DC FIELD-INDUCED RESONANCE AND POLARIZATION EFFECTS IN 2-PHOTON TRANSITIONS BETWEEN ATOMIC STATES WITH DIFFERENT PARITY

A resonance, induced by a DC field in a two-photon transition of an at om between states with opposite parity, results in a number of new eff ects related to the polarization of photons. These effects are caused by the interference of the non-resonant second-order dipole-forbidden amplitude and of a resonant part of the DC field-induced third-order a mplitude. The linear and circular dichroism for the cross section of t he process is revealed and analysed in detail for a two-photon excitat ion of the n(f)P state from the ground n(i)S state with a resonance on an n'S state, induced by a DC electric field. The numerical data for alkali atoms demonstrate that the effects have quantitative characteri stics of sufficiently large magnitudes and may be observed in experime nts.