Dipole field tensor Subject

Among these response properties the most known are the dipole polarizability tensors a, P, and y, that give flic first three components of flie expansion of a dipole moment t subjected to an external homogeneous field F ... 

The polarization P is given in tenns of E by the constitutive relation of the material. For the present discussion, we assume that the polarization P r) depends only on the field E evaluated at the same position r. This is the so-called dipole approximation. In later discussions, however, we will consider, in some specific cases, the contribution of a polarization that has a non-local spatial dependence on the optical field. Once we have augmented the system of equation B 1.5.16. equation B 1.5.17. equation B 1.5.18. equation B 1.5.19 and equation B 1.5.20 with the constitutive relation for the dependence of Pon E, we may solve for the radiation fields. This relation is generally characterized tlirough the use of linear and nonlinear susceptibility tensors, the subject to which we now turn. 

The A, B,... terms are also present in the expansion series of the dipole when the molecule is subjected to higher derivatives of F. For example, the tensor A determines both the quadrupole induced by a uniform field and the dipole induced by a field gradient. 

---