Dielectric field gradient tensor

According to equation (6.180), a dielectric force acts on a dipole momentp situated in an inhomogeneous electric field E, that is, a field with a nonzero gradient tensor A.E ... 

Interestingly, the contributions from the gradient of the electromagnetic field across the interface, Tfg xx and Tfg zzz, which scale with the mismatch in the optical dielectric constants of the media forming the interface [37], only appear in the susceptibility tensor components nd xl zzz- Therefore, these contributions may be rejected with a... 

---