Resonant enhancement of an oscillating electric field in an atom

摘要： When an atom is placed into an oscillating electric ?eld with frequency far from atomic resonances, the atomic electrons partly shield this ?eld at the nucleus. It is conjectured that when the frequency of an electric ?eld reaches an atomic resonance, the electric ?eld at the nucleus may be signi?cantly enhanced. In this paper we systematically study the mechanisms of this enhancement and show that it may reach ?ve orders in magnitude in particular cases. As an application, we consider laser-assisted neutron capture in 139-lanthanum nucleus and screening and resonance enhancement of nuclear electromagnetic transitions by electrons.