Abstract: A process for measuring electric voltages and/or electric fields by the use of a crystal with an electro-optical (Pockels) effect. To this end, in a direction transverse to the direction of propagation (y direction) of a light wave polarized in the z direction, an electric field intensity gradient is generated in the crystal in the direction from which results a corresponding gradient in the refractive index n of the crystal. This produces a deflection of the light wave in the crystal which depends upon the field intensity and on emergence, it is used as a measure for the voltage of field intensity. A suitable sensor for this purpose is also described.