Contribution of evanescent waves to the far field: the atomic point of view

Evanescent modes of the electromagnetic field are seldom invoked in convent ional far-field optics, as their contribution far from the source (a few wa velengths) is negligible. Contradicting this fact, in recent theoretical wo rks, based on a particular decomposition of the free-space Green tensor, it has been asserted that evanescent waves do indeed contribute to the far fi eld, where they appear as an additional similar to 1/r component of the fie ld. We provide an explicit demonstration that evanescent modes do not contr ibute to the power radiated to the far field by any dipolar source. First w e derive an expression for the free-space field susceptibility in which con tributions from evanescent and homogeneous modes are separated, and then we use linear response theory to compute the decay rate for an atomic dipole in vacuum. (C) 2000 Optical Society of America OCIS codes: 260.2510, 350.56 10.