摘要： The electrooptic effect is the change in refractive index of a material induced by the presence of a static (or low-frequency) electric field. In some materials, the change in refractive index depends linearly on the strength of the applied electric field. This change is known as the linear electrooptic effect or Pockels effect. The linear electrooptic effect can be described in terms of a nonlinear polarization given by Pi(ω) = 2ε0 Σj k χ(2)ij k (ω = ω + 0)Ej (ω)Ek(0). Since the linear electrooptic effect can be described by a second-order nonlinear susceptibility, it follows from the general discussion of Section 1.5 that a linear electrooptic effect can occur only for materials that are noncentrosymmetric. Although the linear electrooptic effect can be described in terms of a second-order nonlinear susceptibility, a very different mathematical formalism has historically been used to describe the electrooptic effect; this formalism is described in Section 11.2 of this chapter. In centrosymmetric materials (such as liquids and glasses), the lowest-order change in the refractive index depends quadratically on the strength of the applied static (or low-frequency) field. This effect is known as the Kerr electrooptic effect or as the quadratic electrooptic effect. It can be described in terms of a nonlinear polarization given by Pi(ω) = 3ε0 Σj kl χ(3)ij kl(ω = ω + 0 + 0)Ej (ω)Ek(0)El(0).