Observation of EIA in closed and open caesium atomic system

We present an experimental study on electromagnetically induced absorption (EIA) in the closed transition of a degenerate two-level Cs atomic system.The coupling and probe lasers coupled with the transition 6S_1/2 F=4 \to 6P_3/2F'=5 of caesium atom. The signal of EIA was obtained and the frequency detuning and intensity effect of the pumping laser were experimentally investigated. The EIA signal in 6S_1/2 F =4 \to 6P_3/2F'=4 and 6S_1/2 F =4 \to 6P_3/2F'=3 open transitions was also obtained. As the repumping laser couples with the transition of 6S_1/2 F =3 \to 6P_3/2F'=4, the EIA signal is increased due to the hyperfine optical pumping.