piezo-optic effect where the application of an electric field mechanically strains the crystal and induces an additional optical phase change. For changes of electric field which occur sufficiently quickly, the molecular displacement required to induce the additional strain component cannot follow the electric field and the material operates in the so called "constant Strain" or "clamped" mode and sensitivities are much lower. It is therefore important to be sure of whether stated half wave voltages are defined at dc or under ac drive. Although this orientation provides a simple mode of operation, the r22 electro-optic coefficient is not especially high and the difference between the ac and dc values may be significant for some applications (especially where modulation at low to moderate frequencies is required). In this case, an alternative orientation using optical propagation down the X axis with the electric field applied across the Z axis is available. This utilizes the r13 electro-optic coefficient which has the value of approximately 8.6 x 10-12mV-1. As this orientation is not piezo electrically active, there is no significant difference between the clamped and unclamped electro-optic coefficient and ac and dc fields produce the same modulation. This mode of operation however is not well suited to Q-switching because two crystals must be employed, orientated for static birefringence cancellation. The additional surfaces cause extra loss and increases potential problems with multiple reflections etc. This type of device is not therefore as popular as the more usual Z-cut modulator. Some examples of the typical static field half wave voltages (Vp) of a transverse lithium niobate cell using the z-cut geometry and suggested sizes are given in the following table. Remember to approximately double these for fast switching applications (such as Q-switching).
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Transverse Field Pockels Cells -  - Electro Optical Components, Inc.
Santa Rosa, CA, USA
Transverse Field Pockels Cells
Transverse Field Pockels Cells
Unlike the EM500 range of Pockels cells, the transverse field Pockels cells can be made in a more flexible range of sizes and in a greater choice of materials. The construction usually consists of either one Z-cut crystal in the case of lithium niobate, or two X or Y cut crystals, orientated for birefringence cancellation in the case of lithium tantalite. Other materials are available to suit special requirements, but none can match these for their established quality and low cost. For most applications, the designs can be mounted in a simple machined aluminum alloy channel housing of an appropriate size to match the crystal(s). If necessary, this may incorporate special fixing or other dimensional requirements at a moderate cost. Lithium Niobate (LiNbO3) Lithium Niobate (LiNbO3) is a very important material for transverse Pockels cell manufacture. It possesses excellent transparency over a wide spectral range of 450nm to just over 4μm. Optical damage can be a problem at short wavelengths because of color center formation. Above 800nm, however, this effectively disappears and the material then has a very good optical damage resistance. This makes it very suitable for Q-switching compact Nd+ lasers such as found in laser rangefinders. There are two orientations which may be used successfully for lithium niobate electro-optic devices and the choice is usually determined by the application. The first and the simplest involves using a z-cut bar where the optical axis of the material is parallel to the direction of optical propagation so there is no birefringence encountered. This simplifies the design of the optical system as good thermal stability is ensured automatically. The electric field is applied via deposited electrodes on the X faces of the bar. This accesses the r22 electro-optic coefficient which has the value of approximately 6.7 x 10-12mV-1 for static electric fields and a little over half this for rapidly varying fields. Why the difference? This is because the static value includes a contribution from the piezo-optic effect where the application of an electric field mechanically strains the crystal and induces an additional optical phase change. For changes of electric field which occur sufficiently quickly, the molecular displacement required to induce the additional strain component cannot follow the electric field and the material operates in the so called "constant Strain" or "clamped" mode and sensitivities are much lower. It is therefore important to be sure of whether stated half wave voltages are defined at dc or under ac drive. Although this orientation provides a simple mode of operation, the r22 electro-optic coefficient is not especially high and the difference between the ac and dc values may be significant for some applications (especially where modulation at low to moderate frequencies is required). In this case, an alternative orientation using optical propagation down the X axis with the electric field applied across the Z axis is available. This utilizes the r13 electro-optic coefficient which has the value of approximately 8.6 x 10-12mV-1. As this orientation is not piezo electrically active, there is no significant difference between the clamped and unclamped electro-optic coefficient and ac and dc fields produce the same modulation. This mode of operation however is not well suited to Q-switching because two crystals must be employed, orientated for static birefringence cancellation. The additional surfaces cause extra loss and increases potential problems with multiple reflections etc. This type of device is not therefore as popular as the more usual Z-cut modulator. Some examples of the typical static field half wave voltages (Vp) of a transverse lithium niobate cell using the z-cut geometry and suggested sizes are given in the following table. Remember to approximately double these for fast switching applications (such as Q-switching).

Unlike the EM500 range of Pockels cells, the transverse field Pockels cells can be made in a more flexible range of sizes and in a greater choice of materials. The construction usually consists of either one Z-cut crystal in the case of lithium niobate, or two X or Y cut crystals, orientated for birefringence cancellation in the case of lithium tantalite. Other materials are available to suit special requirements, but none can match these for their established quality and low cost.

For most applications, the designs can be mounted in a simple machined aluminum alloy channel housing of an appropriate size to match the crystal(s). If necessary, this may incorporate special fixing or other dimensional requirements at a moderate cost.

Lithium Niobate (LiNbO3)

Lithium Niobate (LiNbO3) is a very important material for transverse Pockels cell manufacture. It possesses excellent transparency over a wide spectral range of 450nm to just over 4μm. Optical damage can be a problem at short wavelengths because of color center formation. Above 800nm, however, this effectively disappears and the material then has a very good optical damage resistance. This makes it very suitable for Q-switching compact Nd+ lasers such as found in laser rangefinders.

There are two orientations which may be used successfully for lithium niobate electro-optic devices and the choice is usually determined by the application. The first and the simplest involves using a z-cut bar where the optical axis of the material is parallel to the direction of optical propagation so there is no birefringence encountered. This simplifies the design of the optical system as good thermal stability is ensured automatically. The electric field is applied via deposited electrodes on the X faces of the bar. This accesses the r22 electro-optic coefficient which has the value of approximately 6.7 x 10-12mV-1 for static electric fields and a little over half this for rapidly varying fields.

Why the difference? This is because the static value includes a contribution from the piezo-optic effect where the application of an electric field mechanically strains the crystal and induces an additional optical phase change. For changes of electric field which occur sufficiently quickly, the molecular displacement required to induce the additional strain component cannot follow the electric field and the material operates in the so called "constant Strain" or "clamped" mode and sensitivities are much lower. It is therefore important to be sure of whether stated half wave voltages are defined at dc or under ac drive.

Although this orientation provides a simple mode of operation, the r22 electro-optic coefficient is not especially high and the difference between the ac and dc values may be significant for some applications (especially where modulation at low to moderate frequencies is required). In this case, an alternative orientation using optical propagation down the X axis with the electric field applied across the Z axis is available. This utilizes the r13 electro-optic coefficient which has the value of approximately 8.6 x 10-12mV-1. As this orientation is not piezo electrically active, there is no significant difference between the clamped and unclamped electro-optic coefficient and ac and dc fields produce the same modulation. This mode of operation however is not well suited to Q-switching because two crystals must be employed, orientated for static birefringence cancellation. The additional surfaces cause extra loss and increases potential problems with multiple reflections etc. This type of device is not therefore as popular as the more usual Z-cut modulator.

Some examples of the typical static field half wave voltages (Vp) of a transverse lithium niobate cell using the z-cut geometry and suggested sizes are given in the following table. Remember to approximately double these for fast switching applications (such as Q-switching).

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Technical Specifications

  Electro Optical Components, Inc.
Product Category Q-switches
Product Name Transverse Field Pockels Cells
Q-switch Type Electro-optic
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