Electro-optic sensors for electric field measurements II Choice of the crystals and complete optimization of their orientation

We present a simple method to determine both direction of the electric field component to which an electro-optic sensor is sensitive and sensitivity to this component. For this purpose we introduce the concept of an electro-optic sensitivity vector. This work is done for electro-optic sensors working as amplitude modulators, as phase modulators, or as polarization state modulators. The method applies to any anisotropic crystal, regardless of crystallographic group. After defining three kinds of electro-optic sensor geometry that allow longitudinal, transversal or fully vectorial electric field probing, we make a comparative study of several commonly used electro-optic crystals. We derive the optimal orientations of the crystals with respect to the optical probe beam that lead to high-performance electro-optic sensors. We also treat isotropic crystals in the case of polarization state modulators. In contrast to anisotropic crystals that are sensitive to a unique electric field component, we show that isotropic crystals are sensitive to two orthogonal electric field components simultaneously.