Abstract

The surface van der Waals (vW) attraction exerted on a neighboring atom, which is related to the nonretarded limit of fundamental QED cavity process, can also be described as the well-known coupling between an instantaneous atomic dipole and its induced electric image. Such a dipole-dipole interaction, governed by a $\left(D^2+D_{\text{z}}^2\right)/16{\text{z}}^3$ Hamiltonian (D: dipole operator, z: distance to the wall) exhibits a cylindrical symmetry around the surface normal and combines a scalar and a quadrupolar contribution. Until now, no attempt had ever been made to observe a signature of the anisotropy induced by the quadrupolar contribution, while recent selective reflection spectroscopy (SR) experiments^1,2 yield rather precise measurements of the strength of the vW interaction.

© 1994 IEEE