ABSTRACT
In theoretical studies of (single) photon emission from an atom it is of central importance to describe the time development of the field-atom interaction. When the interaction has been brought to an end a transverse photon has been released from the atom. Traditionally, farfield detection of the T-photon is used to obtain information on the field-atom interaction process. In far-field detection schemes it is in the overwhelming majority of cases sufficient to assume that the released photon field spreads out from a single point in space. This point we call “the position of the atom.” Although it certainly is necessary to take into account the spatial variation of the electromagnetic field across the atomic domain in studies of electric quadrupole, magnetic dipole, and higher-order multipole interaction processes, it is nevertheless an extremely good approximation to consider the atom as a point-like entity in optical far-field studies. In the literature one often encounters the point of view that the emitted T-photon comes from (is generated in) a volume coincident with the electronic size of the atom. Since atomic radii are of the order 1-10 A˚ the above view makes it intuitively easy to consider the atom effectively as a point entity in far-field optics.
