Pulse propagation in an atomic medium under spontaneously generated coherence, incoherent pumping, and relative laser phase

Influences of spontaneously generated coherence (SGC) and relative phase of laser fields on a probe laser pulse propagating in a three-level cascade atomic medium under incoherent pumping and electromagnetically induced transparency (EIT) are studied theoretically. It is shown that the leading edge of the pulse oscillates during its propagation. Furthermore, the oscillating magnitude is enhanced by growing SGC, however, it can be depressed by choosing a suitable relative phase between the laser fields. Indeed, the probe pulse depends sensitively on the relative phase with a period of 2 π in which it oscillates strongest at ϕ=0, π and 2 π; whereas it is unchanged at ϕ=π∕2 and 3π/2. On the other hand, the influences of SGC and the relative phase on the pulse envelope are more effective as growing the incoherent pumping rate.