Sub-Doppler absorption narrowing in V, Λ and N-type atom at intense laser fields

Electromagnetically induced transparency and absorption is observed in a transmission of the coupling laser, locked to transition between hyperfine levels of the ground and excited states of Rb-85. The transmission was monitored in a V, A and N - type systems while the probe laser, with similar power as the coupling laser, scans across the hyperfine levels F' of the P-2(3/2) state. The measured width of the EIT resonance increases with a square-root dependence of laser intensity. The EIA was observed only for a cycling transition and for F' = F+1, where F and F are the angular momentum of the hyper-fine levels of the S-2(1/2) and P-2(3/2), respectivly. We demonstrated the effect of a three-photon EIA in a four-level scheme that involves the Raman transitions via virtual level.