Resonances of electromagnetically induced transparency and absorption in a light field of elliptically polarised waves

Electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) resonances excited by a strong two-frequency field are considered for various values of the total angular momenta of the ground (F_g) and excited (F_e) states at a degenerated optical closed transition F_g → F_e. The light field is formed by two co-propagating waves with arbitrary elliptical polarisations. The process of spontaneous transfer of anisotropy from the excited state to the ground state is shown to determine the formation of the EIA resonance at the transition F_g = F → F_e = F + 1. The results obtained generalise the classification of transitions into 'bright' (F_g = F → F_e = F + 1) and 'dark' (F_g = F → F_e = F and F_g = F → F_e = F – 1) transitions with respect to the direction of a subnatural resonance.