  We studied the excitation dynamics of a finite quantum system with an intense
optical near field (ONF) from a perspective of light-dressed states. A simple
model consisting of a single electron and a nano-sized short dipole source were
employed. By calculating the time-dependent wave function subjected to the ONF,
we demonstrated that the optical responses involved not only the first- and
third-order but also the second-, fourth-order harmonic generations that were
not obtained from conventional spatially homogeneous laser fields. In order to
elucidate the origins of the exotic high-order harmonic generations, the
dressed states altered by the ONF were explored. The result showed that the
spatial distribution of the dressed states were significantly influenced by the
ONF, making forbidden optical transitions to be allowed by parity breaking.
This was caused by the spatial inhomogeneousness of the ONF, specifically its
asymmetry, that was inherited to the dressed states.
