Investigating transfer of coherence, direction of light propagation and Rydberg blockade in a four-level [formula omitted]-type system under linear and nonlinear interaction regimes.

This theoretical study reveals that the transfer of coherence (TOC) and the direction of light propagation vector play a crucial role in transitioning from electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA) in a four-level closed and open cascade (Ξ)-type light-atom interacting systems (LAIS) under both linear as well as nonlinear interaction regimes. It is found that the amplitudes of the coherence signals are distinctly influenced by the system's openness driven by the presence of additional dipole allowed levels not connected by the lasers and the type of interaction regimes. The effect of TOC on the EIT to EIA transition is discussed in detail by the velocity-dependent dressed state analysis and velocity mapping of the probe absorption coefficient. The findings also reveal that the efficiency of the counter-propagation scheme of the coupling fields is higher than the co-propagation scheme. Furthermore, we have estimated the Rydberg blockade effect on the probe absorption profiles for some specific velocity groups of atoms, which exhibit probe gain in the medium along with EIT and EIA patterns. [ABSTRACT FROM AUTHOR]