Coherent control of AC Stark allowed transition in I⟩ system

A three level I > system is considered and the coherence established on initially forbidden transition is calculated. It is shown that quantum-interference-related phenomena, such as electromagnetically induced transparency, gain without inversion and enhanced refractive index may occur on such transitions, which became dynamically allowed due to AC Stark effect. Gain/dispersion characteristics of such transitions strongly depend upon the relative phase between the driving and probe fields. Unlike allowed transitions, gain/absorption behavior of forbidden transitions exhibit antisymmetric feature on the Rabi sidebands. Absorption/gain spectra possess extremely narrow sub-natural resonances.